В данном разделе вы найдете перечень узкоспециализированных названий и определений с их толкованием и расшифровкой. В словаре содержатся не только слова и словосочетания, но и различные аббревиатуры. Так же в конце перечня приведен вариант всех терминов на английском языке. Надеемся, что данный список слов вам поможет быстрее разобраться в этой непростой тематике.
PacketAssist ™ - предложенная компанией VCON концепция обеспечения качества и управляемости при передаче мультимедийной информации в IP сетях. Основные направления:
100Base-T - наиболее часто используемая реализация стандарта Fast Ethernet с использованием неэкранированного кабеля на основе двух скрученных пар (Тwisted pair - "витая пара", отсюда буква Т в обозначении). Число " 100 " означает пропускную способность 100 Мбит/сек.
10Base-2 - реализация стандарта Ethernet с использованием тонкого коаксиального кабеля. Называется также Thinnet и Cheapernet. Максимальная длина сегмента составляет 185 метров (отсюда цифра 2 в обозначении - длина сегмента округлена до 200 метров ). Число " 10 " означает пропускную способность 10 Мбит/сек.
10Base-5 - реализация стандарта Ethernet с использованием толстого коаксиального кабеля. Называется также Thicknet. Максимальная длина сегмента составляет 500 метров (отсюда цифра 5 в обозначении). Число " 10 " означает пропускную способность 10 Мбит/сек.
10Base-T - наиболее часто используемая реализация стандарта Ethernet с использованием неэкранированного кабеля на основе двух скрученных пар (Тwisted pair - "витая пара", отсюда буква Т в обозначении). Число " 10 " означает пропускную способность 10 Мбит/сек.
352 x 288 - разрешение CIF , наиболее часто используемое для передачи видео.
Aliasing - Алиасинг . Эффект, воспринимающийся как высокочастотный шум из-за недостаточной частоты дискретизации при аналогово-цифровом преобразовании. Уменьшить этот эффект можно с помощью фильтрации сигнала.
Analog signal - Аналоговый сигнал - сигнал, представленный непрерывным (в отличие от дискретного) изменением той или иной физической величины (например, человеческая речь). Информация передается изменением частоты , амплитуды или фазы.
Application sharing - Совместное использование приложений - механизм конференцсвязи, позволяющий участникам сеанса связи одновременно каждому на своем экране использовать одну и ту же копию программы, работающую с одним документом и видеть процесс работы других участников.
Aspect ratio - отношение ширины изображения к высоте.
Audiographics - Аудиографика - совместное использование телефонии и графики, например совместная удаленная работа над документами.
Automatic Bandwidth Adjustment - Автоматическая настройка полосы - Алгоритм, используемый оконечными устройствами в H.323 для автоматического увеличения или уменьшения скорости передачи битового потока в зависимости от состояния сети.
B channel - B-канал - канал, используемый в системах ISDN для передачи пользовательской информации - голосовых сигналов или потока данных. Полоса B канала составляет 64 Кбит/сек., два B-канала могут быть объединены в один с полосой 128 Кбит/сек. Типичная городская телефонная линия может обеспечить два B-канала. См. также D-канал .
Bandwidth - Полоса частот, пропускная способность . Количественное выражение способности канала передавать информацию. Для аналоговых каналов - разность между наибольшей и наменьшей частотой возможного сигнала. Для цифровых каналов - максимальное количество бит в секунду.
Bit rate - Скорость передачи (обмена) информации в канале. Измеряется в bps .
Bps - Бит в секунду , единица измерения скорости передачи данных и пропускной способности цифровых каналов.
BRI (Basic Rate Interface) - наиболее распространенная форма ISDN-соединения для связи по обычным телефонным проводам. BRI обеспечивает связь по двум информационным B-каналам 64 Кбит/с. каждый и одному служебному D-каналу 16 Кбит/с.
Broadcasting - Широковещательная передача - Технология распространения информации в сети с коммутацией пакетов, когда один поток данных получают сразу все пользователи сети.
CCITT (Consultative Committee for International Telephony & Telegraphy) - Международный консультативный комитет по телефонии и телеграфии (МККТТ) . С 1993 года называется Международный Союз Электросвязи - Сектор стандартизации для телекоммуникаций ( ITU-T ). Разрабатывает технические стандарты, известные как "Recommendations" (рекомендации) по всем международным аспектам цифровых и аналоговых коммуникаций.
Chaircontrol (управление председателем) - в сеансе многоточечной связи выбирается Председатель, который управляет сеансом, последовательностью показа участников и т.д. (см. Управляемая конференция).
Chaircontrolconference (управляемая конференция) - организация многоточечной конференции, когда один из участников сеанса связи получает функции Председателя и может управлять сеансом по своему усмотрению. Управляемую конференцию еще называют конференцией с управлением Председателем.
CIF (Common Itermediate Format) - Общий Формат Обмена - используемый в телеконференциях стандарт видеоизображения с размером кадра 352х288 пикселов и частотой кадров 7.5, 10, 15 или 30 к/сек. Цвет кодируется в формате YUV с разрядностью 8 бит. Производные форматы: QCIF - 176х144 пикселов, subQCIF - 128x96 пикселов, 4CIF - 704x576 пикселов, 16CIF - 1408x1152 пикселов.
Circuitswitching (коммутация каналов) - коммуникационная модель, в которой между двумя точками организуется выделенный канал, используемый для передачи пакетов. Канал существует только во время передачи, а по окончании ее закрывается. После закрытия соединения его могут использовать другие хосты. Примером сетей с коммутацией каналов являются телефонные сети общего пользования .
Codec (кодек) - аппаратное и программное обеспечение, осуществляющее преобразование аналогового сигнала в цифровую форму с последующим преобразованием цифрового сигнала, так что он может быть передан по более узкополосным каналам связи (кодирование). На приемном конце аналогичный кодек осуществляет восстановление первоначального цифового сигнала и преобразование его в аналоговую форму (декодирование). Применение таких устройств в аппаратуре для видеоконференций позволяет использовать узкополосные линии связи.
Coder (кодер) - аппаратное и программное обеспечение для кодирования аналогового сигнала в цифровой , составная часть кодека .
Compositevideo (композитный (смешанный) видеосигнал) . Чаще всего используется для передачи видеоизображений. Составляющие яркости, цветности и насыщенности на передающей стороне мультиплексируются вместе в один сигнальный провод и разделяются на принимающей стороне. Технология композитного видео используется в бытовых камерах, видеомагнитофонах и телевизорах. Для соединения видеоустройств обычно применяются одноштырьковые соединители "тюльпан".
Compression (сжатие) - метод, позволяющий уменьшить число битов, представляющих данную информацию для передачи или хранения. Компрессия снижает требуемую для передачи полосу или экономит память, используемую для хранения.
Continuous presence - возможность в многоточечной конференции воспроизводить на экране видеоизображение сразу нескольких участников.
CRT - Cathode-Ray Tube (ЭЛТ - электронно-лучевая трубка ) - тип трубки, используемый в телевизионных и компьютерных дисплеях или дисплей, ее использующий.
D channel (D-канал) - канал, используемый в системах ISDN для передачи сигналов управления и другой служебной информации. Полоса D канала составляет 16 Кбит/сек. (для BRI ) или 64 Кбит/сек. (для PRI ). См. также В-канал .
DCT - Discrete Cosine Transform (дискретное косинусное преобразование (ДКП) - двумерное дискретное косинусное преобразование, разработанное в 1981 году старшим научным сотрудником лаборатории сжатия Сан-Хосе В.Ченом. Является основой большинства методов сжатия неподвижных и подвижных изображений, сопровождающихся потерей части информации, таких, как в стандатах JPEG , MPEG , H.261 , H263 .
Decoder (декодер) - аппаратное и программное обеспечение для декодирования цифрового сигнала в аналоговый, составная часть кодека .
Digital signal (цифровой сигнал) - представление физического сигнала в виде ряда чисел, представляющих амплитуду или интенсивность. Используемый диапазон чисел - главный определяющий фактор отношения сигнал-шум.
Document sharing (совместное использование документов) - возможность конференции, позволяющая участникам одновременно работать над одним и тем же документом.
Document stand (документальная камера) - устройство со встроенной видеокамерой для захвата изображений бумажных документов.
Drawing board (планшет) - устройство ввода в компьютер графической информации или координат, обычно используемое в автоматизированном проектировании.
E1 - используемый в Европе тип сервиса для цифровой передачи данных с пропускной способностью 2.048 Мбит/с, подобный используемому в Северной Америке Т1
Echo cancellation (эхоподавление) - технология, используемая в громкоговорящих системах аудио- и видеоконференцсвязи для устранения эха, вызванного обратной связью через микрофон. Она основана на "запоминании", какой сигнал попадает на колонки и вычитании его (с соответствующим ослаблением и задержкой) из сигнала идущего с микрофона. Сложность состоит в определении правильной величины задержки и коэффициента ослабления. Эхоподавление требует значительного объема вычислений.
Ethernet - стандарт де-факто для локальных сетей , предложенный компанией Xerox и расширенный совместно Xerox, Intel и DEC. Ethernet использует полосу 10 Мбит/сек и метод множественного доступа с обнаружением конфликтов.
Fast Ethernet - стандарт для локальных сетей, использующий полосу 100 Мбит/сек. Является развитием стандарта Ethernet. Распространенной реализацией этого стандарта является 100Base-T .
Filtration (фильтрация) - способ удаления нежелательных частот из сигнала. Обычно фильтрация используется для удаления высокочастотных составляющих аудио и видеосигналов, чтобы избежать алиасинга при оцифровке . Фильтрация не уменьшает количество данных, т.к. количество сэмплов и число бит остаются такими же, как и без фильтрации. При правильной фильтрации выходной сигнал звучит или выглядит лучше.
Frequency (частота) - количество периодов в единицу времени (например, частота звука или радиоволны).
Full duplex (полный дуплекс) - режим одновременной передачи и приема в обоих направлениях, в отличие от попеременной передачи и приема ( полудуплекс ).
G.711 - рекомендация ITU-T , способ кодирования звука, обеспечивающий полосу аудиосигнала примерно 3.5 КГц в канале 64,000-бит/сек.
G.722 - рекомендация ITU-T , способ кодирования звука, обеспечивающий полосу аудиосигнала примерно 7 КГц в канале 48,000-, 56,000-, или 64,000-бит/сек.
G.723 - рекомендация ITU-T , способ кодирования звука, обеспечивает полосу аудиосигнала примерно 3.5KHz в канале связи 6,300-бит/сек.
G.728 - рекомендация ITU-T , способ кодирования звука, обеспечивает полосу аудиосигнала примерно 3.5-KHz в канале связи 16,000-бит/сек.
GateKeeper (привратник) - сервисная программа, контролирующая доступ к видеоконференции , основанной на стандарте H.323 в сетях с пакетной коммутацией . Она требует, чтобы терминалы зарегистрировались на Привратнике, сообщив ему свое имя. Привратник осуществляет трансляцию сетевых адресов и алиасов для установления соединения. Он может отказать в доступе или ограничить число одновременных соединений в зависимости от загруженности сети. Множество терминалов, шлюзов и MCU , управляемых одним Привратником составляют зону .
Gateway (шлюз) - позволяет системам, существующим в разных сетях и основанным на разных H.32x стандартах, связываться между собой. Среди них: H.320 (ISDN), H.321 (ATM), H.322 (iso Ethernet), H.323 ( IP ), H.324 ( POTS ).
Gray scale (шкала оттенков серого) - представление изображения, когда цветноть и насыщенность убирается до нуля. Фактически это только яркостная составляющая изображения.
H.221 - рекомендация ITU-T "Структура кадра при предаче аудиовизуальной информации для каналов 64-1920 Kbit/s"; определяет использование B-каналов для передачи мультиплексированных аудио-, видеоданных и другой информации.
H.261 - рекомендация ITU-T "Видео кодек для передачи аудиовидеоданных в канале P x 64 Kbit/s". P может меняться в диапазоне от 1 до 30. Кодирование основано на ДКП , предсказании перемещения и использовании кода с переменной длиной. Рекомендация регламентирует алгоритмы кодирования для передачи видео в форматах CIF и QCIF с частотой до 30 кадр./с.
H.263 - рекомендация ITU-T "Кодирование видео для низкоскоростных соединений" - метод кодирования, разработанный для H.324 , использующий технологию H.261 с дополнительными усовершенствованиями.
H.320 - рекомендация ITU-T "Узкополосные видеотелефонные системы и терминальное оборудование" - определяет стандарты для видеоконференцсвязи в сетях ISDN и им подобных.
H.323 - рекомендация ITU-T "Видеотелефонные системы и терминальное оборудование для локальных сетей с негарантированным качеством услуг" (версия 2 - "Мультимедийные системы связи для сетей с коммутацией пакетов") - определяет стандарты для видеоконференцсвязи в локальных , корпоративных и глобальных сетях с коммутацией пакетов .
H.324 - рекомендация ITU-T "Терминал для низкоскоростной мультимедийной связи" - определяет стандарты для видеоконференцсвязи с использованием обычных телефонных линий ( POTS) .
Half duplex (полудуплекс) - двухсторонняя поочередная передача со сменой направления (в отличие от полного дуплекса ).
Hue (оттенок) - атрибут визуального восприятия цвета, в соответствии с которым цвет области выглядит похожим на один или смесь двух из следующих цветов: красного, желтого, зеленого и синего.
IMUX - Inverse Multiplexer (демультиплексор) - устройство для разделения одного широкополосного канала на несколько узкополосных. См. мультиплексирование .
INTER - Interframe coding (межкадровое кодирование) - кодирование последовательности кадров, основанное на передаче только изменений текущего кадра по сравнению с предшествующим.
INTRA - Intraframe coding (внутрикадровое кодирование) - кодирование отдельного кадра, использующее только избыточность в изображении самого кадра.
IP - Internet Protocol (протокол сетевого уровня), используемый в Интернет и других компьютерных сетях. Обеспечивает передачу пакетов без организации соединений и гарантии доставки.
IPX/SPX - "Internet Packet eXchange/Sequenced Packet eX-change," - семейство протоколов, первоначально используемых в сетях NetWare. (Некоторые сети NetWare используют TCP/IP вместо IPX/SPX, многие сети NetWare используют оба семейства протоколов.)
ISDN - Integrated Services Digital Network (цифровая сеть с интеграцией услуг) ISDN - стандартизованный способ предоставления цифровых услуг по цифровым телефонным линиям. Основные интерфейсы - BRI и PRI .
ITU-T - International Telecommunications Union-Telecommunications standardization sector (Международный Союз Электросвязи) - сектор стандартизации для телекоммуникаций; выпускает "рекомендации" для стандартных протоколов. Раньше назывался CCITT .
JPEG (Joint Photographic Experts Group) - международная группа по разработке стандартов кодирования неподвижных изображений; стандарт кодирования неподвижных изображений.
LAN - Local Area Network (ЛВС - Локальная Вычислительная Сеть) - сеть передачи данных, связывающая компьютеры и другие устройства, расположенные на незначительном удалении один от другого (комната, здание, предприятие) и управляемые специальной операционной системой. Устройства-шлюзы ( Gateway ) применяются для соединения локальных сетей в распределенную сеть и для подключения их к сетям большей протяженности (WAN).
MCU (Multipoint Control Unit) - устройство для реализации многоточечной аудио- и видеоконференции .
Modem - Modulator/Demodulator (модем - Mодулятор/Демодулятор) - устройство, используемое для преобразования последовательности цифровых данных в аналоговый сигнал, подходящий для передачи на значительное расстояние (например, по аналоговым телефонным сетям). В точке приема выполняется обратное преобразование в цифровую форму.
Motion prediction - предсказание перемещения. Техника межкадрового кодирования, применяемая в кодеках для сжатия сигнала движущегося изображения. В проследовательности кадров каждый пиксель на текущем кадре перемещен по сравнению с предшествующим кадром. Но соседние пиксели перемещаются практически одинаково. Кадр делится на блоки пикселей (16х16 или 8х8) и для описания движения пикселей всего блока вычисляется один вектор ( motion estimation - оценка перемещения). Предсказание текущего блока, полученное из предшествующего с кадра помощью вектора перемещения ( motion compensation - компенсация перемещения) сравнивается с настоящим текущим блоком и формируется, если надо, ошибка предсказания (т.е. компенсация неточности предсказания). Для таких блоков передается только вектор перемещения и ошибка предсказания, что значительно экономней простой передачи содержимого блока.
MPEG (Motion Picture Experts Group) - Экспертная группа по разработке стандартов (MPEG) кодирования и хранения видеоизображений; стандарт (MPEG-1, MPEG-2, MPEG-4) кодирования и хранения видеоизображений.
Multicast (групповая рассылка) - организация рассылки в IP сети, позволяющая направить одну копию пакета всем членам группы абонентов. Принадлежность к группе должна инициироваться получателем и поддерживаться сетевым оборудованием.
Multicasting (многоадресная передача) - технология распространения информации в сети с коммутацией пакетов, когда один поток данных получает определенная группа пользователей сети.
Multimedia (мультимедиа) - данные, включающие в себя различные формы естественной информации, обычно звук и видео.
Multiplexing (мультиплексирование) - процесс объединения отдельных потоков или каналов в один логический поток данных таким образом, что они позднее могут быть восстановлены в прежнем виде без ошибок.
Multipoint (многоточечный) - термин для аудио- и видеоконференций с одновременным участием трех и более пользователей.
MUX - Multiplexer (мультиплексор) - устройство для объединения нескольких узкополосных сигналов в один широкополосный. См. мультиплексирование .
Noise-gated microphone - микрофон, который сам выключается в паузах, когда уровень звука стал ниже заданного уровня (а поэтому, скорее всего, является посторонним) и включается снова при увеличении уровня звука, когда кто-то снова начал говорить в микрофон.
NT1 (Сетевой Терминатор 1) - устройство применяемое в ISDN для преобразования двухпроводного соединения в четырехпроводное - подходящее для ISDN телефона. Обычно, терминаторы NT1 позволяют поддерживать несколько четырехпроводных соединений, например, одно для телефона и одно для факса.
NTSC (National Television Standards Committee) - стандарт для цветного телевизионного вещания, разработанный в США, 30 кадров/сек. 525 линий в кадре. Используется в Северной Америке и Японии. Альтернативные системы: PAL , SECAM .
Overlaying video (См. Video overlay ).
PacketAssist ™ - предложенная компанией VCON концепция обеспечения качества и управляемости при передаче мультимедийной информации в IP сетях. Основные направления:
- Управление шириной используемой полосы - устраняет необоснованную загрузку сети;
- Качество обслуживания (QoS) - обеспечивает наилучшее качество аудио и видео при заданной скорости связи.
Packet switching (коммутация пакетов) - коммуникационная модель, в которой пакеты от разных источников и с различной адресацией передаются по одному каналу от маршрутизатора к маршрутизатору. Используется в большинстве компьютерных сетей.
PAL (Phase Alternative Line System) - стандарт для цветного телевизионного вещания, разработанный в Германии, 25 кадров/сек. 625 линий в кадре. Используется в большинстве стран Европы, Африки, Южной Америки и в Австралии. Альтернативные системы: SECAM , NTSC .
PBX (Private branch exchange) - учрежденческо-производственные АТС (УАТС).
Pixel - picture element (пиксель) - наименьшая точка или элемент изображения, обладающий особыми цветовыми и/или яркостными характеристиками.
POTS (Plane Old Telephone System) - обычные аналоговые телефонные сети связи (ТфОП). Допускают наравне с телефонной связью передачу данных со скоростью до 33.6 Кб/с., а также в ограниченных пределах видеоконференцсвязь . Синоним - PSTN .
PRI (Primary rate ISDN) - высокоскоростной канал ISDN. PRI соединение обеспечивает полосу 2.048 Мбит/с. в Европе (30 В-каналов + D-канал), что эквивалентно Е1 , и 1.544 Мбит/с. в Северной Америке (23 В-канала + 1 D-канал), что эквивалентно Т1 .
PSTN (Public Switched Telephone Network) - Коммутируемые сети телефонной связи общего пользования. Представляют собой обычные аналоговые телефонные сети связи. Допускают наравне с телефонной связью передачу данных со скоростью до 33.6 Кб/сек., а также в ограниченных пределах видеоконференцсвязь . Синоним - POTS .
QCIF (Quarter Common Interchange Format) - вариант CIF с разрешением 176 x 144.
QoS - Quality of Service (качество обслуживания) - концепция, обеспечивающая выделение сетевых ресурсов, необходимых для работы приложения.
Resampling - преобразование разрешения с пересчетом значений сэмплов с учетом окружающих.
Resolution (разрешение) - мера детальности цифрового видеоизображения, измеряемая или количеством пикселей в горизонтальном и вертикальном направлениях, или в пикселях на единицу длины (при просмотре на дисплее или печати).
RGB - представление цвета, когда каждый элемент изображения представляется тремя компонентами интенсивности основных цветов - красного, зеленого и синего. Соответствующие смеси этих цветов можно использовать для представления любого цвета.
Router (маршрутизатор) - устройство в сетях с коммутацией пакетов для передачи пакетов из одной подсети в другую.
RSVP - Resource Reservation Protocol (потокол резервирования ресурсов) - протокол, позволяющий приложению запрашивать и резервировать необходимый сетевой ресурс.
RTP/RTCP (Real-Time Transport Protocol/Real-Time Transport Control Protocol) - Транспортный Протокол Реального Времени/ Управляющий Протокол Транспортным Протоколом Реального Времени - Протоколы для передачи в реальном времени аудио- и видеопотоков, их синхронизации, определения и восстановления потерь и передачи другой служебной информации. В качестве транспортного протокола используют UDP .
S-Video - тип электрического сигнала, используемого для передачи видео. Стандарт предусматривает передачу сигналов яркости и цветности в отдельных проводах кабеля с многоштырьковыми разъемами. S-Video обеспечивает более высокое качество изображения по сравнению с композитным видео, т.к. отсутствует ухудшение из-за комбинирования и последующего разделения компонент.
Sample - число, представляющее мгновенную величину сигнала в определенный момент, используется при цифровом представлении сигнала.
Saturation (асыщенность) - аттрибут визуального восприятия цвета, в соответствии с которым область может выглядеть разной при одном оттенке. С изменением насыщенности цвет области можно изменить, например, от небесно голубой до темно синей.
Scaling (масштабирование) - преобразование разрешения без пересчета значений сэмплов, они могут только убираться или добавляться аналогичные (размножаться).
SECAM (Sequentiel couleur a memoire) - стандарт для цветного телевизионного вещания, разработанный во Франции, 25 кадров/сек. 625 линий в кадре. Используется во Франции, странах Восточной Европы и бывшего СССР. Альтернативные системы: PAL , NTSC .
T.120 - серия рекомендаций ITU-T "Передача данных пользователей с помощью многоуровневого протокола" - определяет стандарты для совместного использования данных в видеоконференцсвязи .
T1 - используемый в США тип сервиса для цифровой передачи данных с полосой пропускания 1,544,000 бит/сек. Электрическое соединение использует выделенную линию из двух пар телефонных проводов. Каналы T1 широко используются для подключения PBX к центральному телефонному узлу. Каналы T1 также используют для подключения удаленных сегментов локальных сетей .
TCP - Transmission control protocol (протокол управления передачей) - основной транспортный протокол в в наборе протоколов Internet, обеспечивающий надежные, ориентированные на соединения, полнодуплексные потоки. Для доставки данных используется протокол IP .
Telemedicine (телемедицина)- практическая медицина на расстоянии с использованием компьютерных сетей и/или видеоконференцсвязи .
Temporal filtering (временное фильтрование) - процесс пропускания кадров или фильтрование избыточно мелких деталей между последовательными кадрами как часть кодирования видео.
Touch panel (сенсорная панель) - дисплей, чувствительный к нажатиям для управления оборудованием.
UDP (User Datagram Protocol) - Транспортный протокол в наборе протоколов Internet. Подобно TCP , использует IP для доставки, однако, в отличие от TCP, UDP обеспечивает обмен дейтаграммами без подтверждения гарантии доставки.
Unicasting (одноадресная передача) - технология распространения информации в сети с коммутацией пакетов, когда поток данных идет только к одному получателю.
VGA (Video Graphics Array) - стандарт для графической подсистемы в IBM PC. Впервые появился в компьютере IBM PS/2 в 1987 году. Разрешение у VGA - 640x480. Позднее появился "Супер" VGA (SVGA), с более высокими разрешениями - 800 x 600, 1,024 x 768, 1,280 x 1,024 и др..
Video follows voice (видео следит за голосом) - концепция системы видеоконференцсвязи , которая автоматически наводит камеру на говорящего.
Video overlay (наложение видео) - комбинирование нескольких изображений в виде мозаики. Наиболее общий пример в телевещании - диктор, рассказывающий о прогнозе погоды перед картой. Соответствующий пример в компьютерной видеоконференцсвязи - это показ видеоизображения человека на фоне изображения, сгенерированного компьютером.
Videoconferencing (видеоконференция, видеоконференцсвязь) - обмен оцифрованными видеоизображениями и звуком между двумя или более удаленными сторонами. Передаваемые изображения могут включать потоки видео, неподвижные изображения объектов, информацию или данные из графиков, файлов или приложений. Это позволяет участникам конференции слышать, видеть и сотрудничать в реальном времени со своими собеседниками.
Virtual circuit (виртуальная сеть) - логическое соединение через сеть с коммутацией пакетов, которая временно работает как постоянное физическое соединение.
Visual artefacts (артефакты) - термин для расхождений между декодированным после передачи изображением и оригиналом.
Voice-activated switching (переключение по голосу) - технология организации многоточечных конференций, когда на дисплее обычно показывается видеоизображение абонента с самым громким звуковым сигналом, а этот абонент видит изображение абонента, выбранного перед ним.
YIQ - представление цвета в NTSC. Каждый элемент изображения представляется тремя компонентами: яркостной и двумя цветоразностными.
YUV - представление цвета в PAL и многих других способах кодирования видео. Каждый элемент изображения представляется тремя компонентами: яркостной и двумя цветоразностными.
Zone (зона) - в рекомендации H.323 - множество терминалов, шлюзов и MCU , управляемых одним Привратником . Зона должна включать хотябы один терминал и может включать несколько сегментов ЛВС.
Brightness ratio - The difference between the lightest (whitest) and darkest (blackest) areas in an image. The
CGA - Color Graphics Adapter. Introduced in 1983, it was IBM’s first product to display both color and graphics. CGA has a horizontal scan frequency of 15.75 kHz and a vertical frequency
Delay - A basic DSP process in which the output of the input signal is delayed by a specified time
Differential gain - Unwanted variations in a chrominance subcarrier’s amplitude that result from changes in the
H.320 - ITU-T H.320 is a family of standards developed for video teleconferencing systems using ISDN. It references H.261 (for video); G.711, G.722, and G.728 (for audio); H.221, H.230, H.231, H.233, H.234, H.242, and H.243 (for control).
HTTP - HyperText Transfer Protocol. A Web protocol based on TCP/IP that is used to retrieve
IPX - Internetwork Packet Exchange Protocol. Commonly used over Novell Netware and Microsoft Windows networks.
Networking - Two or more devices (or people) communicating with each other and sharing
Parametric equalizer - A type of audio equalizer having several “parameters” for control of various filters that can
Peak - The highest level of signal strength, as determined by the height of the signal’s
Physical plant - Infrastructure components including cable, connectors, splices, panels, splitters, repeaters and regenerators necessary to propagate the light signal between the
Vertical blanking interval - The blanking time at the beginning of each field. It contains equalizing pulses and vertical
4:2:2 - The ratio of the amount of information among luminance (Y) and two color difference signals (R-Y, B-Y). In digital component video format, it is the ratio of the sampling frequencies of the Y, R-Y, and B-Y. For every four samples of Y, there are two samples each for R-Y and B-Y. In analog component video format, it is the ratio of the bandwidth of the Y, R-Y, and B-Y. Other commonly used ratios are 4:4:4 (all colors are sampled equally; typically describes RGB) and 4:1:1 (the standard for NTSC DV digital video; for every four samples of luminance, each color difference signal is sampled once). See “ITU-R BT.601.”
10/100Base-T - The Ethernet protocol that uses Unshielded Twisted Pair (UTP – Cat 5, etc.) cable, in which the amount of data transmitted between two points in a given amount of time is equal to either 10 Mbps or 100 Mbps.
100Base-TX - IEEE physical layer specification for 100 Mbps over two pairs of UTP or STP wire.
1080i - Interlaced HDTV transmission standard. Refers to an active pixel rate of 1920x1080 with a vertical refresh rate of up to 60 fields (30 frames) per second for NTSC countries or 50 fields (25 frames) per second for PAL/SECAM countries.
1080p - Progressive-scan HDTV standard. Refers to an active pixel rate of 1920x1080 with a vertical refresh rate of up to 60 frames per second for NTSC countries or 50 frames per second for PAL/SECAM countries. 1080p is often stated with an associated frames-per-second rate, such as: 1080p24 (24 fps, progressive), 1080p30 (30 fps, progressive) and 1080p60 (60 fps, progressive). 1080p is extremely rare in broadcasting; for example, the ATSC standard provides bandwidth sufficient only for 1080p24 and 1080p30. Blu-ray and other pre-recorded high definition schemes can support full 1080p60 content playback.
10Base-T - An Ethernet standard that uses twisted wire pairs and transmits data at 10 Mbps.
2:2 film detection - The ability to determine whether PAL video has been converted from film using 2:2 pulldown. Film material with 2:2 pulldown may result in artifacts and jaggies when the video signal is deinterlaced. By using 2:2 film detection to determine if the material originated from film and was converted to PAL, the video processing algorithm can be used to optimize any video for deinterlacing so that the images are free of artifacts.
2:2 pulldown - See “2:2 film detection”
3:2 pulldown - The process of matching the frame rate of film (24 frames per second) to the frame rate of NTSC video (30 frames per second). In 3:2 pulldown, one frame of film is converted to three fields (1 1/2 frames) of video, and the next frame of film is converted to two fields (1 frame) of video. This cadence is repeated (3 fields, 2 fields, 3 fields, 2 fields . . .) until the film is fully converted to a video of approximately the same duration.
3:2 pulldown detection - A sophisticated technology in Extron scalers used to detect the presence of a 3:2 pulldown that helps maximize image detail and sharpness. When film-originated material is detected, this technology applies video processing algorithms that optimize image reproduction and avoids causing jaggies.
3G-SDI - See “SMPTE 424M”
720p - Progressive-scan HDTV transmission standard. Refers to an active pixel rate of 1280x720 with a vertical refresh rate of 60 frames per second for NTSC countries or 50 frames per second for PAL/SECAM countries. The 720p standard also allows refresh rates of 24, 25, and 30 frames per second.
A/D - Analog to Digital (converter). A device that converts an analog signal to a digital value.
A/V - Audio visual, or audio video.
AACS – Advanced Access Content System - A digital rights management standard utilized with Blu-ray Disc and other optical formats. AACS incorporates two parts: a set of embedded decryption keys within the source device, and a set of keys encoded in the content that describes each of the playback devices licensed to utilize the content. This approach allows copyright holders to revoke the keys of a particular source device, thus preventing it from playing back future content. AACS also provides for a managed copy system, that is, a mechanism by which one or several, but not an unlimited number of copies can be legally made as backups, for storage on a media server, or for use on a portable device.
AAP - Architectural Adapter Plate. Mountable metal plates available in hundreds of models offering popular pass-through audio, video, phone, data, power, and control connectors. Active AAPs are also available for power, control, and long distance signal transmission. Along with mounting options for maximum flexibility in placing connectors and controls within reach, these interchangeable components fit together to create an attractive and completely customizable A/V connectivity solution.
Absorption - The attenuation of light as it passes through fiber, similar to the resistive loss of an electrical signal as it passes through cable. Absorption is caused by impurities and defects in the fiber.
AC - Alternating Current. Electron flow that changes direction alternately.
AC coupled - A circuit design that does not pass the DC component of a signal, therefore it ignores DC offsets.
AC-3 - See "Dolby Digital"
Acceptance Angle - In fiber optics, this is the maximum allowable angle of incidence for light entering a fiber measured from the center axis of the fiber. Incoming light must be directed below this angle in order to enter the core of the fiber and propagate along its length through total internal reflection.
Active crossover - A circuit that separates the audio signal into the appropriate frequency bands for the woofer, midrange, and tweeter. An active crossover is placed in the signal path ahead of the amplifier, where a passive crossover is placed between the amplifier and the speaker.
ADC - Apple Display Connector. Common to current Apple displays, non-LCD and LCD alike. One connection routes all power, USB, and digital video signal to the monitor on a single cable.
ADC - Analog to Digital Converter. A device that converts analog signals to digital signals.
Additive color process - Also called “RGB.” A color generation process used in video that combines red, green, and blue to make all colors. All three colors (red, green, and blue) at 100% combine to make white on a video screen; the absence of all three colors (0%) makes black. Also see “Subtractive color process (CMYK).”
ADSP™ - Advanced Digital Sync Processing™. Using sync processing to allow centering control (H-shift or V-shift) can create problems with some display devices because of the sync delay. This means the digital projector user may have to choose between a stable sync and centering control. Extron’s ADSP restores the original sync timing relationship for a stable sync signal while allowing centering control.
ADTV - Advanced Definition Television. An early HDTV system proposed by the Advanced Television Research Consortium in 1992. Now superseded by US HDTV standards.
Aerial Cables - Optical fiber cables designed for outdoor installations on aerial supporting structures such as poles. They are specifically designed to withstand adverse conditions such as wind and ice loading, pollution, UV radiation, thermal cycling, stress, and aging.
AES – Advanced Encryption Standard - A data encryption standard adopted by the US Government and approved by the National Security Agency for top secret information. DCP, LCC, the licensing agency for HDCP, has adopted AES 128 encryption for the new HDCP 2.0 standard.
AES/EBU - Audio Engineering Society/European Broadcasting Union. A digital audio transfer standard. The AES and EBU developed the specifications for the standard. The AES/EBU digital interface is usually implemented using 3-pin XLR connectors, the same type of connector used in a professional microphone. One cable carries both left-and right-channel audio data to the receiving device. Also see “AES3.”
AES3 - A digital audio standard defined by the Audio Engineering Society. The standard specifies several basic physical interconnections between devices: Balanced - 3conductor, 110 ohm cabling with an XLR connector, typically referred to as “AES/EBU audio.”; Unbalanced – 2-conductor, 75 ohm coaxial cable with an RCA connector, typically used in consumer audio applications. In many consumer products such as DVD players and A/V receivers, this is often referred to as a “digital coaxial” connection type; AES-3id - A professional version of the 2-conductor 75 ohm coaxial cable terminated with a BNC connector. AES3 unbalanced and AES-3id audio can be switched or routed using a video switcher with a minimum of 150 MHz (-3 dB, fully loaded) video bandwidth; Optical – Plastic optical fiber using an F05 style connector, typically used in consumer audio applications. In many consumer products, this is often referred to as a “digital optical” connection type. TOSLINK is the most common implementation of this connection type.
AFL™ - Accu-RATE Frame Lock™. Extron’s patented method of eliminating image tearing which is associated with scaling, especially when motion video is involved, and occurs when the input frame rate is slower or faster than the output frame rate and part of the old frame and part of the new frame are displayed at the same time during a refresh cycle.
Extron Accu-RATE - Frame Lock sets and locks the output frame rate to the input frame rate of a designated input and produces a tear-free output in a seamless switching system.
AGC - Automatic Gain Control. A circuit used to automatically control the level of the recorded or transmitted signal. It is sometimes called Automatic Level Control (ALC), or Automatic Volume Control (AVC).
Air Blown Fiber – ABF - Optical fiber installed through special tube cables by means of using pressurized air or nitrogen to “blow” bundles of fibers through individual tubes within the cable. Tube cables are usually preinstalled at the premises before installation of air blown fiber.
Air Polish - In fiber optics, this is the first step in polishing the connector using special fine grit film, after the fiber has been cleaved. ALC Automatic Level Control. In audio recording, a circuit used to control the volume or level of the recorded signal automatically without distortion due to overload. Sometimes called Automatic Gain Control (AGC), or Automatic Volume Control (AVC).
Aliasing - (1) Aliasing occurs when smooth curves and lines become rough or jagged because of a lower resolution device, or by an event. (2) In analog video, aliasing is typically caused by interference between the luma and chroma frequencies or between the chroma and field scanning frequencies. It appears as a moir? or herringbone pattern, straight lines that become wavy, or rainbow colors. Also see “Cross color.” (3) In digital video, insufficient sampling or poor filtering of the signal causes aliasing. Defects typically appear as jagged edges on diagonal lines and twinkling or brightening in picture detail. See “Antialiasing.”
All Dielectric - In fiber optics, this denotes the presence of only dielectric, or non-metal elements.
AM - Amplitude Modulation. A method of radio transmission, by which the information part of the signal causes the amplitude of a carrier frequency to vary without affecting the frequency.
Ambient Sound Level - Any environmental or background sound that exists before a new sound source is added. For example, in a school classroom, ambient sound may come from an adjacent hallway or playground, HVAC system, room lights, or another classroom. Ambient sound must be taken into consideration when designing a sound support system.
American National Standards Institute (ANSI) - ANSI is a private, non-profit organization that administers and coordinates the voluntary standardization and conformity assessment system in the US.
Amp - Ampere. The international base unit of electrical current that represents the rate flow of electric charges through a conductor. Symbolized by “A.” 1 amp is equal to the steady current produced by 1 volt applied across a resistance of 1 ohm.
Amplifier - An electronic device used to increase the voltage amplitude of a signal.
Amplifier classifications - Audio amplifiers are typically described by “class”. There are four primary classes used in A/V system designs: A, B, A/B, and D.
Amplitude - The level or strength of a signal as measured by the height of its waveform. Electronic waveforms can be displayed and measured on an oscilloscope.
Amplitude Modulation – AM - Amplitude modulation is also employed in fiber optics applications, in which light acts as a carrier signal with its amplitude varying in accordance to the signal being conveyed.
Anaerobic - For fiber optics, this describes a method of bonding between optical fibers via a non-heat, intrinsic chemical reaction within the adhesive material. By definition, an anaerobic adhesive does not require air to cure.
Analog - A continuously varying action or movement that takes time to change from one position to another. Standard audio and video signals are analog. An analog signal has an infinite number of levels between its highest and lowest value (unlike digital, in which changes are in steps).
Analog control - A method using continuously varying voltage levels to provide control of equipment.
Analog Sunset - A colloquial term associated with conversion from analog television broadcasting to digital television. Because of the vast number of analog television sets in use worldwide, and the time required for consumers to replace them with sets capable of receiving digital transmission, communications management and policy agencies, such as the US Federal Communications Commission and its global counterparts, have established a multiple-year transition period for this process. It is this transition period which is considered the “analog sunset.”
Anamorphic - A type of lens or adapter designed to produce a widescreen image from a condensed image on the film. Trademarked anamorphic systems include CinemaScope, VistaVision, and Panavision.
Anamorphic DVD - A DVD with a widescreen video image that has been horizontally squeezed to fit into a standard video frame, resulting in an image with higher resolution than letter boxing can produce. Anamorphic DVDs are designed for optimal display on 16:9 widescreen displays or video scalers with an anamorphic squeeze mode.
Anechoic chamber - An acoustic space without echo or reverberation. Often used for the acoustic testing of microphones and loudspeakers.
Angle of Incidence - The angle between a ray incident on a surface and the line perpendicular to the surface at the point of incidence, called the normal.
Angled Physical Contact – APC - A specific technique for single-mode fiber applications where the endface of the fiber or ferrule is cut and polished at an 8 degree angle in order to increase contact surface area and help minimize return loss.
ANSI lumen - The common unit of measurement for the light output of a projector, as measured by ANSI, the American National Standards Institute. The higher the ANSI lumen rating, the brighter the projector. In general, there needs to be about a 30% differential in the ANSI lumen rating before the human eye can really notice an appreciable difference in brightness when two projectors are shown side by side. Determining the lumen output for a given application depends on five factors, (1) the level of ambient room light (2) the size of the audience, (3) the size of the projected image, (4) the quality of the projection screen, and (5) the amount of detail in the presentation material. See “Lumen.”
Antialiasing - A technique in computer graphics for smoothing jagged edges by blending shades of color or gray along the edges. Some video devices, such as character generators, have an antialiasing feature to minimize aliasing through filtering and other techniques. See “Aliasing.”
Aperture - The opening, usually an adjustable iris, that controls the amount of light passing through a lens. In motion picture cameras, the mask opening that defines the area of each frame exposed. In motion picture projectors, the mask opening that defines the area of each frame projected.
Aperture grill - A grill-like feature of Sony Trinitron CRT monitors and others licensed by Sony that controls the number of electrons hitting the phosphor coating on the screen.
Apple Cinema Display - One of the first very high resolution monitors on the market and one of the first to utilize a dual-link DVI connection. The 30” version provides a native resolution of 2560x1600 pixels.
Aramid Yarn - A woven strength member, with Kevlar® as a common brand, incorporated into fiber optic cable that provides tensile strength and protection.
Arc - In fiber optics, the discharge that may occur between the two electrodes of a fusion splicer.
Armored Cable - Cable that is protected with metal sheathing or rods below or between the cable jacketing to protect from damage due to adverse outdoor factors such as rodent attack.
ARP - Address Resolution Protocol. A protocol for assigning an IP address to a device based on the device’s MAC (Media Access Control), or physical machine address, that maintains a table showing the correlation between the two.
Artifacts - Visible corruption of the image or undesirable elements or defects in a video picture. These may occur naturally in the video process but must be eliminated to produce a high quality picture.
ASCII - American Standard Code for Information Interchange. The standard code consisting of 7-bit coded characters (8 bits including parity check) used to exchange information between data processing systems, data communication systems, and associated equipment. The ASCII set contains control characters and graphic characters.
Aspect ratio - The relationship of the horizontal dimension to the vertical dimension of an image. In viewing screens, standard TV is 4:3, or 1.33:1; HDTV is 16:9, or 1.78:1. Sometimes the “:1” is implicit, making TV = 1.33 and HDTV = 1.78.
ASTA - Active Sync Termination Adapter. A VGA-style (15-pin HD connector) adapter that provides active circuits that shape up the horizontal and vertical sync signals. This adapter may be used to eliminate jitter and/or intermittent tearing in the displayed image. Most small digital projectors are designed to be near the video source and may not provide impedance matching.
Asynchronous - Intermittent, not synchronized or continuous. A conversational type of communication that allows the parties at each end to talk when they like instead of at a prescribed time. Used in videoconferencing.
ATM - Asynchronous Transfer Mode. In videoconferencing, a system for transmission and switching of digital signals through the telephone system. See Asynchronous.”
ATSC - Advanced Television Systems Committee. The ATSC was formed to establish voluntary technical standards for advanced television systems, including digital high definition television (HDTV). The ATSC is supported by its members, who are subject to certain qualification requirements.
Attenuate/Attenuation - To reduce the amplitude (strength) or current of a signal.
Attenuation - In fiber optics, this is the loss of optical power as light passes through a fiber optic path. This loss can occur due to absorption, scattering, and excessive bending within the fiber, and can also be attributed to optical components such as connectors, splices, and splitters. Attenuation is usually expressed in dB/km.
Audio - Of or concerning the electronic transmission of sound, specifically the electrical currents representing a sound. (CF. Sound)
Audio follow - A term used when audio is tied to other signals, such as video, and they are switched together. The opposite of “breakaway.”
Audio frequency - Frequencies within the range of human hearing, about 20 Hz to 20 kHz.
Audio summing amplifier - A device that converts two-channel stereo audio signals into balanced/unbalanced one-channel mono audio signals.
Auto-focus - Automatic focus. A device in a projector or camera that uses light reflected from a surface to focus the image.
AutoImage™ - An Extron technology for scan converters and signal processors that simplifies setup by executing image sizing, centering, and filtering adjustments with a single button push.
Auto-input switching - The feature that enables a product to detect which input has an active sync signal and switch to that input.
Automatic convergence - The automatic alignment of the red, green, and blue color images on a screen.
Automatic sync stripping - The automatic removal of sync signals from video channels. Typically, this is associated with removing the sync signal from the green channel, but it may apply to stripping the sync from all three video channels (Red, Green, and Blue).
Autosizing - Automatic picture sizing adjustment to compensate for different display modes, thus enabling the display system to center the picture and fill the screen.
Autoswitching - The feature that enables a product to detect which input has an active sync signal and switch to that input.
Avalanche Photodiode – APD - A type of photodiode, or optical signal transducer that converts light to an electrical signal, used in fiber optic receivers.
AWG - American Wire Gauge. A standard measurement for wire conductor diameter.
Back porch - The time in a composite video signal that is between the trailing edge of the sync pulse and the trailing edge of the blanking pulse (before the video information). See “Blanking.”
Backbone - The primary transmission network for telecommunications that connects between key locations and branches off to buildings and other facilities.
Backreflection - Light within an optical fiber that is reflected back toward the source. This typically occurs at interfaces between the fiber and the connector where an air gap causes the reflection.
Backscattering - The portion of light within an optical fiber that is scattered back toward the source.
Balanced audio - The audio signal that is carried on three wires (or five wires for stereo pair), with two of them carrying the same signal but with reversed polarity, and a third wire for shielding. Since the two signal wires would pick up virtually identical noise from outside (common mode noise), and that noise can be canceled out at the receiving end by a differential amplifier, the balanced audio is much less susceptible to hum and interference from long cable runs.
Band reject filter - A filter that combines the characteristics of a low pass and a high pass filter that is used to block a narrow band of frequencies, while allowing frequencies above or below this band to pass. (i.e. notch filter)
Banding - A video problem of dark bars appearing across the displayed image in areas where there is movement.
Bandpass filter - A filter that allows a specific range to pass. The bandpass frequencies are normally associated with frequencies that define the half power points, i.e. the -3 dB points. In multi-driver speaker systems, for example, the mid-range driver may be fed by a bandpass filter.
Bandwidth - The total range of a frequency required to pass a specific signal without significant distortion or loss of data. In analog terms, the lower and upper frequency limits are defined as the half power, or -3 dB signal strength drop, compared to the signal strength of the middle frequency, or the maximum signal strength of any frequency, expressed as xx Hz to xx kHz (or MHz) @ -3 dB. In digital terms, it is the maximum bit rate at a specified error rate, expressed in bits per second (bps).
Barrel connector - An adapter used to connect two coax-type connectors of the same gender.
Baseband - A prime signal such as composite video, component video, and audio with its own path but is not modulated onto a carrier signal or combined with other signals on a path. An unmodulated signal or band of signals. The video signal seen on a waveform monitor is a baseband video signal.
Baud - Named for J. M. E. Baudot, the inventor of the Baudot telegraph code. The number of electrical oscillations per second, called baud rate. Related to, but not the same as, transfer rate in bits per second (bps).
Bend Loss - In fiber optics, the attenuation of light as it passes through a fiber with excessive bending. Macrobending and microbending both contribute to bend loss.
Bend radius - The smallest radius at which an optical fiber or fiber optic cable can be bent without introducing attenuation or damage to the fiber.
Bending - A video problem when the top of the screen hooks, bends, or tears to the side. Also known as “hooking.”
Bidirectional - When signals can pass in either direction through the same port or by the same path. RS-232 communications are bidirectional because the devices at either end can transmit and receive.
Binary - A numbering system using base-2. Each digit is represented by a 1 or a 0 (on or off).
Binary code - A coding system using the digits 0 and 1 to represent a letter, numeral, or other character in a computer. For example: the character “A” in ASCII code becomes 0100 0001 in binary.
B-ISDN - Broadband Integrated Services Digital Network. A special version of ISDN that uses fiber optics and can transfer at 1.5 megabits per second. Also see “Integrated Services Digital Network (ISDN).”
Bit - The shortened form of “binary digit” (0 or 1). A bit is the smallest unit of information in a computer.
Bit depth - The number of bits per pixel. Bit depth determines the number of shades of gray or variations of color that can be displayed by a computer monitor. For example, a monitor with a bit depth of 1 can display only black and white; a monitor with a bit depth of 16 can display 65,536 different colors; a monitor with a bit depth of 24 can display 16,777,216 colors
Bit Error Rate – BER - The fraction of bits that were transmitted with errors, expressed at the ratio of incorrectly to correctly transmitted bits. BER is used to assess transmission accuracy in a fiber optic system.
Bit map - A method of graphic display using rows and columns of dots, or pixels. Each pixel location corresponds to a specific location in memory.
Bit Rate - The rate of digital data transmission, commonly expressed in bits per second–bps, kilobits–kbps per second, Megabits per second–Mbps, and Gigabits per second–Gbps.
Black - The darkest visible surface created by the absorption of all incident light and color. In video, the absence of picture information.
Black and white - Monochrome (one color) or luma information. In the color television system, the black and white portion of the picture has to be one color: gray, D6500 or 6500° K, as defined by x and y values in the 1939 CIE color coordinate system. Commonly referred to as “D65.”
Black level - More commonly referred to as “brightness,” the black level is the level of light produced on a video screen. The level of a picture signal corresponding to the maximum limit of black peaks. The bottom portion of the video wave form, which contains the sync, blanking, and control signals. The black level is set by the brightness control.
Blackburst - The video waveform without the video elements. It includes the vertical sync, horizontal sync, and the chroma burst information. Blackburst is used to synchronize video equipment to align the video output. One signal is normally used to set up an entire video system or facility. Sometimes it is called House sync.
Blackburst generator - A special device for calibrating video equipment by generating a composite video signal with a totally black picture. This blackburst signal is used to synchronize video equipment to provide vertical interval switching. It also provides black level and chroma burst information for maintaining uniform video levels and color information.
Blanking - The interval after the electron beam completes a scan line and returns (retraces) to the left. During this time, the beam must be turned off (horizontal blanking). Similarly, when the last line has been scanned at the bottom of the screen, the beam must return to the upper left (vertical blanking).
Blanking adjustment - The ability to adjust the degree of blanking on the image. This is useful for eliminating artifacts such, as closed caption noise or improperly adjusted VTR head-switching that can be seen at the top or bottom of a displayed image.
Blanking level - The level of a video signal that separates the picture information from the sync information. The level of the front and back porches is 0 IRE units. To blank the video signal, the video level is brought down to the blanking level so nothing is visibly displayed, while the electron beam returns (retraces) to the start of the next line.
Blooming - Most noticeable at the edges of images on a CRT, blooming is when the beam hitting the screen is too intense and overdrives the phosphors. The edges of an image seem to exceed its boundaries. Thin lines and sharp edges may look thick and fuzzy. This may be caused by the contrast being set too high, or by a high voltage problem.
Blu-ray Disc - An optical disc storage medium developed by Sony as the replacement for DVD. Bluray is capable of storing high-definition video, audio, and data with a capacity of 50GB per disc. Blu-ray players are backward-compatible with standard DVDs and audio CDs.
BME - Basic Module Enclosure. Some large devices, such as the Extron Matrix 3200/6400/12800 Switchers, may be contained in more than one enclosure, yet function as a single device. Each physical box, or enclosure, is called a BME.
BNC - Bayonet Neill-Concelman. A cable connector used extensively in television and named for its inventors. A cylindrical bayonet connector that operates with a twist-locking motion. To make the connection, align the two curved grooves in the collar of the male connector with the two projections on the outside of the female collar, push, and twist. This allows the connector to lock into place without tools.
Boot/Boot-up/Bootstrap - The initialization process a system goes through after power comes on. It may also occur as part of resetting. To start a new beginning, you “pull yourself up by your bootstraps.”
Bow - The curving of scan lines in the center of the image.
Breakaway - The ability to separate audio and video signals for switching them independently. For example, the audio and video signals from one source may break away and be switched to two different destinations. This is the opposite of the term “audio follow.”
Breakdown voltage - The voltage level at which the insulation between conductors fails and electricity flows between the conductors.
Breakout Cable - In fiber optics, a cable comprising a bundle of several jacketed fibers, with the fibers separated from the bundle at one end to facilitate installation into panels and other equipment. The fibers are individually jacketed.
Breakout Kit - In fiber optics, a kit used to create a breakout cable from bundled fiber optic cable.
Breezeway - The early part of the back porch portion of the video signal. The area between the horizontal sync pulse and the color burst.
Bridge (or multipoint bridge) - A device that allows multiple systems to dial in and participate in a single videoconference.
Bridging (or Bridged) - Audio Some stereo amplifiers are designed to allow “bridging” or combining the power output of two channels into one channel. Bridging allows the amplifier to drive one speaker with more power than the amp could produce for two speakers. Not all amplifier designs allow bridging, however. NEVER attempt bridging of an amplifier without first consulting the manufacturer’s documentation and instructions.
Brightness - Usually refers to the amount or intensity of video light produced on a screen without regard to color. Sometimes called “black level.”
Brightness control - The control on a television monitor that increases or decreases the radiance of an image.
Brightness ratio - The difference between the lightest (whitest) and darkest (blackest) areas in an image. The
wider the brightness ratio, the wider the contrast ratio.
Brightness signal - Same as the luma (Y) signal; a signal that carries information about the light intensity at each point in the image.
Broadband - A communications channel that has greater bandwidth than a voice-grade line and is capable of greater transmission rates.
Buffer - Generally referred to as a unity gain amplifier, a buffer is used to isolate the signal source from the load. A buffer can be used for digital or analog signals.
Buffer Coating - A plastic coating applied to an optical fiber that provides protection from moisture or damage, as well as handling during the manufacturing of fiber optic cable.
Buffer Tube - An additional plastic tubing around the buffer coating of an optical fiber that provides added protection. This tubing is typically colored.
Burn-in - In a video or plasma display, this term describes what happens when an image has been displayed too long, a permanent image is burned into the screen phosphor.
Bus - A path for transporting voltages, signals, or a ground between the different sections of an electronic device, such as a data bus between a CPU and memory or a peripheral device. Its width is determined by the number of lines (conductors) that make up the bus, and its speed (data transfer rate) is determined by the circuits that drive the lines.
Butt Closure - A product that serves to provide protection to fiber optic cable splices and terminations within a sealed enclosure.
Butterworth filter - A filter characterized by smooth response at all frequencies and -6 dB per octave decrease from the specified cutoff frequencies. Butterworth filters are maximally flat; that is, they pass the selected band of frequencies (the pass band) without distortion.
Cable equalization - The method of altering the frequency response of a video amplifier to compensate for high frequency loss in cables that it feeds. Also see “Peaking.”
Cable Jacket - The outer protective covering of wire or fiber optic cable.
CAD - Computer Aided Design. The use of the computer system for designing, such as in architectural and engineering applications.
Candela - Derived from the word “candle” and denoted by the symbol “cd”, the candela is the standard unit of light intensity. One candela is roughly equal to the amount of light, in any direction, from the flame of a candle. The luminance of a light source is often expressed in candelas per square meter (cd/m2).
Capacitance - The ability to store an electrical charge.
Capacitor - A device made up of one or more pairs of conductors, separated by insulators and capable of storing an electrical charge. When there is a difference of potential between the conductors, and because current cannot flow through the insulator, an electrical charge is stored.
Captive screw connector - A connector that uses a screw to hold a stripped wire end.
CAT 5 - Category 5. Describes the network cabling standard that consists of four unshielded twisted pairs of copper wire terminated by RJ-45 connectors. CAT 5 cabling supports data rates up to 100 Mbps. CAT 5 is based on the EIA/TIA 568 Commercial Building Telecommunications Wiring Standard.
CAT 5e - Enhanced Category 5. The standard for the next higher grade of unshielded twisted pair (UTP) beyond Category 5. The CAT 5e specification was developed to provide more robust support for 1000Base-T. CAT 5e specifies tighter limits than CAT 5 for NEXT, ELFEXT, and return loss.
CAT 6 - Category 6. The standard for the next higher grade of unshielded twisted pair (UTP) cabling beyond CAT 5e. The standard defines components (cable and connecting hardware) and cabling (basic link and channel) for Category 6 channels, as well as Level III field tester requirements.
CAT 7 - Category 7. The cable standard for 10 Gigabit Ethernet using shielded twisted pair (STP) cable. Cat 7 features strict guidelines for crosstalk and system noise, requiring shielding for each pair of wires and the cable as a whole.
CCD - Charge Coupled Devices. A light-detecting circuit array used in video cameras, scanners, and digital still cameras.
CCIR - Comite Consultatif International des Radio-Communications, the International Radio Consultative Committee. The CCIR has been superseded by the International Telecommunications Union, or ITU. See “ITU.”
CCIR 601 - See “ITU-R BT.601.”
CCITT - French term for Consultative Comit? of International Telephone and Telegraph, the international group that sets standards for telephony and digital communications (e.g., H.320 — the audio and video codecs and protocol for ISDN).
CCTV - Closed Circuit Television. A distribution system that limits reception of an image to those receivers that are directly connected to the origination point by coaxial cable or microwave link.
CE - Conformit Europenne. A label or mark on a product signifying ESD, EMI, and safety compliance with all European Union (EU) directives applicable to that product. Some interpret it to mean European Community or Compliance for Europe.
CEC – Consumer Electronics Control - A bidirectional serial control bus defined in the HDMI 1.0 specification and subsequent updates. CEC is used to provide control for multiple products, connected via HDMI cables, from a single remote control. Alternately, one device, for example a Blu-ray Disc player, can turn on another device, such as a display, when put into Play mode. CEC command sets are proprietary to each manufacturer; Sony CEC commands cannot control devices from Panasonic or Sharp, and vice versa.
CEDIA - Custom Electronic Design and Installation Association. CEDIA is an international trade association of companies specializing in planning and installing electronic systems for the home. This association offers an annual expo.
CENELEC - European Committee for Electro-technical Standardization.
CGA - Color Graphics Adapter. Introduced in 1983, it was IBM’s first product to display both color and graphics. CGA has a horizontal scan frequency of 15.75 kHz and a vertical frequency
of 60 Hz.
Chroma - (chroma signal) (1) Hue and saturation are qualities of chroma. Chroma does not include black, gray, or white. The purity or intensity of color, sometimes called “hue.” Color information, independent of luma intensity or brightness. Without the chroma signal, the video picture would be black and white. (2) The NTSC or PAL video signal contains two parts that make up what you see on the screen: the black and white (luma) part, and the color (chroma) part.
Chroma burst - See “Color burst.”
Chroma crawl - An artifact of encoded video also known as dot crawl or cross-luma. It occurs in the video picture around the edges of highly saturated colors as a continuous series of crawling dots (“dancing ants”) and is a result of color information being confused with luma information by the decoder circuits.
Chroma delay - A video problem in which the color of an object or area is shifted slightly to the right of the luma (intensity).
Chroma gain (chroma, color, saturation) - In video, the gain of an amplifier as it pertains to the intensity of colors in the active picture.
Chroma key (color key) - A film and video process in which the subject is filmed in front of a blue or green background (the key color). For example, a weather reporter stands in front of a blue wall with a camera focused on him or her. The camera’s video signal feeds into a chroma keyer, which detects the blue background and replaces it with a video signal from another source, such as video of a weather map. Thus, the reporter appears to be standing in front of the weather map.
Chromatic Dispersion – CD - In fiber optics, a factor that reduces fiber bandwidth as a result of the separation of the incoming light into components of various wavelengths, which travel at different speeds along the fiber. This effect is associated with single-mode fiber at very long distances.
Chrominance - See “Chroma.” CIE Commission Internationale de l’Eclairage (the International Commission on Illumination). CCIR is the organization responsible for the chroma diagram of 1939, a three dimensional diagram that defines light and color. Other systems have been developed by CIE more recently.
Cladding - In fiber optics, the outer layer surrounding the core of a fiber that serves as an optical barrier as well as protection for the core. The index of refraction for the cladding is always lower than that for the core in order to maintain total internal reflection and thus ensure that the light travels within the core.
Class A - The output transistor(s) always have current flowing through them. This method of operation is pure, but inefficient. Class A amplifiers rarely exceed 20% efficiency in terms of power consumed (converted to heat) versus power delivered to the load.
Class A/B - A combination of Class A and Class B amplifier designs that corrects the inefficiency of Class A amplifier designs and allows a small amount of current to continually flow through the output transistors at all times. This alleviates most of the cross-over distortion at the expense of efficiency. An A/B amplifier is still more efficient (60 to 65%) than a Class A amplifier.
Class B - Somewhat more efficient than Class A. Class B amplifiers utilizing two drive elements operating in a push-pull configuration. On the positive excursion of the signal, the upper element supplies power to the load while the lower is turned off. During negative going signal excursions, the opposite operation occurs. This increases operating efficiency, but the exchange from ON to OFF causes a switching error condition commonly called cross-over distortion.
Class D - Also known as a switching amplifier, Class D amplifiers utilize output transistors which are either completely turned on or completely turned off (they’re operating in switch mode). Class D amplifiers operate either in the fully ON-region or fully OFF-region. Class D amplifiers reach efficiencies as high as 90%. This is of great importance to portable applications relying on battery power and for the lowest production of heat.
Cleave and Crimp - In fiber optics, the utilization of pre-polished connectors to significantly reduce termination time by eliminating the most time consuming step – polishing the connectors, so that the process requires just cleaving the fiber, insertion into the connector, and crimping.
Cleave Tool - Also known as a scribe tool, this specialized tool is used to break off a portion of an optical fiber by scoring, or scribing the fiber so that it can be cut using a cleaver to ensure a clean, precise, cut with the endface flat and at a 90-degree angle to the fiber axis.
Cleaving - The process of cutting the end of an optical fiber after it has been scored, or scribed using a cleave or scribe tool. The cut is made at a precise 90 degree angle to the fiber axis.
Client - A computer or network device that uses information supplied by a server.
Cliff effect - The sudden loss of a digital signal at the receiver. In the analog domain, video quality will gradually degrade as signal strength is lost, resulting in a “snowy” but discernable image on screen. With digital signals, the image is either perfect or non-existent. When the quality of a signal falls below the threshold over which the receiver can correct or recover it, the screen goes blank and the signal is said to have “fallen off the cliff.”
Clipping - Cutting off the peaks (or excursions) of a signal. A form of distortion that occurs when the signal excursions exceed the limits of the circuit.
Clipping level - An electronic limit to avoid overdriving an audio or video signal.
Clock rate - The rate at which analog audio is sampled and converted to a digital signal. Clock rate is important in digital audio recording and processing systems. When samples are not output at the correct time relative to other samples, a condition called “clock jitter” occurs. Clock jitter can also arise when digital audio is run through several audio products. When each product runs on its own clock, compensating for small differences between the clocks can cause output errors. For instance, even if both clocks are at exactly the same frequency, they will almost certainly not be in phase. If the clock rate of the input digital stream and the playback unit differ (44.1 KHz and 48 KHz, for instance), the playback unit has no choice but to perform a sample rate conversion. If they are the same, the playback unit may use sample rate conversion to oversample the input (for example, 88.2 or 96 kHz), then pick the samples that “line up” with its own clock.
CMR - Common Mode Rejection. A measure of how well a differential amplifier rejects a signal that appears simultaneously and in phase at both input terminals. As a specification, CMR is expressed as a dB ratio at a given frequency.
CMRR - Common Mode Rejection Ratio. (1) For a differential amplifier, the ratio of the differential gain to the common mode gain. (2) Expressed in dB, it is the ratio of common mode input voltage to output voltage. (3) For an operational amplifier, the ratio of the change in input offset voltage to the change in common mode voltage.
CMYK - Cyan, Magenta, Yellow, and Black. See “Subtractive color.”
Coarse Wavelength Division Multiplexing – CWDM - The multiplexing, or combining of several wavelengths into a single optical signal. CWDM is distinguished from Dense Wavelength Division Multiplexing – DWDM in that the separation between wavelengths – 20 nm – is much greater.
Coating - A layer of plastic covering over the fiber to provide protection from moisture as well as damage in manufacturing fiber optic cables. Also known as a buffer coating.
Coaxial cable - A two-conductor wire in which one conductor completely wraps the other, with the two separated by insulation. Constant impedance transmission cable. Example: 75 ohm, type RG-59 cable used for video signals. Abbreviated as coax.
Coaxial speaker - A type of speaker design in which a high frequency driver (typically a tweeter) is placed inside a low or mid frequency driver.
CobraNet - A trademark of Peak Audio, CobraNet is network technology for the transmission of digital audio, video, and control signals over 100Mbps Ethernet networks.
Codec - (1) Coder/decoder. A device that converts analog video and audio signals into a digital format for transmission over telecommunications facilities and also converts received digital signals back into analog format. It may also dial up the connection, like a modem for teleconferencing. (2) Compressor/decompressor. Codecs can be implemented in software, hardware, or a combination of both. Some popular codecs for computer video include MPEG, QuickTime, and Video for Windows.
Collision - When signals from two or more connected devices on a network attempt to transfer simultaneously and crash into each other. Common on Ethernet systems.
Color adjustment - A video adjustment that is used to control color or chroma intensity.
Color bars - A standard test pattern of several basic colors (white, yellow, cyan, green, magenta, red, blue, and black) as a reference for system alignment and testing. In NTSC video, the most commonly used color bars are the SMPTE standard color bars. In PAL video, the most commonly used color bars are eight full field bars. In the computer, the most commonly used color bars are two rows of reversed color bars.
Color black - The NTSC standard for black, which is 8% gray. Computer black, the absence of all of the color primaries, is referred to as superblack and is used for matting or keying in video effects. Superblack does not render well to video. Instead of appearing black, it has a light gray appearance. Color black will appear blacker on video than superblack.
Color burst - In color TV systems, a burst of subcarrier frequency located on the back porch of the composite video signal. This serves as a color synchronizing signal to establish a frequency and phase reference for the chroma signal. Color burst is 3.58 MHz for NTSC and 4.43 MHz for PAL.
Color encoder - A device that combines the separate red, green, and blue signals into one composite video signal.
Color phase - The timing relationship of the color video signal. The correct color phase will produce the correct color hues.
Color resolution - The number of colors available at one time in an image, measured in terms of bits per pixel.
Color space - A model of the color spectrum with the order of colors defined by three parameters in a 3D space: intensity, saturation, and hue. There are several color space definitions, each used to support the specific identity of colors within a structured identification system. In A/V presentation, there are two primary video color space definitions: RGB, which describes the three color primaries, Red, Green, and Blue; and Component or YUV, which describes the luminance channel (Y) and two chrominance channels, U (Blue minus Y) and V (Red minus Y), with the remainder representing Green. RGB is most commonly used with high-resolution computer video signals, while YUV is the primary color space for motion video and television transmission because it requires less bandwidth. Digital standards such as DVI, HDMI, and DisplayPort support both RGB and YUV color space, and color space conversion is common in sources such as Blu-ray Disc players and both flat panel and projection display devices. Color space and color space conversion pose a unique challenge when switching between signals
Color subcarrier - The carrier signal or frequency on which the color signals are modulated. The most commonly used color subcarrier frequency is 3.58 MHz for NTSC, and 4.43 MHz for PAL.
Color temperature - The color quality, expressed in degrees Kelvin (K), of a light source. The higher the color temperature, the bluer the light. The lower the temperature, the redder the light. Benchmark color temperatures for the A/V industry include 5000° K (a comparatively “warm” or reddish color temperature, favored for pleasing video reproduction); 6500° K (D65, the reference color for accurate color reproduction); and 9000° K (a comparatively “cold” or bluish color temperature, favored for graphics and other high-contrast image reproduction).
Comb filter - A filter circuit that passes a series of frequencies and rejects the frequencies in between, producing a frequency response that resembles the teeth of a comb. This is an improvement over the notch filter. Its precise separation of the chroma and luma reduces both cross chroma and cross luma artifacts (chroma crawl or zipper artifacts). It preserves more detail in black and white, resulting in a better quality picture. Although comb filters are successful in reducing artifacts, they may also cause a certain amount of loss of resolution in the picture.
Combing - An undesirable blurring of an image that contains motion. This effect occurs when a single frame of video combines two fields of video derived from different frames of film.
Component digital - Digital video using separate color components, such as Y, Cb, Cr. Digital recording formats such as D1 (Sony, BTS/Philips) and D5 (Panasonic) utilize component digital recording technology. Component digital is the digital representation of the component analog signal set, Y, B-Y, R-Y; it is often represented as 4:2:2. The encoding parameters are specified by ITU-R BT.601-2 (formerly known as CCIR 601).
Component video - Color television systems start with three channels of information: red, green, and blue (RGB). In the process of translating these channels to a single composite video signal, they are often first converted to Y, R-Y, and B-Y. Both three-channel systems, RGB and Y, R-Y, B-Y, are component video signals. They are the components that eventually make up the composite video signal. Higher quality program production is possible if the elements are assembled in the component domain.
Composite digital - Digital video that is essentially the digitized waveform of NTSC or PAL video signals, with specific digital values assigned to the sync, blank, and white levels. Commonly described as “4fsc”, a sampling rate locked to four times the frequency of color subcarrier. Early digital tape formats, such as D2 (Sony) and D3 (Panasonic), used a composite digital recording scheme. Also refers to digitally encoded video signal, such as NTSC or PAL video, that includes horizontal and vertical synchronizing information.
Composite sync - A signal combining horizontal and vertical sync pulses and equalizing pulses with no picture information and no signal reference level. Composite sync is sometimes referred to as “C”, “S” (as in RGBS), or “HV” (as on some connector panels).
Composite video - An all-in-one video signal comprised of the luma (black and white), chroma (color), blanking pulses, sync pulses, and color burst.
Compression - A process in which the digital data is reduced to meet bandwidth requirements, while at the same time without negatively affecting the capability to convey image, video, or audio information, or the contents of a data file.
Compression artifacts - Compacting of a digital signal, particularly when a high compression ratio is used, may result in small errors when the signal is decompressed. These errors are known as artifacts, or unwanted defects. The artifacts may resemble noise or may cause parts of the picture, particularly fast moving portions, to be displayed as distorted or incomplete. Typical artifact types include “mosquito wings” and “blocking.”
Compression connector - A special connector, such as a BNC, RCA, or F-Connector, that is quickly and securely attached to a cable by using a compression tool. The connector is compressed onto the cable. See “Compression tool.”
Compression tool - A special cable tool that is used to quickly and securely attach a connector, such as a BNC, RCA, or F-Connector, by compressing the connector to the cable. See “Compression connector.”
Computer-video interface - A device that converts the nonstandard video output of computer systems to a standard RGB analog signal, which can then be connected to a compatible data monitor and projector.
Constant voltage system - The common name given to the interface between amplifiers and speakers in a distributed audio system. Several voltages are used, but the most common are 70.7 V (commonly shortened to 70 V) in the US, and 100 V in Europe. “Constant voltage” refers to the characteristic that whether the total output of the amplifier is 5 watts or 50 watts or 500 watts, the maximum output voltage is always a constant of 70.7 V. The voltage stays the same regardless of the load, so the output current varies but not the voltage.
Contact closure - The momentary connection of two conductors to complete an electrical circuit. Often used to switch inputs on switchers.
Continuity - In digital picture manipulators, the characteristic of location/positioning that determines if the motion path continues smoothly.
Continuous power - The continuous power specification can be used to describe the output of an amplifier and is typically stated at “x watts (rms) into y ohms from 20 Hz to 20K Hz at z% THD (total harmonic distortion)”. For example, the Extron MPA 122 amplifier is specified as 11 watts (rms) per channel into 4 ohms at 1% THD.
Continuous presence - A feature in some videoconferencing equipment that allows the participants to view multiple sites on the same video screen. This is a function of the codec used and not of the video switching system.
Contouring - Digital video picture defect caused by quantizing at too coarse a level.
Contrast - The range of light and dark values in a picture, or the ratio between the maximum and the minimum brightness values. Low contrast is shown mainly as shades of gray, while high contrast is shown as blacks and whites with very little gray. It is also the name of a TV monitor adjustment, which increases or decreases the level of contrast of a displayed picture. Also called “white level.”
Contrast range - The range of grays in a video image.
Contrast ratio - The ratio of the high light output level divided by the low light output level. In theory, the contrast ratio of the television system should be at least 100:1, if not 300:1. In reality, there are several limitations. In the CRT, light from adjacent elements contaminates the area of each element. Room ambient light will contaminate the light emitted from the CRT. Well-controlled viewing conditions should yield a practical contrast ratio of 30:1 to 50:1.
Convergence - The alignment of the red, green, and blue video projected onto a screen when the lines produced by the three color sources appear to form one clearly focused white line. The point at which the light from each of the three lenses aligns so the perceived single image is clearly focused. Lack of convergence is a video problem when the displayed image appears to be outlined by red, green, or blue because of misaligned colors.
Core - The central core of an optical fiber in which the light travels. The core’s index of refraction is always greater than that of the cladding which surrounds it, to maintain total internal reflection and therefore keep the light within the core.
Coupling Loss - The loss of optical power as light passes through a junction, expressed as the ratio of the optical power measured at the junction, such as a coupler, to the total optical power entering the system.
Crest factor - The ratio of peak value of a signal divided by the rms value of the signal. The crest factor of the audio program determines the required headroom needed in the audio system.
Critical Angle - An important angle of incidence for light as it meets a boundary between two refractive materials. Above this angle, total internal reflection occurs. In an optical fiber, light that strikes the boundary between the core and cladding greater than the critical angle is internally reflected within the core as it travels along the fiber.
Cross color - Moir or rainbow artifacts in an encoded video picture caused when the video encoder or decoder misinterprets luma detail as color information, resulting in color being displayed where it shouldn’t be. It is especially noticeable when the subject wears pinstriped clothing.
Cross luma - Dot crawl, chroma crawl. A video artifact that occurs when a composite video decoder incorrectly interprets chroma information (color) to be high-frequency luma information (brightness). This may appear as tiny, colored dots that creep along the edges of objects.
Crosshatch - A test pattern consisting of vertical and horizontal lines used for converging a color display device.
Crossover distortion - A type of distortion that occurs in push-pull class AB or class B amplifiers. It happens during the time that one side of the output stage shuts off, and the other turns on.
Crossover network - An electrical circuit that combines high pass, low pass, and bandpass filters to divide the audio frequency spectrum, 20 to 20,000 Hz, into ranges suitable for low frequencies (woofer), mid-range, and high frequencies (tweeters).
Crosspoint - An electronic switch, usually part of an array of switches that allows video or audio to pass when the switch is closed.
CrossPoint - The name for Extron wideband and ultra-wideband, RGBHV matrix switchers.
Crosstalk - Caused by interference between two signals, usually from an adjacent channel, which adds an undesired signal to the desired signal. Crosstalk is caused by magnetic induction or capacitive coupling, and can occur when there is a grounding problem or improper cable shielding. Video symptoms include noise and ghosting, while audio symptoms include signal leakage.
CRT - Cathode Ray Tube. A vacuum tube that produces light when energized by the electron beam generated inside the tube. A CRT has a heated cathode and grids in the neck of the tube, making up the gun. Electrons are accelerated from the gun toward the front surface of the tube (screen), producing a beam. The surface on the back of the screen is coated with phosphors that light up when struck by the electron beam. The CRT in a TV is known as the picture tube. Some CRTs have three guns—for red, green, and blue colors.
CTS - Certified Technology Specialist. An A/V and video professional who, through practical experience and extensive industry training programs offered by ICIA, has developed a high level of expertise.
Curing Oven - A specialized oven used to thermally cure epoxy for adhering a fiber optic connector ferrule onto the optical fiber.
Current - The flow of electricity, and the rate at which it flows. See “Amp.”
Cut - An instantaneous transition between two sources. An instantaneous scene change.
Cutoff Wavelength - In single-mode optical fiber applications, the wavelength below which the fiber transmits as multimode instead of single-mode.
D connector - A connector with rounded corners and angled ends, taking on the shape of the letter D. Commonly used in computers and video, most D connectors have two rows of pins. If they have more than two rows, they are usually called HD (High Density) connectors.
D/A - Digital to analog.
D1 - A component digital recording format that conforms to the ITU-R BT.601 standard, using 19mm tape, uncompressed. Though largely obsolete as a digital recording format, “D1” is commonly used to describe component digital video utilizing a 4:2:2 (Y Cb Cr) signal structure.
D5 - A component digital videotape recording format that conforms to ITU-R BT.601 standard, using 1/2” tape, 10 bits video coding, uncompressed. The primary manufacturer is Panasonic.
D9 - A component digital videotape recording format that conforms to ITU-R BT.601 standard, using 1/2” tape, eight bits, 3:1 compressed. Previously called Digital-S. The primary manufacturer is JVC.
DA - Distribution amplifier. A device that allows connection of one input source to multiple, isolated (buffered) output destinations such as monitors or projectors.
DAC - Digital to analog converter.
Damping factor - The measurement of a power amplifier’s ability to control the motion of a speaker’s cone after a signal disappears. The higher the number, the better the damping factor.
Dark Fiber - A term in fiber optics to denote fiber that is installed at a facility but reserved for future use.
DAT - Digital Audio Tape. A method developed by Sony and Hewlett-Packard for recording large amounts of information in digital form on a small cassette tape.
Data - (1) A representation of facts, concepts, or instructions in a format suitable for communication, interpretation, or processing by human or automated means. (2) Any representations, such as characters or analog quantities, that have meaning.
Data Compression - A mathematical algorithm for compressing or encoding data to fit within given bandwidth requirements for transmission or storage.
Data Link - A fiber optic system comprising the cable, transmitter, and receiver for transmission of data between two locations.
dB (Decibel) - The standard unit used to express gain or loss of power between two values. A decibel is 10 times the logarithm of a ratio of two power values. When comparing voltage or pressure, the values in the ratio are squared or the log is multiplied by 20 instead of 10. An extension is placed behind the ‘dB’ when one of those values is a fixed reference (i.e. dBV, dBu, dBSPL).
dB per octave - How quickly a crossover or filter attenuates signals (decreases their power) outside its passband (those frequencies intended to pass through without attenuation); expressed in decibels per octave. Crossover and filter slopes are designed as first order (attenuates signals slowly, cutting output by 6 dB per octave); second order (12 dB per octave); third order (18 dB per octave); and fourth order (24 dB per octave). The steeper the slope the quicker the attenuation.
dBm - dB referenced to 1 milliwatt. To convert into an equivalent voltage level, the impedance must be specified. For example, 0 dBm into 600 ohms gives an equivalent voltage level of 0.775V, or 0 dBu; however, 0 dBm into 50 ohms, for instance yields an equivalent voltage of 0.24 V. Since modern audio engineering is concerned with voltage levels, as opposed to power levels in the early years of telephone, the convention of using a reference level of 0 dBm is academic. But in the A/V industry, many people still refer to 0.775Vrms (600 r) as 0 dBm, which should be more accurately called 0dBu. In fiber optics, dBm is dB referenced to 1 mW of optical power.
dBSPL - dB referenced 20 micro pascals (0.00002 PA). 0dBSPL is a scale used to express acoustic energy, that is as loud as sound is. For example, when a sound is described as being “110 dB,” the measurement is expressing the sound pressure level of the source. Benchmarks include: 30-40 dBSPL - ambient room noise; 50-70 dBSPL -normal conversation; 110-120 dBSPL - rock concert; 130-140 dBSPL - painful sound.
dBu - dB unterminated. 0 dBu is a voltage reference point equal to 0.775Vrms. [This reference originally was labeled dBv (lower case) but was too often confused with dBV (upper case), so it was changed to dBu (for unterminated).] +4 dBu is a standard pro audio voltage reference level equal to 1.23Vrms. XLR and captive screw audio connectors are commonly used in this equipment.
dBV - dB referenced to 1.0 Vrms. -10dBV is a standard audio line level for consumer and some professional audio use, equal to 0.316 Vrms. RCA audio connectors are a good indicator of units operating at -10 dBV levels.
DC - Direct Current. The flow of electrons in one direction.
DC coupled - A circuit that passes both AC and DC components of a signal, and therefore is sensitive to DC offsets. Also see “AC Coupled.”
DC offset - Refers to the degree to which a DC voltage is skewed away from a zero or baseline value.
DC restoration - The correct blanking level for a video signal is zero volts. When a video signal is AC-coupled between stages, it loses its DC reference. A DC restoration circuit clamps the blanking at a fixed level. If set properly, this level is zero volts.
DCF - Dispersion Compensating Fiber
DDC - Display Data Channel. A bi-directional communications standard developed by VESA (Video Electronics Standards Association) that defines a universal data transmission standard for the connectivity between display devices and computers.
DDSP™ - Digital Display Sync Processing™. A signal handling method, trademarked by Extron, that allows the sync signal to pass through without altering sync pulse timing or width. DDSP disables other sync processing features such as horizontal and vertical centering.
DDWG - Digital Display Working Group. The DDWG develops standards for digital displays. Developer of the DVI standard.
Dead Zone - A region within a fiber optic system where an OTDR – Optical Time Domain Reflectometer cannot effectively make measurements.
Decoder - (1) A device used to separate the RGBS (red, green, blue and sync) signals from a composite video signal. Also known as an NTSC decoder. (2) The device in a synchronizer or programmer which reads the encoded signal and turns it into a form of control.
Deep Color - A very wide color gamut with a bit depth of 30 bits, capable of displaying billions of colors. The HDMI Licensing group has adopted Deep Color modes for the HDMI 1.3 specification. Deep Color is often stated as xvYCC color space.
Default gateway - The routing device used to forward all traffic that is not addressed to a station within the local subnet.
Definition - The fidelity with which a video picture is reproduced. The clearer the picture, the higher the definition. Definition is influenced by resolution.
Degausser - A device that produces a strong alternating electromagnetic field which quickly erases an entire reel, cassette, or cartridge of tape. Also used for eliminating ghosting in television monitors by demagnetizing the CRT.
De-interlacing - The process of combining pairs of interlaced fields of video into one progressive frame of video.
Delay - A basic DSP process in which the output of the input signal is delayed by a specified time
(called the delay time).
Dense Wavelength Division Multiplexing – DWDM - The multiplexing, or combining of several wavelengths into a single optical signal. DWDM is distinguished from Coarse Wavelength Division Multiplexing–CWDM in that the separation between wavelengths – 0.8 to 1.6 nm – is much smaller.
Detail - An adjustment that enhances/improves image sharpness.
Detector - A device within fiber optic receivers that converts optical energy to electrical energy.
DHCP - Dynamic Host Configuration Protocol. A standardized client-server IP networking protocol that enables network administrators to centrally and automatically manage the assignment of IP addresses in an organization’s network.
Dichroic - A type of mirror, reflector, or filter that selectively reflects different wavelengths of light, permitting a projector to transmit more visible light with less heating of the film. Dichroic mirrors are also used for internal convergence of three-tube single lens video or computer projectors.
Dielectric - Insulating material in coaxial cables between center conductor and outer conductor.
Differential audio - See “Balanced audio.”
Differential gain - Unwanted variations in a chrominance subcarrier’s amplitude that result from changes in the
signal’s DC level, usually specified between 10% and 90% of full scale .
Differential Mode Delay – DMD - A limiting factor in the performance of transmissions over multimode fiber, in which there is a differential in the arrival times at the receiver of various wavelengths, or modes along the fiber. This differential is caused by model dispersion which is inherent in multimode fiber.
Differential phase - Unwanted variations in a subcarrier’s phase as a result of changes in the chrominance signal’s DC level, usually specified in degrees over a frequency range.
Digital - A system of data or image values in the form of discrete, non-continuous codes, such as binary. When data is in a digital format, it can be processed, stored (recorded), and reproduced easily while maintaining its original integrity.
Digital Betacam® - A component digital videotape recording format that conforms to CCIR 601 standard, using 1/2” tape, 10 bits, 2:1 compressed. The primary manufacturer is Sony.
Digital component video - See “Component Digital.”
Digital composite video - “See Composite Digital.”
Digital control - A method using discrete digital impulses to control individual functions within a system.
Digital signal - An electrical signal which possesses two distinct states (on/off, positive/negative); typically represented by “0” or “1”.
Digitization - The transformation of an analog signal into digital information.
Digitizers - Video digitizers utilize video cameras to take pictures of photographs or live and still action. The information is decoded into RGB (digital form) and stored in the frame buffer.
D-ILA™ - Direct Drive Image Light Amplifier. The D-ILA is a device based on the Image Light Amplifier or ILA developed by Hughes-JVC Technology Corporation. The D-ILA technology is a reflective liquid crystal modulator whereby electronic signals are addressed directly to the device. The D-ILA device has an X-Y matrix of pixels configured on a C-MOS single crystal silicon substrate mounted behind the liquid crystal layer using a planar process that is standard in Integrated Circuit technology.
DIN connector - An acronym for Deutsche Industrie Norm. A round connector with notches, or keys, for alignment. They exist in several sizes: 4 pins, 5 pins, 8 pins, etc. A convenient way of combining all of the signal lines in one connector, 4-pin DIN connectors are often used for S-video.
Diode - An electronic device that allows current to flow in one direction only.
DIP - Dual In-line Package. A universal method of manufacturing integrated circuits (ICs) with the pins arranged in two parallel rows. Some DIP components are soldered in and some use DIP sockets.
DIP switches - Small switches that are used to change settings on printers, computers, interfaces, switchers, modems, etc. They are designed to fit in a DIP (Dual Inline Package) space on a circuit board.
Dispersion - A limiting factor in optical fiber transmission performance, where a light pulse is broadened, or separated into modes or individual wavelengths. Dispersion limits transmission bandwidth and distance capability. The two major types of dispersion are modal dispersion and chromatic dispersion.
Dispersion Compensating Fiber – DCF - A special type of fiber designed to exhibit a large negative dispersion. DCF is typically used in long-haul telecommunication systems to compensate for dispersion in optical fiber.
Dispersion Shifted Fiber – DSF - A single-mode optical fiber with its optimal dispersion wavelength shifted, through the addition of dopants, to a wavelength that delivers optimal attenuation.
Display device - Any output device for presenting information visually. Examples include: CRT (Cathode Ray Tube), LED (Light Emitting Diode), or LCD panel (Liquid Crystal Display). A general term for a projector or monitor.
DisplayID - Released in December 2007, this second-generation version of VESA EDID -Extended Display Identification Data I sintended to replace all previous versions. DisplayID represents a 256-byte data structure that conveys display-related information to attached source devices. It is meant to encompass PC display devices, consumer televisions, and embedded displays such as LCD screens within a laptop without need for multiple extension blocks. DisplayID is not directly backward compatible with previous EDID/E-EDID versions.
DisplayPort - The newest digital audio/video interconnect standard, designed primarily for use between a computer and display device. DisplayPort supports data rates up to 8.64 Gbps at a distance of 2m over standard copper cable. DisplayPort is not directly compatible with DVI or HDMI, but a DisplayPort connector can pass these signals, and the standard does provide an emulation mode for ease of integration with DVI or HDMI equipped products.
Dissolve - (1) An effect in which one scene or picture fades out as another fades in. In projection, the dissolve effect is achieved by varying the intensity of the lamps in the two projectors involved. Sometimes called lap dissolve or cross fade. (2) The hardware controlling the dissolve effect, which is properly called dissolve control or dissolve unit. A visual effect wherein one scene gradually fades away while slowly being replaced by another. See “Fade, Fade-to-black.”
Distribution amplifier - A device that distributes multiple outputs from a single source input. Distribution Amplifiers (DAs) split signals, but also provide amplification and enhancement features to maintain the integrity of the signals.
Distribution Cable - Fiber optic cable comprising a bundle of jacketed fibers encased within an outside jacket.
Distribution Panel - For fiber optic applications, this is both a patch panel and splice panel, usually installed at a hub or entrance facility
Dither - (1) The process of filling a gap between two pixels with another pixel having an average value of the two to minimize the difference or add detail to smooth the result. (2) In audio, a process that deliberately adds a tiny amount of noise to a signal in order to mask unwanted sounds introduced when the signal’s original bit depth is reduced. Dithering is recommended when transferring audio to a device that uses a lower bit depth.
DLP™ - Digital Light Processing. An imaging technology for video projection developed by Texas Instruments, based on the modulation of light reflected from mirror elements known as Micromirrors(tm). Each pixel is represented by its own Micromirror, which mechanically tilts in accordance to the extent of light reflected toward or away from the screen. A matrix of Micromirrors comprising the video image is situated on a microchip, or DMD(tm) (Digital Micromirror Device). DLP is implemented as a three-chip configuration (one DMD for each of the RGB colors), or as a one-chip configuration (R, G, and B are sequentially processed by a single DMD via a color wheel).
DMI™ - Dynamic Motion Interpolation™. This Extron video processing technique is an advanced motion prediction and compensation method that treats motion content and still content with different algorithms to yield high fidelity images.
DMM - Digital Multimeter. A test and measurement device, typically handheld, that combines measurement tools for voltage, amperage, resistance, and other common electrical and electronic measurement needs.
DNS - Domain Name System. DNS is the way that an Internet domain name is located and translated into Internet Protocol (IP) addresses. A domain name is a meaningful and easy-to-remember “handle” for an Internet address.
DOC - Declaration of Conformity. A document that states the European Union directives and standards to which particular equipment should comply.
Dolby noise reduction - A patented noise reduction technique from Dolby Labs that raises the volume of sound track elements most likely to be affected by inherent noise during recording and then lowers them again during playback so that the noise seems lower in relation to the wanted elements of the audio recording.
Dolby® Digital - A digital audio encoding and decoding technology utilized for DVDs, Blu-ray Discs, and many cable and satellite television services. Dolby Digital can transmit mono or standard two-channel stereo audio, as well as 5.1 channel surround sound (left front, center front, right front, left rear, right rear, and sub-woofer).
Dolby® Digital Plus (Dolby Digital plus 2 additional channels, optional format for Blu-ray) - A digital audio compression technology designed as an optional codec for use with Bluray Disc. Digital Plus is an extension of the earlier Dolby Digital format and supports up to 13 audio channels, although Blu-ray Disc is limited to 8 discrete channels. The extra audio channels are often used to support multiple languages.
Dolby® TrueHD - An advanced, lossless multi-channel audio encoder and decoder technology intended primarily for high-definition content and is optional for Blu-ray Disc; support for TrueHD is also optional in the HDMI 1.3 specification. TrueHD supports up to 8 discrete audio channels at 96 kHz sampling, or up to 6 channels at 192 kHz sampling. Since TrueHD is optional for Blu-ray Disc, discs encoded with a TrueHD audio track must also include a separate 2-channel digital audio track.
Domain - When referring to the Internet, a name that identifies a network. (i.e. yahoo.com)
Dot clock - Also referred to as pixel clock. The timing device in a graphics card that determines the pixel resolution. The dot clock runs at a rate that produces the highest possible pixel resolution for that device. In a digital projector, the dot clock samples the analog video at a rate that produces the resultant pixel resolution. See “Pixel clock.”
Dot crawl - Sometimes called “zipper effect,” dot crawl refers to a specific image artifact that is a result of the composite video system. Dot crawl may be seen on TV news, for example, when a picture appears over the anchorperson’s shoulder, or when some text appears on top of the video clip. If you look closely, along the edges of the picture, or the text that has been overlaid, you’ll notice some jaggies rolling up or down.
Dot pitch - The vertical distance (measured in millimeters) between the centers of like-colored phosphors that are in adjacent pixels on the monitor screen. The closer the spacing, the better the resolution. Dot pitch is specified in pixels/mm.
DPCP - DisplayPort Content Protection - DPCP is a content-protection scheme for DisplayPort, developed by Advanced Micro Devices. Like HDCP 2.0, DPCP uses AES 128 encryption.
Drain wire - Non-insulated wire used in cable termination as a ground connection.
DRM – Digital Rights Management - A generic term for technologies such as content scrambling in cable or satellite television transmission, HDCP, and DPCP that can be used to control the access to, or reproduction of, copyrighted, commercially-available content. DRM is used primarily to prevent piracy, the unauthorized duplication and distribution of copyrighted material. However, DRM often also governs how content can be used. Commercially-available DVDs and Blu-ray Discs, for example, are typically licensed for personal use in a residential environment. Use of such content in a public venue, such as a school or business setting, without express consent or licensing by the copyright holder, is typically in violation of the media’s license.
Dry contact closure - A pair of electrical contacts that carry no live voltage.
DSP - Digital Signal Processor. A specialized CPU or circuit designed to process signals such as audio and video which have been converted to digital form. DSP is used to process sound, video, and images in a variety of ways.
DSS - Digital Satellite System.
DSVP™ - Digital Sync Validation Processing™. In critical environments or unmanned, remote locations, it is vital to know that sources are active and switching. Extron’s exclusive DSVP technology confirms that input sources are active by scanning all sync inputs for active signals. DSVP provides instantaneous frequency feedback for composite sync or separate horizontal and vertical sync signals via the switcher’s RS-232/422 port.
DTS Digital Surround - A digital audio encoding and decoding technology from DTS, Inc. that delivers 5.1 channels of surround sound. It is an optional surround sound format for DVDs but is mandatory for Blu-ray Disc. DTS Digital Surround has also been used in some LaserDisc releases as well as CDs, and is also featured in some video games.
DTS-HD High Resolution Audio - A multi-channel digital surround sound audio format used in commercial and consumer applications. DTS-HD High Resolution audio was one of the earliest multichannel formats, first used theatrically with the release of Jurassic Park in 1993. It is also commonly used in DVD and some CD audio releases, as well as several late Laserdisc format releases.
DTS-HD - High Resolution Audio is optional for Blu-ray Disc and is not part of the HDMI specification.
DTS-HD Master Audio - A lossless audio encoder/decoder technology developed by Digital Theater System. DTS-HD Master Audio allows a bit-for-bit representation of the original movie’s studio master soundtrack and supports up to 8 audio channels. Support for DTS-HD Master Audio is optional in the HDMI1.3 specification released in 2006.
DTV - Digital Television. Often used to describe one of the many new forms of digital terrestrial transmission of video program material.
Dual Link - Dual Link DVI supports 2 x 165 MHz (2048 x 1536 at 60 Hz, 1920 x 1080 at 85 Hz). A dual link implementation utilizes all 24 of the available pins.
Dual-Link DVI - Dual Link DVI supports 2 x 165 MHz (2048 x 1536 at 60 Hz, 1920 x 1080 at 85 Hz). A dual link implementation utilizes all 24 of the available pins. A dual-link DVI output has two TMDS links and twice the bandwidth of single-link DVI, and can therefore support much higher resolutions. With two TMDS links, the number of data channels is doubled, although there is still only one clock signal, so both links are clocked identically. Apple’s 30” Cinema Display with a native resolution of 2560x1600, is an example of a display requiring dual-link DVI. See also “Single-Link DVI.”
Dual-Link HD-SDI - See “SMPTE 372M.”
Duplex - Data transmission in both directions. Half duplex denotes transmission in one direction at a time, while full duplex refers to simultaneous transmission in both directions. In fiber optics, duplex also refers to a type of cable comprising two fibers for duplex transmission.
Dust Cap - A plastic cap that covers the connector ferrule, plug, or sleeve, and protects the connector endface.
DV - Digital Video. A serial digital video format. DV has the advantage over standard analog video of maintaining clear, crisp video without degradation from generation to generation.
DVB/ASI – Digital Video Broadcasting/Asynchronous Serial Interface - A standard for the broadcast of digital television signals. Terrestrial broadcast, primarily seen in Europe, is often stated as DVB-T. In the US, DVB-S is often used for compression and encoding of digital satellite transmission; for terrestrial applications, North America utilizes the ATSC standard.
DVD - Digital Versatile Disc. An optical disc similar in physical size to a CD-ROM, but capable of storing an entire movie. The technology uses MPEG-2 compression. Typical capacity for these discs is 4.5 GB, or about 133 minutes of digital video.
DVD-Audio - A digital format for delivering high-fidelity audio content on DVD – Digital Versatile Discs. DVD-Audio is a standalone format intended for audio only and is not used for the audio portion of DVD video content. DVD-Audio is similar in application to SACD, although to maintain compatibility with DVD players, the format is not capable of the very high sampling rates found in SACD. Support for DVD-Audio was added to the HDMI 1.1 specification in 2004.
D-VHS - Digital-VHS. A new technology based on VHS, offering the features of conventional VHS with bit stream recording capability which allows the recording and playback of compressed digital data including digital television broadcasts and prerecorded high definition software.
DVI - Digital Visual Interface. The digital video connectivity standard that was developed by DDWG (Digital Display Work Group). This connection standard offers two different connectors: one with 24 pins that handles digital video signals only, and one with 29 pins that handles both digital and analog video. This standard uses TDMS (Transition Minimized Differential Signal) from Silicon Image and DDC (Display Data Channel) from VESA (Video Electronics Standards Association).
DVI-D - DVI connector that supports digital signals only.
DVI-I - DVI connector that supports both digital and analog signals.
Dynamic IP address - An IP address that is automatically assigned to a client host in a TCP/IP network, typically by a DHCP server. Network devices that serve multiple users, such as servers and printers, are usually assigned static (unchanging) IP addresses.
Dynamic range - The highest and lowest potential signal levels on a given device. Also applies to fiber optic applications in terms of the ratio between the most – or strongest – and least – or weakest – observable optical signals.
Dynamic transducer - Technical description of a loudspeaker or dynamic microphone. A dynamic transducer uses a paper, plastic, fabric, or metal cone which is driven by a voice coil that moves back and forth through a magnetic field produced by the audio signal.
Echo cancellation - A DSP technique that filters unwanted signals caused by echoes from the main audio source.
Echo suppression - Used in telephone networks to reduce the impact of echo and thereby improve voice quality. The impact of echo suppression is usually to limit data transmission to one direction at a time. In order to provide for duplex operation, modems request telephone systems to turn off echo suppression.
ECL - Emitter Coupled Logic. A family of high speed, low power IC logic devices. Also called “current mode logic.”
Edge-to-edge - Describes common density factors in loudspeaker layout designs. Edge-to-edge density places the speakers such that the outside edges of their sound cones just touch one another.
EDID - Extended Display Identification Data - EDID is a data structure used to communicate video display information, including native resolution and vertical interval refresh rate requirements, to a source device. The source device will then output the optimal video format for the display based on the provided EDID data, ensuring proper video image quality.
EDID Minder - A proprietary EDID management process from Extron. EDID Minder automatically manages the EDID information between a digital display device and one or more input sources. By maintaining continuous EDID communication with all sources, EDID Minder ensures that digital sources power up properly and maintain their video output, whether or not they are actively connected to the digital display device.
EDTV - Enhanced Definition Television. A new digital TV product category added between High Definition TV (HDTV) and Standard Definition TV (SDTV), with the following attributes: a receiver that accepts ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats; a display scanning format with active vertical scanning lines of 480 progressive (480p) or higher; no aspect ratio specified; and receives and reproduces, and/or outputs Dolby Digital audio.
EEPROM - Electrically Erasable Programmable Read-Only Memory. The information in an EEPROM is erased by exposing it to an electrical charge. Similar to EPROM except in the way in which information is erased. See “Flash memory.”
Effective modal bandwidth - In fiber optics, the modal bandwidth of a multimode fiber when using a laser as a light source.
EGA - Enhanced Graphics Adapter. Introduced by IBM in 1984, this replaced CGA (Color Graphics Adapter).
EIA - Electronics Industries Association. The association that determines recommended audio and video standards in the US.
EIA sync - The standard broadcast sync, also called EIA-RS-170.
EIA-RS-170 - The standard broadcast sync as determined by the Electronics Industries Association. Commonly called EIA sync.
Electrode - In a fusion splicer, the component which discharges electricity to enable two optical fibers to be fused or welded together.
Electron gun - The part in the CRT that produces the electron beam attracted to the phosphor-coated back surface of the screen. The beam strikes the phosphors, causing them to emit red, green, or blue light, creating images on the screen.
Electrostatic focus - Also referred to as electrostatic deflection. A CRT tube focusing method that uses electrically charged plates instead of deflection coils to focus the electron beam. This method was used only on small CRTs because the larger the CRT, the higher the voltage required, which can cause harmful x-rays to be emitted.
ELFEXT - Equal Level Far End Crosstalk. The amount of crosstalk at the far end after compensation for attenuation over a run.
Embedded data - Digital technologies such as SDI, HD-SDI, and HDMI, can carry variety of other data along with the primary video data, including audio, control, metadata such as content title or other identifying information, or other ancillary information. These data are said to be embedded, as they travel with the primary signal from the source device to the destination.
EMI - Electromagnetic Interference. Any electromagnetic disturbance that interrupts, obstructs, or otherwise degrades or limits the effective performance of electronics/electrical equipment.
Encoder - A device, often built into video cameras, that changes individual component signals into composite signals. For example, an encoder combines Y (luma) and C (chroma) signals to produce a video image.
Encoding - In video, the combination of electronic elements into one signal; for example, S-video is encoded (combined) to create a composite video signal.
Encryption - To manipulate information into a coded form that cannot be read without a device that will unscramble the code. Video signals are also scrambled in cable and pay-TV systems so that the viewer must pay to receive the program after it has been electronically deciphered.
End Finish - The endface of an optical fiber at the ferrule, finished or polished to be smooth in order to minimize signal loss or backreflection. PC, SPC, UPC, and APC polishing finishes are available for single-mode connectors.
Entrance Facility - In fiber optic applications, the entrance to a building for fiber optic cables.
Epoxy - An adhesive that bonds between surfaces by means of a chemical reaction in which the adhesive cures as it dries. Epoxy is used in fiber optic applications to adhere a connector ferrule to the fiber.
EPROM - Erasable Programmable Read Only Memory. A device that can store information (instructions or data) and retain it when power is removed. An EPROM is erased by exposing it to ultraviolet light. New information is loaded into the EPROM using a PROM programmer or “burner.” See “Flash memory.”
EQ (Audio) - Equalizer. An audio signal processor used to add or attenuate frequencies in order to change the character of the resulting sound. EQ’s are properly used with a reference signal (see pink noise) and a real- time analyzer to ensure that the sound from the speakers closely matches the original sound.
EQ (Video) - Equalization. Selective amplification or signal restoration applied to a signal to compensate for high frequency attenuation and other distortions encountered in long lengths of cable.
Equalizing pulses - These pulses cause the vertical deflection to start at the same time in each interval. They also keep the horizontal sweep circuits in step during the portions of the vertical blanking interval immediately preceding and following the vertical sync pulse.
Error detection and correction - The ability to detect errors caused by interference or other factors during the transmission of a signal, and then reconstruct the received signal so that it is a faithful reproduction of the original signal, without errors. A process known as Forward Error Correction is often used to allow the receiver to detect and correct some errors without having to “ask” the transmitter to send additional data.
Ethernet - A network protocol that uses MAC addresses to exchange data between computers. Using ARP, with TCP/IP support, Ethernet devices can be connected to the Internet. An Ethernet LAN typically uses unshielded twisted pair (UTP) wires. Today’s Ethernet systems provide transmission speeds of 10 Mbps or 100 Mbps. Ethernet is mostly based on the IEEE 802.3 standard.
Expansion slots - Slots inside a cabinet that are used to connect additional circuit modules (cards).
Extrinsic Joint Loss - The portion of optical signal loss at a joint that is not intrinsic to the optical fibers, usually caused by misalignment between the fibers, end separation, and imperfections in the end finish of either fiber.
Eye Pattern - The representation of a digital signal on an oscilloscope in which a digital data signal is repetitively sampled. Distortion in the signal waveform due to interference and noise appears as closure of the eye pattern. Signals that are poorly synchronized with the system clock (also known as jitter), too high, too low, too noisy, too slow to change, or which have too much undershoot or overshoot, can be observed from the eye pattern.. Eye patterns are used to evaluate the quality of digital signals when passed through cables or signal extension devices, switchers, signal processors, and other electronics.
F connector - A type of plug used for RF video connections, such as those used to connect TV antennas and cable TV to televisions and VCRs.
Fabry-Perot – FP - A standard laser diode that uses a laser oscillator comprised of two mirrors with an amplifying medium between them.
Fade, Fade-to-black - A gradual dissolve to another picture, often an all black screen.
Fan-Out Kit - In fiber optics, a kit designed for use with loose tube cable with bare fiber bundles in each buffer tube. The kit enables termination as well as protection of these bare fibers.
Far end - In videoconferencing, the party or group you are connecting to at the distant site.
Farad - Unit of measurement for capacitance which stores one coulomb of electrical charge when one volt is applied. More commonly, stated in picofarads, or one-millionth of one-millionth (10e-12) of a farad.
Fault - In fiber optics, any part of an optical fiber that deviates from normal performance.
Fault Finder - A simplified optical time domain reflectometer – OTDR, an instrument used to detect breaks within a run of optical fiber. Also known as a Fiber Break Locator.
FCC - Federal Communications Commission. The US governmental agency that controls and makes all policy for the use of broadcast airwaves.
FED - Field Emissive Display. FED technology is similar in operation to CRTs in that phosphor is excited by a stream of electrons traveling through a vacuum. “Emissive” refers to the light-emitting characteristic of the display; unlike LCD flat panel displays, a backlight is not required for image display. Because FEDs are emissive, they allow equal brightness at all viewing angles.
Feedback - (also known as Larson effect) The phenomenon where the sound from a loudspeaker is picked up by the microphone feeding it, and then reamplified again and again. The resulting loop between audio input (the microphone) and audio output (the loudspeaker) results in a scream or squeal emitted from the loudspeaker. Feedback is determined by the resonant frequencies in the amplifier and loudspeakers, the acoustics of the room, the design of the microphone, and the relative positions of the microphone and loudspeaker.
FEP - Fluoro Ethylene Polymer. Teflon FEP is used as a Foaming Dielectric for all of our Plenum Rated Coax Products
Ferrule - A precision tube which centers an optical fiber and provides stabilization and precise alignment. A ferrule may be part of a connector or a mechanical splice.
Ferrule Connector - FC - A screw-type optical fiber connector that features a keying mechanism. FCs are typically designated as FC/PC, FC/SPC, or FC/APC to denote physical contact, super physical contact, or angled physical contact, respectively.
FFT - Fast Fourier Transform. Converts analog waveforms into a form that can be easily analyzed for DSP applications.
Fiber - The basic optical transmission element. The components of a fiber include the core, surrounded by the cladding, and then a coating for protection. Specific optical properties of the core and cladding enable light to be contained within the core as it travels along the fiber.
Fiber Break Locator - An instrument used as simplified method of locating breaks within an optical fiber. Also known as a Fault Finder.
Fiber Coating - A coating surrounding the cladding of an optical fiber during the draw process to protect the fiber from handling and the environment.
Fiber Distribution Unit – FDU - An enclosure that houses and organizes groups of optical fibers.
Fiber Optic Cable - A telecommunications cable comprising one or more optical fibers.
Fiber Optics - The transmission of light through optical fibers for telecommunications applications.
Fiber Surface Finish - A term describing or denoting the quality of the polishing at the end of a fiber. Fiber to the Building/Business – FTTB Fiber optic service to a business or building.
Fiber to the Curb – FTTC - Fiber optic service to a node within a residential neighborhood. The node in turn feeds several homes via copper wiring.
Fiber to the Desk – FTTD - Fiber optic runs to individual desktops.
Fiber to the Home – FTTH - Fiber optic service to individual homes.
Fibre Channel - An industry standard for connecting computers for gigabit-speed transmission over twisted pair and optical fiber at distances up to 10 km.
Field - A field is one half of a standard television frame, containing every other line of information. Each standard video frame contains two interlaced fields, sometimes referred to as field 1 and field 2. In the NTSC video system, a field contains 262.5 lines and a frame contains 525 lines. In the PAL video system, a field contains 312.5 lines and a frame contains 625 lines.
Figure 8 - In fiber optics, a method of polishing the end of a connector in a figure 8 pattern to minimize scratches.
File - In computers, a record of related information that may be stored in memory, on a disk, or other media. Files can contain text, graphics, data, or programs.
Fillers - Non-conducting materials incorporated into the construction of a fiber optic cable to add roundness, flexibility, tensile strength, or a combination of all three.
Filter - In general, a filter accepts the desired and rejects the undesired. Every filter has a specific purpose. In electronics, for example, if you have some high frequency noise mixed with the signal that you want, then a lowpass filter is used to pass the signal and reject the (high frequency) noise. In software, a filter allows the application to open a file of a specific format.
Firewall - A device that isolates and protects a network from outside intrusion.
FireWire™ - A trademark of Apple. Also known as 1394 or IEEE-1394. A data communication standard used primarily with digital camcorders, 1394 FireWire manages the data transfer and tape transport control processes when transferring DV (digital video) to your computer or DV editing system. FireWire supports data transfer rates of 100 to 400 Mbps.
First surface mirror - The front of a mirror. In mirrors intended for A/V applications, the first surface is coated with a reflective material to prevent double images (ghosting).
FL - Focal Length. The distance between the center of a lens and the point where the image comes into focus. In projection, a shorter focal length yields a larger image on the screen for any given projection distance.
Flash memory - A special version of an EEPROM that can be rewritten while in its functioning environment, instead of having to be removed and reprogrammed in a special device. Example: memory for a digital camera.
Flat (response) - A theoretical ideal for audio components, especially speakers, that represents a frequency response that does not deviate from a flat line over the audible frequency spectrum. A flat response, though ideal, is impossible in real world listening due to the speaker itself and its interactions with the room and various surfaces within the room. All speakers will fluctuate above and below the ideal flat response, but speakers that stay within two or three dB of a flat response are considered very linear and very nearly flat in their response.
Flat field - A solid field of color used to calibrate monitors and projectors. A full white flat field is typically used to evaluate the uniformity of a projected image.
Flat polish - In fiber optics, a condition at a ferrule where the endfaces of a fiber optic cable and the ferrule tip are polished flat.
Fletcher-Munson effect - Also referred to as “equal loudness contours.” Fletcher and Munson, researchers at Bell Labs, first measured the sensitivity of human hearing at various volumes and frequencies. Fletcher and Munson found that human hearing is dependent on loudness, and that the ear is most sensitive in the range of 3 kHz to 4 kHz. Sensitivity falls off rapidly at lower frequencies and somewhat more slowly at higher frequencies. Sounds in frequencies below and above this range need to be louder (more powerful) in order to be heard clearly. The loudness control found on audio reproduction systems is designed to compensate for the Fletcher-Munson effect.
Flicker - An alternating change of light intensity, typically perceived at a rate of a few Hertz to 60 Hz when viewing static images such as text. Flicker can occur when the electron gun paints the screen too slowly, giving the phosphors on the screen time to fade before being refreshed. This may occur when the refresh rate of the video is too low, or when the persistence of the display device is too short. A fluorescent light fixture may produce the same effect.
Fluorocopolymer - Describes Teflon FEP in Generic Term.
Flutter - Pitch variations heard as a fast wavering or wobbling caused by an audiotape or CD moving at varying speeds. See “Wow.”
FM - Frequency Modulation. A method of combining an information signal with a carrier signal so that it may be transmitted. FM radio is frequency modulated. Audio is encoded on the carrier by varying the frequency in response to the audio.
Focus - To adjust a lens to make the image appear sharp and well defined. The best possible resolution of an image, showing the image to be sharp and well defined.
Focus coil - Deflection coil. An electromagnetic coil that surrounds a video tube and bends the electron beam onto a screen.
Foot candle - A unit of illumination from one candle at a distance of one foot. Equal to one lumen incident to one square foot.
Foot lambert - See “Luminance.”
FOTS - Fiber Optic Transmission System.
FPC - Front Panel Controller, Extron’s term for the front panel control system used with larger matrix switchers such as the Matrix 3200/6400 and Matrix 12800 series models. The FPC provides simple, touch-of-a-button control of the matrix switcher and eliminates the need for a computer or third party control system to operate the matrix switcher.
FPS - frames per second. A measure of information that is used to store and display motion video. Each frame represents a still image and displaying frames in succession creates the illusion of motion. The more frames per second (fps), the smoother the motion appears.
Frame - In interlaced video, a frame is one complete picture. A video frame is made up of two fields, or two sets of interlaced lines. In film, a frame is one still picture of a series that makes up a motion picture.
Frame synchronizer - Stores each incoming frame of video and releases it as the next frame comes in. Frame synchronizers convert analog video to digital and are typically used to synchronize two or more sources.
Frequency - The number of times a particular event happens per a given time. In A/V, the number of complete cycles per second of a musical tone or electronic signal, expressed in Hertz (Hz).
Frequency Division Multiplexing – FDM - The combining of two or more signals into a single carrier signal for transmission through FM – frequency modulation. Each signal modulates the carrier signal at a different region of the frequency spectrum.
Frequency domain - The means of representing a signal as a plot of amplitude (normally on the vertical axis) versus frequency (normally on the horizontal axis). A spectrum analyzer represents signals in the frequency domain. See “Time Domain.”
Frequency range (audio) - The range of frequencies between high and low end points; for example, in audio, the frequency range of the human ear is said to be 20 Hz to 20,000 Hz. Individual speaker elements like woofers, midranges and tweeters serve different frequency ranges within the overall audio frequency range.
Frequency range (video) - Refers to the low-to-high limits of a device, such as a computer, projector, or monitor. Also see “Bandwidth.”
Frequency response - The frequency range over which signals are reproduced within a stated amplitude range. Generally expressed in Hz vs. dB. For example: 100 - 5000 Hz +/- 3dB means that the device can handle a frequency range of 100 to 5000 Hz with a possible deviation in amplitude within that frequency range of +3 to -3dB.
Fresnel lens - A thin, flat lens made by cutting concentric circular grooves into its surface. The grooves act like prisms to bend and focus light. The Fresnel lens is often used for the condenser lens in overhead projectors and in studio spotlights.
Fresnel reflection - The partial reflection of light that occurs at the boundary between two materials with different indexes of refraction. In fiber optics, this is considered a loss when light is partially reflected at a glass-air interface.
Front porch - The black or blanking portion of the composite picture signal lying between the leading edge of the horizontal blanking pulse and the leading edge of the corresponding horizontal sync pulse. See “Blanking.”
Front projection screen - A light-reflecting screen used when the image is projected from a source in front of the screen. Also see “Rear projection screen.”
Front screen projection - To project an image from the audience’s side of a light-reflecting screen.
FTP - File Transfer Protocol. A protocol used to transfer files over a TCP/IP network (Internet, UNIX, etc.). For example, after developing the HTML pages for a Web site on a local machine, they are typically uploaded to the Web server using FTP.
Full duplex - The ability of a device or line to transmit data simultaneously in both directions.
Full Duplex Operation - When data is being both sent and received simultaneously. (i.e., sound cards, network interface cards, hubs)
Fully loaded - Refers to the condition when all inputs (in the case of a switcher) or all outputs (in the case of a distribution amplifier) or both (in the case of matrix switchers) are connected to loads/devices, that is, the product has a maximum load connected. This is pertinent because if a product is not properly designed, the voltage and the bandwidth can decrease and the signal can drop out as more and more loads are connected, or crosstalk can be a greater problem as more signals appear on the inputs or outputs.
Function keys - Keys that are programmed to perform specific tasks, such as macro-operations.
Fundamental rejection - Usually expressed in dB, the amount by which a total harmonic distortion (THD+N) analyzer rejects the fundamental component of the input signal. The lowest measurable distortion of THD+N analyzer is limited by the fundamental rejection, along with several other attributes. See “THD” and “THD+N.”
Fusion splicer - An instrument that is used to bond, or fuse two optical fibers together by heating, usually generated by a high intensity electrical arc.
Gain - (1) A general term for an increase in signal power or voltage produced by an amplifier. The amount of gain is usually expressed in decibels above a reference level. Opposite of attenuation. (2) The amplification of a signal, unit, or system. Expressed in the unit of measurement appropriate to the signal or system. (3) In fiber optics applications, the measurement of back reflections using an OTDR - Optical Time Domain Reflectometer, due to a mismatch in core sizes between adjoining optical fibers.
Gainer - In fiber optics applications, a backscatter measurement condition with an OTDR that indicates a splice loss, due to a mismatch in core size between the two optical fibers. The resulting trace indicates a perceived increase in power, and is therefore known as a “gainer.”
Gamma - The light output of a CRT is not linear with respect to the voltage input. The difference between what you should have and what is actually output is known as gamma.
Gamma correction - Before being displayed, the linear RGB data must be processed (gamma corrected) to compensate for the gamma of the display.
Gang - Refers to the number of wiring devices that can be installed in an electrical box, (e.g., “two gang” refers to a box that can accommodate two duplex receptacles, “three gang” refers to a box that can accommodate three duplex receptacles, etc).
Gateway - A device that interconnects networks with different, incompatible communication protocols.
Genlock - A method of synchronizing video equipment by using a common, external signal. This locks the sync generators of multiple devices to a single source.
Ghost - Also called “ghosting,” or “reflections.” A shadowy or weak duplication of the original image. It can be the result of transmission conditions where secondary signals are created and then displayed earlier or later than the original signal. Ghosts can also be the result of burning an image on a screen or by a mirror.
GHz - Gigahertz. One billion cycles per second.
Giga - The prefix abbreviation for billion. (G) One G-Byte = 1 billion bytes.
Global presets - The Extron matrix switcher output configuration settings that can affect all output connections/ties and can be saved/recalled by simply pressing a button or issuing a Simple Instruction Set (SIS™) command.
Graded index fiber - An optical fiber in which the index of refraction within the core of a multimode fiber decreases with the radius from the fiber axis. The index of refraction usually follows a parabolic profile from the fiber axis to the cladding, effectively addressing modal dispersion throughout the fiber link.
Graded Index Plastic Optical Fiber – GI-POF - A plastic multimode optical fiber with an index of refraction within the core that decreases from the fiber axis to the cladding. The index of refraction usually follows a parabolic profile from the fiber axis to the cladding, effectively addressing modal dispersion throughout the fiber link.
Graphic equalizer - An active electronic device which allows the adjustment of narrow ‘bands’ of audio frequencies to correct for recording and listening room deficiencies. Graphic equalizers generally have sliding levers, known as faders, representing the different ranges of frequencies between 20 and 20,000 Hz. (See EQ-Audio)
Ground - Electrical connection of a circuit to a point designated as having zero potential.
Ground loop - A potential system grounding problem that may produce symptoms that appear as sync noise and cause a horizontal bar (hum bar) to roll vertically on the video image. A ground loop occurs when some devices in a system are not connected to the same electrical ground as the other devices. This can create a voltage potential difference between ground on the pieces of equipment.
Group delay - The amount of delay or rate of phase shift with respect to frequency though a device or cable.
GVIF - Gigabit Video Interface. A transmission and connectivity standard developed by Sony that is used for digital video connections on the Sony VAIO desktop computer systems and Sony laptop PCs.
H - See “Horizontal sync.”
H.264 Encoding - A standard for video compression equivalent to MPEG-4 Part 10 or MPEG-4 AVC – advanced video coding. H.264 was created to provide video quality suitable for high definition applications at bit rates lower than that utilized in MPEG-2, the compression standard used in DVD authoring.
H.320 - ITU-T H.320 is a family of standards developed for video teleconferencing systems using ISDN. It references H.261 (for video); G.711, G.722, and G.728 (for audio); H.221, H.230, H.231, H.233, H.234, H.242, and H.243 (for control).
The standard allows a system from one manufacturer to talk to a system from another manufacturer, just as two different brands of FAX machines can talk to each other.
H.323 - ITU standard allowing audio, video, and data to be transmitted by way of the Internet Protocol (LAN/WAN). It is the umbrella standard defining multiple codes, call control, and channel setup specifications. Basically, videoconferencing over IP.
Half duplex - Data or audio transmission that can occur in two directions over a single line, but only one direction at a time.
Halogen-free (LSFOH) - Low Smoke and Fumes Zero Halogen. Refers to the material used in cable insulation that emits reduced amounts of hazardous smoke and toxic fumes in the event of a fire. Certain countries, such as in the UK, may require LSFOH cable insulation.
Handshake - In communications, the moment when the transmitting and receiving devices identify themselves to each other.
Harmonics (in music: overtones) - Multiples of an original frequency that add to and modify the original frequency. A pure sine wave is free of harmonics. When harmonics occur in electronic signals, it adds distortion to the original signal, causing undesirable results.
HD connector - A high-density D connector having its pins arranged close together, sometimes in three rows instead of two rows. Example: a 15-pin VGA connector (HD) vs. a Mac connector (D).
HDCP – High-bandwidth Digital Content Protection - A digital rights management scheme developed by Intel to prevent the copying of digital video and audio content. HDCP is mandatory for the HDMI interface, optional for DVI. HDCP defines three basic system components: source, sink, and repeater. Sources send content to the display. Sources can be set-top boxes, Blu-ray Disc players, computer-graphics cards, and so forth. A source can have only one HDMI/HDCP transmitter. Sinks decrypt the content so it can be viewed. Sink is typically used to describe a flat panel display, television, or projector. Sinks can have one or more HDMI/HDCP receivers. Repeaters sit between Sources and Sinks. They accept content, decrypt it, then re-encrypt and transmit. Internally, a Repeater may provide signal processing, such as scaling, splitting out audio for use in an analog audio playback system, or splitting the input data stream for simultaneous viewing on multiple displays. Switchers, matrix switchers, and distribution amplifiers are all examples of Repeaters.
HDMI – High-Definition Multimedia Interface - An interface used primarily in consumer electronics for the transmission of uncompressed high definition video, up to 8 channels of audio, and control signals, over a single cable. HDMI is the de facto standard for HDTV displays, Blu-ray Disc players, and other HDTV electronics. Introduced in 2003, the HDMI specification has gone through several revisions: HDMI 1.0 – defined a maximum single-link bandwidth of 165 MHz, supporting resolutions up to 1920x1080 @ 60 Hz; color depth of 24 bits; and up to 8 channels of 24-bit audio. HDCP content protection and CEC – Consumer Electronics Control were optional; HDMI 1.1 – added support for DVD Audio; HDMI 1.2 – added support for SACD – Super Audio CD quality audio. A later revision also added specification for the CEC command set; HDMI 1.3 – increased single-link bandwidth to 340 MHz for signal resolutions beyond 1080p/60. Added support for Deep Color, automatic lip sync correction, and Dolby TrueHD and DTS-HD Master audio.
HD-SDI - High-definition version of SDI specified in SMPTE-292M. This standard transmits audio and video over a single coaxial cable with a data rate of 1.485 Gbit/second.
HDTV - High Definition Television. HDTV refers to a complete product/system with the following minimum performance attributes: a receiver that receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats; a display scanning format with active vertical scanning lines of 720 progressive (720p), 1080 interlaced (1080i), or higher; aspect ratio capabilities for displaying a 16:9 image; receives and reproduces, and/or outputs Dolby Digital audio.
Hertz (Hz) - A unit of frequency; describing the number cycles per second. 1Hz = 1 cycle/second…1MHz = 1 Million cycles/second
High fidelity - Hi fi, accurate, and faithful reproduction of the original. Absence of distortion or enhancements.
High impedance - Hi Z or high Z. A relative term that is different for each application. In video, when the signal is not terminated it has a Hi Z load. Hi Z is typically 800 to 10k ohms or greater.
High pass filter - A circuit that discriminates between high and low frequencies and allows only the high frequencies to pass. Also called a “low cut filter.”
Hooking - See “Bending.”
Horizontal blanking - After making a scan line (left-to-right), the electron beam in a CRT retraces (returns) to the left side of the screen to begin the next line. During retrace time, it is not putting picture information on the screen, so the beam is turned off, or blanked. About 83% of each horizontal cycle is spent writing the line, while 17% is spent retracing the beam to the left before starting the next line. See “Blanking.”
Horizontal Cabling - Telecommunications cabling used to cover a floor area. It extends from the horizontal cross-connect in the telecommunications room to a local access outlet.
Horizontal centering control - Adjusting the horizontal centering control shifts the displayed image left or right on the display screen. Also called “horizontal shift.”
Horizontal Cross-Connect – HC - A patch panel or LAN – Local Area Network panel, used to cross-connect horizontal cables to other cabling within a building or facility.
Horizontal double images - A video problem when the display is split down the middle with two identical but squeezed images displayed on each side of the screen.
Horizontal filtering - In some Extron scan converters and other products, this is a feature that controls the sampling of the horizontal plane, thereby affecting the sharpness or smoothness of the scan-converted picture.
Horizontal rate - Horizontal scanning frequency. The number of complete horizontal lines (trace and retrace) scanned per second. Measured in kHz, the NTSC standard is 15.75 kHz.
Horizontal resolution - The number of vertical lines that can be perceived in a video device.
Horizontal sync - The pulses that control the horizontal scanning of the electron beam in a video device. On connector panels, “H” identifies the connector for horizontal sync, and “H/HV” means it is also used for combined or “composite” horizontal and vertical sync (RGBS).
Hot Plug/Hot Plug Detect - Describes a feature of DVI, HDMI, USB, and other digital technologies which allows a host device, such as a computer, to detect the presence of a new device without intervention by the user. Hot Plug technology allows a new device to be added to a system while it’s still connected to a power source. Once the new device is connected, the Hot Plug Detect circuit, or HPD, senses the new device and tells the rest of the system that the device is ready to either send or receive a data stream.
Hot spot - Commonly seen on high-gain screens and screens designed for slide or movie projection, a hot spot is a circular area where the image is brighter than the rest of the screen. The hot spot is always located along the line of sight, and “moves” with the line of sight.
Hot-swap - The ability to change electronic components, such as circuit boards or peripheral devices, without removing power from the device.
House sync - See “Blackburst.”
HTML - Hypertext Markup Language. A formatting computer language used to create web pages.
HTTP - HyperText Transfer Protocol. A Web protocol based on TCP/IP that is used to retrieve
hypertext objects from remote Web pages.
Hue - (1) Color value or saturation, as opposed to brightness or intensity. (2) Tint control – Hue is the parameter of color that allows us to distinguish between colors. The hue, or tint control, adjusts the amount of color displayed.
Hum - The coupling of an unwanted frequency into other electrical signals. In audio, hum can be heard; in video, it can appear as waves or bars in the picture. Often it is an audible disturbance caused by the power supply, or an improper ground.
Hum bar(s) - Interference in the form of a horizontal bar moving vertically on the display screen. Hum bars can be caused by ground loops.
Humbucker - A transformer used to isolate video signals caused by interference from hum bars or moir?.
I/O - Input/Output. Refers to the flow of information or signals (in or out) with respect to a particular device.
ICIA - International Communications Industries Association. A professional A/V, video, and multimedia industry association. www.infocomm.org
ICT – Image Constraint Token - Part of AACS, the Blu-ray digital rights management system, the Image Constraint Token can cause the output of a Blu-ray Disc player to be down-converted to low-resolution video, similar in quality to a DVD. AACS requires that all components in the display chain, from the source to the display device, to be secured through HDCP or DPCP content protection. If the ICT flag is set and the Blu-ray player is connected to a device that does not support HDCP, for example an analog television or video recorder, the player automatically reduces the high-definition video quality to a maximum of 960x540 pixels before outputting it.
ICWK - Internal Computer Wiring Kit. Custom ICWK kits provide interfacing signals for computers and terminals that have no video display output connector.
ID bit termination - Used to identify what type of display device is attached to a computer-video output port. ID bit termination involves connecting specific data lines or “pins” to the electrical ground. ID bit termination assures that the correct video signals will be sent to the display device. A computer checks for ID bits during the power-up self diagnosis, and sets the video output frequency and resolution based on how the ID bits are set. Some computers will not send any video signal if they do not sense any ID bits on boot-up, so no picture will be displayed. ID bits are also called “sense lines.”
IEC - International Electro-technical Commission. The body that has responsibility for developing international A/V standards. ICIA cooperates with IEC sub-committee SC 60.
IEC connector - The standard AC power connector used on power supplies in computers and other electronic equipment. It accommodates a power cord with a connector on both ends.
IEEE - Institute of Electrical and Electronic Engineers. The IEEE is an industry organization that undertakes the development of standards for electronic interfaces, wireless and wired networks, and related technologies. www.ieee.org.
IEEE 1394 - Institute of Electrical and Electronics Engineers standard 1394. Also known as FireWire (a trademark of Apple) and i.Link (a trademark of Sony), IEEE 1394 is a serial digital format that handles a wide range of data. IEEE 1394 offers peer-to-peer interface capability, so it does not require computer support.
IEEE 802.11 - The Institute for Electrical and Electronics Engineers standard for wireless Ethernet networks. IEEE 802.11 applies to wireless LANs and provides 1 or 2 Mbps transmission in the 2.4 GHz band using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS).
IEEE 802.11a - An extension to 802.11 up to 54 Mbps in the 5GHz band. IEEE 802.11a has a data transmission rate capability sufficient for the delivery of “live” or full motion standard definition video.
IEEE 802.11b - Often called Wi-Fi, 802.11b is backward compatible with 802.11. IEEE 802.11b has a data transmission rate of 11 Mbps, sufficient for most non-motion data transmission applications.
IEEE 802.11g - Applies to wireless LANs and provides 20+ Mbps in the 2.4 GHz band. This is the most recently approved 802.11 standard and offers wireless transmission over relatively short distances at up to 54 megabits per second (Mbps), compared with the 11 megabits per second of the 802.11b standard. Like 802.11b, 802.11g operates in the 2.4 GHz range.
IEEE 802.11n - Upcoming wireless standard that builds upon 802.11 standards by adding Multiple Input Multiple Output (MIMO) technology. MIMO uses multiple transmitter and receiver antennas to increase the data rate, promising between 100-200 Mbps. 802.11n is expected to be ratified in late 2006 or early 2007.
IEEE 802.3 - The Institute for Electrical and Electronics Engineers standard for Ethernet networks.
ILA® - Image Light Amplifier. Used in their large screen projectors, a Hughes-JVC device that uses low-intensity images to modulate high-intensity light through a liquid crystal layer.
Illuminance - The light density (the luminous flux divided by area) shining onto a surface. This is the specification that measures how bright a screen is lit by a projector or ambient light. The unit is lux. 1 lux = 1 lumen/m2.
Image - A reproduction or imitation of a person or thing displayed by any type of visual media.
Impedance - The opposition or load to a signal, measured in ohms and abbreviated W or Z. In video, typical low impedance circuits (low Z) are 600 ohms or less and high impedance circuits (high Z) may be 10 k ohms or greater. Video termination impedance is 75 ohms. See “High impedance” and “Low impedance.”
Impedance matching - Circuits that generate audio or video signals are designed to work with a certain load (impedance). When connecting devices in a system, it is important that the impedance specifications are adhered to. If the impedance of the load is not matched to that of the source, there could be undesirable results, such as loss or distortion of the original signal, reflections, etc.
IMUX - Inverse multiplexer. A unit that combines multiple low bandwidth digital phone lines into a single high bandwidth call.
Index matching gel - A special gel with an index of refraction similar to that of the optical fiber core. It is applied at the fiber endface to minimize loss due to Fresnel reflection in mechanical splices or cleave and crimp connectors.
Index matching materials - Materials with an index of refraction similar to that of the optical fiber core. They are applied at the endfaces of adjoining optical fibers to minimize losses due to Fresnel reflection.
Index of refraction - The ratio of the speed of light in a vacuum to the speed of light in a material. Also known as the refractive index.
Inductor - An electrical component that opposes changes in current flow and stores electrical energy as a magnetic field. Although all wires have inductive properties, an inductor component is usually a coil of wire. Transformers use this same principle.
Infrared (IR) - Light waves just outside the visible spectrum, slightly longer than those visible to the human eye. Infrared light is sometimes filtered out to reduce heat on film or slides. See “Infrared control.”
Infrared control - A wireless medium of remote control, which sends signals to a device via pulses, transmitted in the infrared light spectrum. Its use is restricted to equipment within line-of-sight or reflections off a wall or ceiling. This is sometimes called “IR remote.”
Injection Laser Diode – ILD - A laser in which the lasing, or stimulated emission of coherent light, occurs at the p-n junction of a semiconductor.
Inline splice closure - An enclosure which houses the spliced fiber optic cable and provides cable ports at opposite ends.
Innerduct - A duct, usually non-metallic, that may be placed within cable trays or HVAC ducts, to be used as conduit for installation of fiber optic cables.
Input sensitivity - The minimum input level signal required to output a specified output level.
Insertion loss - The loss of optical power as a result of incorporating components such as connectors, couplers, or splices into an optical fiber system.
Inspection scope - A microscope specifically for inspecting fiber optic connectors.
Interbuilding backbone - A backbone network that provides communication between buildings, such as on a university or corporate campus, or military installation.
Interface - (noun) A device or module that operates as a link between dissimilar modules, usually because those modules cannot communicate directly with each other. An interface may act as a translator or interpreter and could be in the form of hardware and/or software. A computer video interface allows computer-video signals to be used by large screen video displays
Interlacing - A video frame is made up of two fields. Interlacing is the process of scanning the picture onto a video screen whereby the lines of one scanned field fall evenly between the lines of the preceding field.
Interleaving - The process of assigning consecutive physical memory addresses alternately between two memory controllers to increase the effective transfer rate.
Intermediate Cross-Connect – IC - A cross-connect, usually a patch panel, used to provide backbone cabling between the MC - Main Cross-Connect and HC - Horizontal Cross-Connect.
Intermediate Distribution Frame – IDF - In telecommunications applications, a metal rack, located in an equipment room or closet, that provides connection between interbuilding cabling and the intrabuilding cabling.
Intersymbol interference - ISI - In fiber optics, the interference between digital bits in a digital stream caused by pulse spreading in an optical fiber.
Intrabuilding backbone - The backbone network within a building that provides communications to individual offices and users.
Intrinsic Losses - Losses due to inherent differences in the characteristics of the optical fibers being spliced.
IP Internet Protocol. - The protocol or standard used to send information from one computer to another on the Internet.
IP address - A unique, 32-bit binary number (12 digit decimal number—xxx.xxx.xxx.xxx) based on version 4 of the internet protocol (IPv4) that identifies each sender and each receiver of information connected to a LAN, WAN, or the Internet. IP addresses can be static (see “Static IP”) or dynamic (see “DHCP”).
IP Link™ - Extron’s high performance IP integration technology specifically engineered to meet the needs of professional A/V environments.
IP netmask - A 32-bit binary number (12 digit decimal number—xxx.xxx.xxx.xxx) used on subnets (smaller, local networks) to help the router determine which network traffic gets routed internally to local computers and which network traffic goes out on the Internet.
IPv4 - Based on version 4 of the Internet Protocol described in IETF RFC 791, which was first published in September, 1981.
IPX - Internetwork Packet Exchange Protocol. Commonly used over Novell Netware and Microsoft Windows networks.
IR learning - The ability of a device to receive and store infrared commands for other devices, such as the projector. Each command is assigned to a system operation (such as selecting an input). When an operation is executed, the associated (learned) command is then transmitted through an IR emitter or broadcaster to the projector, where it is executed. For example, if input #3 is S-video, selecting that input also sends a signal to the projector to switch to S-video mode.
IR library - Sets of infrared commands for video projectors are available at the Extron Web site (www.extron.com).
IRE - Institute of Radio Engineers. Now called IEEE, the Institute of Electrical and Electronic Engineers. See “IEEE.”
IRE scale - An oscilloscope scale that applies to composite video levels. Typically, there are 140 IRE units in one volt (1 IRE = 7.14 mV). This makes luma level values easier to communicate. The amplitude of the video signal from blanking (zero volts) to peak white is 0.714286 volts or 100 IRE units. Sync signals extend from blanking to 1.285714 volts/40 IRE units.
ISDN - Integrated Services Digital Network. An international communications standard for sending voice, video, and data digitally over telephone lines. ISDN uses special wires and can transfer at rates of 64,000 bits per second. Another version called B-ISDN uses fiber optics and can transfer at 1.5 megabits per second.
ITS - Information Transport System or Intelligent Traffic System
ITU - International Telecommunication Union. Formerly known as the CCIR (Comit? Consultatif International des Radiocommunications) or International Radio Consultative Committee. A global organization responsible for establishing television standards.
ITU-R BT.601 - Formerly known as CCIR 601. A serial digital form of component video developed by the International Telecommunication Union for the digitization of color video signals. ITU-R BT.601 is the digital equivalent to Y, R-Y, B-Y, component analog video, and is transmitted on one coax cable instead of three. It is also called 4:2:2, which refers to the number of samples taken from each of the video channels: for every four samples of the Y (luminance) channel, the two color difference channels, R-Y and B-Y, are sampled twice.
Jacket - Outer protective covering of a wire or cable.
Jaggies - A video problem in which stairstep-like lines appear where there should be straight-angled lines or smooth curves. See “Aliasing.”
Jitter - A video problem in which the displayed image is unstable or appears to shake.
Jitter - The deviation of a signal’s timing transitions in relationship to their ideal positions. Jitter can occur over long lengths of low quality cable, or through the cumulative effect caused by cascading several digital devices in line between the source and destination.
JPEG - Joint Photographic Experts Group. A committee formed as a joint effort between the International Standards Organization (ISO) and CCITT that developed a standard for the still digital image compression/decompression for use in computer systems. File compression standard. The JPEG image size may be reduced by as much as 30:1 with some loss of data. It does not work well with line art, text, or vector graphics. The file extension is “.jpg.
Judder - A distracting side effect of 3:2 Pulldown Detection or “Inverse 3:2 Pulldown” that occurs as a result of every other film frame lasting 1/60 of a second longer than the previous one. Extron’s True Rate™ eliminates this effect by causing the video display rate to increase from 60 fields per second to 72 fields per second.
Kilo. - An abbreviation for 1,000. A kilobyte is 1,000 bytes. Because numbers used in computer RAM sizes are in binary, the closest number is used. When talking about memory size, the numbers are rounded off (e.g. 1 kbyte is really 1,024 bytes).
Kell factor - The ratio between the measured number of TV lines and the pixel count of a fixed pixel video device. It equals 0.7. For example, a DVD picture with 720 pixels in the horizontal direction is equivalent to about 500 TV lines (720 x 0.7=500) of resolution.
Kelvin - An absolute scale of temperature measurement typically used to describe the color of light, expressed in “degrees Kelvin.” The lower the number, the “warmer” or redder the color of the light; a higher number indicates a “colder”, or bluer, light source. Also see “Color Temperature.”
Kevlar® - A brand name from DuPont for aramid yarn, used in the construction of cables to provide strength and strain relief.
Key - (1) Also called key source or key cut. A signal that can be used to electronically cut a hole in a video picture to allow for insertion of other elements such as text or another video image. The key signal is a switching or gating signal for controlling a video mixer that switches or mixes between the background video and the inserted element. (2) The composite effect created by cutting a hole in one image and inserting another image into the hole.
Key fill - In key effects, the video signal that is said to fill the hole cut in the background video by the key source.
Keyer - An electronic circuit that creates a control signal to control a video multiplier based on selective information contained in a video signal.
Keys - See “KSV”
Keystone effect - A distorted picture where one edge is not the same dimension as the opposite edge, producing a tapered or wedge shape. Typically, this results when the image is projected to the screen at an angle. In stone buildings, the tapered stone at the top of an arch is the key that prevents the arch from falling.
kHz - Kilohertz. One thousand cycles per second (hertz).
KSV – Key Selection Vector - A unique numerical key used in content protection or digital rights management schemes such as HDCP. Keys are used to authenticate devices connected to one another, to ensure that a source is connected to a display and not a digital recording device.
Lambert - A unit of measure expressing the intensity of light reflected off an object. 1 lambert = 0.318 foot-candles per square centimeter.
LAN - Local Area Network. A local area network is a group of computers and associated devices that share a common communications line and typically share the resources of a single processor or server within a small geographic area (for example, within an office building).
Lapping film - Sheets of film used for polishing ferrule endfaces, comprising a film backing with mineral particles at various ratings for grit or coarseness.
Laser - Light Amplification by Stimulated Emission of Radiation. An optical source that generates coherent light within a narrow band of wavelengths.
Laser chirp - A sudden change in the center wavelength of a laser, caused by reflected or crosstalk optical energy entering the lasing chamber.
Laser-Optimized Multimode Fiber - A multimode fiber with higher bandwidth than legacy multimode fiber, designed for transmission with laser based sources such as VCSEL.
Latency - The amount of time it takes for a data packet (i.e., a unit of data) to move across a network connection. Latency and bandwidth are the two factors that determine the speed of a network connection.
LBC - Laptop Breakout Cable. The Extron cable that connects a computer laptop to an Extron computer-video interface.
LCD - Liquid Crystal Display. A panel that utilizes two transparent sheets of polarizing material with a liquid containing rod-shaped crystals between them. When a current is applied to specific pixel-like areas, those crystals align to create dark images. The dark areas are combined with light areas to create text and images on the panel. LCD panels do not emit light but are often back-lit or side-lit for better viewing.
LCD projector - Utilizing LCD panel technology, these projectors separate the red, green, and blue information to three different LCD panels. Since LCD panels do not produce color, the appropriate colored light is then passed through each panel and combined to exit through the projector lens and onto a viewing screen.
LCoS - Liquid Crystal on Silicon. This is a reflective display technology where one glass substrate is attached to a silicon chip which is coated with crystals. The chip contains the control circuitry.
Lenticular screen - A screen surface characterized by silvered or aluminized embossing, designed to reflect maximum light over wide horizontal and narrow vertical angles. It must be held very flat to avoid hot spots. A large series of parallel lenticulations cut vertically into the screen surface to improve horizontal dispersion.
Level - The relative intensity of an audio or video source.
Level control - The level control on some interface products is similar to the contrast control on a data monitor. It can either increase or decrease the output signal level from the interface to a data monitor or projector. This results in greater or less contrast in the picture.
Light - The region of the electromagnetic spectrum that can be perceived by human vision, also known as the visible spectrum, which covers the wavelength range between about 0.4 µm to 0.7 µm. In laser and optical communications, this term denotes a broader portion of the electromagnetic spectrum, from the near-ultraviolet region of approximately 0.3 µm, through the visible region, and into the infrared region to 30 µm.
Light Emitting Diode – LED - A semiconductor device that emits incoherent, narrow-spectrum light within the p-n junction.
Light level - The intensity of a given lighting situation as measured in foot-candles (Ft-c).
Light source - In fiber optics, a generic term for the optical signal transmitter in an optical loss test set - OLTS.
Lightguide - Also known as an optical waveguide or optical fiber, a glass or plastic fiber with the ability to guide light along its axis. It comprises a core at the center, surrounded by a cladding with a lower refractive index to keep the light within the core through total internal reflection.
Limiter - Audio circuit or device that prevents the signal from reaching a level where audible distortion can occur.
Line driver - A signal amplifier used to extend a video signal over extended distances. Similar in function to a distribution amplifier (DA), with one input and one output
Line level - Audio signal industry-referenced at 600 ohms, 0 dB. Consumer systems may use a different reference.
Line out - Audio output. In consumer systems, this may be 10,000-50,000 ohms, at -10 dB or -20 dB.
Line voltage - Alternating current (AC) at the level typically found in the home.
Linearity - The ability of a display device to produce an object the same size anywhere on the screen. For example, poor linearity may show the same line of text one size when it is at the top of the screen but a different size when it is at the bottom of the screen.
Link - An optical cable with connectors attached to the transmitter and receiver.
Listening plane - In acoustics, the intersection of the audio field (the horizontal plane) with the listener’s ear.
Logarithm - An exponent used in mathematical equations to express the level of a variable quantity (or, the power to which a number must be raised to produce a specific result).
Loop-through - A feature that allows the video signal to be passed through a device relatively unprocessed and sent to a local monitor or other device. The loop-through is separate from the circuits that process a signal for output to the main presentation or recording device(s). Loop-through connections are found on some scan converters and scalers. (Loop-out)
Loose buffer cable - A type of fiber optic cable in which the fiber is encased within a loosely surrounded buffer tube underneath the jacketing. The tube is usually for protection in outdoor installations.
Loose Tube Gel Filled – LTGF - A Loose Buffer Cable that is filled with a insulating gel material.
Loss - In fiber optics, the loss of optical power in connectors, splices, and fiber defects as light passes through a fiber optic system.
Loss Budget - A specified, maximum tolerable loss of optical power, or attenuation of light, as it passes through a fiber optic system.
Lossless - When using compression to reduce text and/or graphic files, some techniques discard data in the process. Methods that compress files without losing data are called lossless.
Lossy - A term to describe compression techniques that throw away data as part of the process. The more data loss, the smaller the file, and the lower the quality (grainy or jagged edged) of the image. Lossy compression methods include JPEG and MPEG. Note: with JPEG, high means high compression (greater loss) and low means low compression (less loss).
Loudness - The sound pressure level (SPL) of a standard sound. Loudness is the perception of the strength or weakness of a sound wave resulting from the amount of sound pressure level produced. Sound waves that have more intensity or larger variations in air pressure produce louder sounds. Low-intensity sound waves with smaller fluctuations in air pressure produce quieter sounds.
Loudspeaker - An electro-acoustic transducer that converts electrical audio signals at its input to audible sound waves at its output.
Low impedance - The condition where the source or load is at a lower impedance than the characteristic impedance of the cable. Low source impedance is common; low load impedance is usually a fault condition. Example: 30-600 ohms.
Low pass filter - A circuit that discriminates between low frequencies and high frequencies and allows only the low frequencies to pass. For example, a low pass filter design for a subwoofer, set at 80 Hz, would allow the audio signals below 80 Hz to pass through to the speaker, and attenuate the portion of the signal above 80Hz.
LPCM - Linear PCM - A specific method of pulse code modulation that is used to represent an analog waveform as a sequence of amplitude values. LPCM has been defined as part of the DVD and Blu-ray Disc standards, and is also used by HDMI. See “PCM.”
LSFOH - Low Smoke and Fumes Zero Halogen. IEC designation of a cable jacket that passed IEC 332-3 flame test, IEC 61034 smoke test, and IEC 754-1 corrosivity test.
Lucent Connector - LC - A high-density optical fiber connector becoming more popular and are replacing the popular SC due to the smaller size.`. LCs are used on Extron fiber optic products.
Luma - Also called Luminance. The photometric radiance of a light source. The luma signal represents brightness in a video picture. Luma is any value between black and white and is abbreviated as “Y.” See “Chroma.”
Luma (luminance) key - A picture-combining effect where the Y (luminance) portion of one video signal is replaced with video from another source. Luma keys are typically used to insert white text into a color video image.
Luma delay - A video problem in which the intensity of an object or area is shifted slightly to the right of the color. The color occurs in the correct area of the displayed image, but the luma (intensity) starts later.
Lumen - The unit of measure for light coming out of a light source, such as a projector. CRT projectors usually use a 10% white window pattern for measurement purposes, while LCD and DLP projectors use a 100% white window (ANSI standard). Also see “ANSI Lumens.”
Luminance - The light density coming out of a surface. This is the specification for measuring the brightness of a projection screen or a CRT monitor’s tube surface. The SI unit is “cd/m2” (candles per square meter). It is also called “nit” in the US system and “footlambert” in the English system. 1 foot-lambert = 3.426 cd/m2.
Luminous flux - The total amount of light coming from a light source, measured in lumens.
LVDS - Low Voltage Differential Signal. A signal transmission standard developed for the connection of laptop computers to their local LCD displays. National Semiconductor is the manufacturer that is promoting this standard. SGI used LVDS on the 320 and 540 NT Visual Workstations for connection to their 1600SW series, 16 x 9 aspect ratio, LCD monitor.
Mega. - A prefix for one million.
MAAP - Mini Architectural Adapter Plates. Compact mountable metal plates available in hundreds of models offering popular pass-through audio, video, phone, data, power, and control connectors. Active MAAPs are also available for power, control, and long distance signal transmission. Along with mounting options for maximum flexibility in placing connectors and controls within reach, these interchangeable components fit together to create an attractive and completely customizable A/V connectivity solution..
MAC address - Media Access Control. A unique hardware number given to devices that connect to the Internet. When your computer or networking device (router, hub, interface, etc.) is connected to the Internet, a table (see “ARP”) relates the device’s IP address to its corresponding physical (MAC) address on the LAN.
Macrobending - A term that describes a macroscopic deviation of an optical fiber’s axis from a straight line due to bending, to the extent that optical loss occurs. Excessive macrobending enables the light traveling down the core to strike the core-cladding boundary at an angle of incidence less than the critical angle. A portion of the light transmits into the core and is lost.
Magnetic deflection - A method of altering the path of an object (such as an electronic beam) with a magnetic field. CRTs have magnetic coils that carry currents that create magnetic fields that control the path of the electron beam. Also called Magnetic focus.
Magnetic focus - See “Magnetic deflection.”
Main Cross-Connect – MC - The central portion of a facility’s backbone cabling that provides connectivity between equipment rooms, entrance facilities, horizontal cross-connects, and intermediate cross-connects. It usually consists of a distribution of patch panel.
Main Distribution Frame – MDF - A signal distribution frame that connects lines from the outside and lines on the inside.
Matched-Clad Optical Fiber - A single-mode optical fiber with a cladding of uniform refractive index, favored for being less susceptible to bending and splice losses.
Matrix - An electronic device that accepts and distributes video (and/or audio) signals selected from multiple inputs and multiple outputs. See “Matrix switcher.”
Matrix mixer - Similar to a matrix switcher, but with additional signal processing features, such as equalization (EQ), compression, and level/gain controls on the inputs and outputs.
Matrix switcher - A means of selecting an input source and connecting it to one or more outputs. Like a regular switcher, but with multiple inputs and multiple outputs.
Matte white - A screen with a flat, dull surface for even reflection over wide viewing angles.
MAV - The Extron acronym for matrix audio/video (switcher).
MB - Megabyte. A megabyte is actually 1,048,576 bytes, or roughly 1 million bytes
MBC - Monitor Breakout Cable. A cable used to view a computer signal on a local monitor or terminal while routing the same signal to a new source, such as a data projector or monitor. An MBC provides three connections in the form of a “Y” cable, a “T” cable, or through a buffer in an enclosure box.
MBC power connector - Some of the Extron MBC high resolution buffers require power. The miniature power plug attached to some MBC cables plugs into the MBC power jack on the interface.
Mbps - Megabits per second. One million bits per second; a unit of measurement for data transmission.
Mechanical splice - A splice between optical fibers accomplished by using a mechanical fixture and an index gel, rather than by thermal fusion.
MediaLink™ - Extron’s MediaLink System is a family of easy-to-use and inexpensive products that work together to control A/V equipment in any small, one-projector classroom, boardroom, or auditorium.
Megapixel - In digital imaging devices, megapixels define the resolution range when the number of pixels is equal to or greater than 1 million pixels. For example, SXGA is 1280 x 1024, or 1,310,720 pixels. This could be called a 1.3-megapixel device.
Messenger wire - A wire that is used as the supporting element of a suspended aerial cable. This wire may be an integral part of, or external to the cable.
MFTA - Multi-Frequency Termination Adapter. A single termination device with selectable frequencies for different applications.
MHz - Megahertz. One million hertz (cycles per second). Video bandwidth is measured in megahertz.
Microbend - A localized defect in an optical fiber at the core-cladding boundary, caused by mechanical stress that results in sharp, microscopic curvatures in the fiber.
Microbending loss - Loss in an optical fiber due to sharp, microscopic curvatures, caused by imperfections in fiber coating, cabling, packaging, and installation, such as cinching fibers too tightly with a tie wrap.
Micron - One millionth (10e-6) of a meter.
Mid-Entry - In fiber optics, the opening up of a fiber optic cable mid-span in order to access the fibers inside.
Mid-range - The range of audio frequencies, 250 Hz to 5000 Hz, to which the human ear is most sensitive. Mid-range frequencies give sound its energy.
Military tactical cable - Heavy-duty cable designed for rugged installations in adverse environments.
Milli - m. Abbreviation for one one-thousandth. Example: 1 ms = 1 millisecond or 1/1000 second.
MIMO - Multiple Input Multiple Output antenna technology. In 802.11n. This technology promises to deliver up to 8x coverage and up to 6x speed of current 802.11g networks.
Mini zipcord - A 2.5 mm diameter fiber optic cable with two jacketed fibers that can be separated.
MIPS - Million Instructions Per Second. The rate at which a computer executes instructions.
Modal bandwidth - In fiber optics, the bandwidth-length product of an optical fiber due to modal dispersion measured in MHz-km.
Modal dispersion - In fiber optics, the dispersion of a single optical pulse into various modes which arrive at the light receiving device at different times. This limits the performance of multimode optical fiber.
Mode - A path for light within an optical fiber. Single-mode fiber comprises a single path, while in multimode fiber, there are multiple light paths.
Mode Field Diameter – MFD - A measure of the spot size or beam width of light propagating in a single-mode optical fiber. Usually this is 20% larger than the diameter of the core.
Mode filter - A device that removes higher-order modes in multimode fiber.
Modem - Modulator/demodulator. A device that puts information on a carrier signal and transmits it over a (phone) network. The same device receives such signals and demodulates, or separates the information from the carrier. A modem connects computers with other communication devices through ordinary phone lines.
Modulation - The process of adding an information signal to a carrier frequency to allow it to be transmitted. Thus, the carrier is modulated by the information signal, as in a modem.
Moir - A pattern resulting from a combination of other patterns. In video, this is usually an undesirable pattern caused by an unwanted signal interfering with the desired signal. This may appear as a wavy motion.
Momentary contact - A non-latching contact closure that lasts as long as it is held in place.
Momentary switch - A switch that returns to its normal circuit condition when the actuating force is removed.
Monitor - (1) A TV that receives a video signal directly from an external source, such as a VCR, camera, or separate TV tuner to produce a high-quality picture. (2) A video display used with closed circuit TV equipment. (3) A device used to display computer text and graphics.
Monitor/receiver - A TV having RF tuning circuits to receive broadcast signals for viewing.
Monochrome - One color, usually interpreted as black and white. In computer CRTs, it is any single color with black.
Monochrome composite output - Provides a monochrome video output with combined horizontal and vertical sync for composite video with all the shades of the computer’s monochrome, 8-, 16-, or 64color display adapter card output signal.
Monochrome signal - A video signal having one color, usually a black and white signal, or sometimes the luma portion of a composite or component color signal.
MPEG - Motion Picture Experts Group. A standards committee under the auspices of the International Standards Organization working on algorithm standards that allow digital compression, storage and transmission of moving image information such as motion video, CD-quality audio, and control data at CD-ROM bandwidth. The MPEG algorithm provides inter-frame compression of video images and can have an effective compression rate of 100:1 to 200:1.
MPEG-2 - The video compression algorithm used for DVD-Video, Digital Broadcast Satellite (DBS), and Digital TV (including HDTV) delivery systems.
MPEG-4 - Similar to MPEG-2, but with a much greater ability to scale to different compression rates and resolutions. MPEG-4 is suitable for applications ranging from low bit-rate streaming video applications for videoconferencing and cell phone video delivery, to high bit-rate high definition television production systems.
MTBF - Mean Time Between Failures. A basic measure of reliability for repairable items. It can be described as the number of hours that pass before a component, assembly, or system fails. Also (MTBR) Mean Time Between Repairs.
MTP - Extron’s acronym for it’s Mini Twisted Pair line of products.
MTS - Multichannel Television Sound. One of the first stereo sound systems developed for television. MTS consists of two independent singles each carrying a discrete channel. One channel provides stereo sound by providing left/right channel difference signals relative to transmitted mono audio track. The second carrier carries the Secondary Audio Program (SAP) which is used for a second language or for Descriptive Video, a descriptive commentary for the vision impaired.
Multimode Fiber – MMF - An optical fiber that allows for the propagation of more than one mode or light path. It is commonly used with LED light sources for shorter distance links.
Multiple Termination Plug – MTP - A small form factor – SFF plug for multiple fibers.
Multipoint - When more than two locations are connected for a videoconference using a bridge. Usually multipoint switching is done by video-follow-audio, such that the person speaking is automatically seen by the other conference site(s).
MUX - Short for multiplexer. A device that combine multiple signals for transmission over a single line. The signals are demultiplexed (DEMUX’d), or separated, at the receiving end.
NAB - National Association of Broadcasters, the body that sets standards for US broadcast stations. www.nab.org
Nanometer - nm - One billionth (10e-9) of a meter.
Native Resolution - Refers to the single fixed resolution of an LCD, plasma, or other fixed matrix display. An image said to match the native resolution of a display is one where pixels between the image source and display are perfectly aligned and require no scaling or other signal processing.
Near end - In videoconferencing, the party or group at the local end of the connection.
NEC - National Electrical Code. The National Electrical Code is the product and responsibility of the National Fire Protection Association (NFPA). The NEC covers the installation of electric conductors and equipment in public and private buildings and other premises, such as yards, parking lots, carnivals, etc. In general, the NEC is used in every state in the nation and provides safeguards of persons and property from hazards arising from the use of electricity.
Networking - Two or more devices (or people) communicating with each other and sharing
NEXT - Near-End Crosstalk. A measure of interference between the conductors of a cable. A measure of the unwanted signal coupling from a transmitter at the near end (source end) into neighboring pairs measured at the near end. NEXT loss is expressed in decibels relative to the received signal level.
NIC - Network Interface Card. A piece of hardware, usually a peripheral card, that interfaces a computer to a network.
Nit - A unit of measurement of luminance, or the intensity of visible light, where one nit is equal to one candela per square meter. Nits are used to describe the brightness of computer displays, such as LCD and CRT monitors.
Node - One specific point or connected location on a network (i.e., a client or print server).
Noise - Any unwanted signal that adversely affects the quality of the picture or sound.
Noise criteria - Abbreviated “NC”. An NC level is a standard that describes the relative loudness of a room or space, across a range of frequencies. The NC level illustrates the extent to which ambient noise interferes with speech intelligibility. NC should be considered for any project where excessive noise would be irritating to the users, especially where speech intelligibility is important.
Noise gate - An audio processing device that reduces background noise by muting a sound signal when it falls below a pre-determined level, and restores it when the level increases again. For example, in a board room where multiple microphones are installed, a noise gate may be used to mute the microphones of those not currently speaking, in order to eliminate disturbing background noise in the sound support system.
Noise reduction - Any technique for reducing the amount of undesired noise in an audio signal. A common technique is called “companding”, a circuit that combines a COMPressor and an exPANDer. The signal is compressed before recording (which maximizes the signal to noise ratio), then expanded during played back. As the signal is expanded, noise tends to be “pushed down,” resulting in a quieter signal.
Noise-canceling - A microphone designed to cancel ambient noise so that it will not be broadcast or recorded. The housing of the microphone allows noise to reach both sides of the diaphragm simultaneously, one side canceling the other out. A close speaking voice strikes the diaphragm on only one side, generating a stronger signal with less background noise.
Nominal level - The signal strength level at which a product is designed to operate for optimized performance. Most of the specifications are tested at the nominal level and all of the built-in signal meter reference levels (e.g. 0dB) are set at the nominal level. A device’s input nominal level should match the nominal level of the source device it is connected to, while the output nominal level of a device should match the nominal level of the destination device it is connected to. The most commonly used nominal levels for video and audio are: video, 1Vp-p (video with sync), 0.7Vp-p (video without sync), 0.3Vp-p (chroma); audio, +4dBu (1.23V, pro audio line level), -10dBV (316mV, consumer audio line level), -60dBV (1mV, mic level).
Non-blocking matrix switchers - These are true matrix switchers allowing any input to switch to any or all outputs. They have no switching limitations contingent on hardware or software. Extron builds only true matrix switchers with all switching paths available at all times; there is no blocking.
Non-composite video signal - A video signal that contains picture and blanking information only with no sync information.
Non-interlaced - Also called progressive scan. A method by which all the video scan lines are presented on the screen in one pass instead of two. Also see “Interlacing” and “Progressive Scan.”
Non-plenum - A cable that does not meet CMP or CL2P flame test requirements.
Non-segmented - A system of video recording that uses one head to scan one field of video onto the tape.
Normally closed contact - Relay or switch contacts that are closed when the relay is not activated.
Normally open contact - Relay or switch contacts that are open when the relay is not activated.
Notch filter - A circuit that effectively separates the NTSC black and white information from the color 3.58 MHz carrier signal. The name is based on the fact that the circuit takes a notch out of the frequency band.
Notch filter - A band rejection filter that produces a sharp notch in the frequency response of a system, thus reducing the gain or amplitude of a narrow band of frequencies centered on a given frequency. In audio, notch filters are used to help eliminate feedback by reducing gain in a narrow band of frequency.
NSCA - National Systems Contractors Association. The NSCA is an international trade association of companies specializing in audio, video, security/life safety, presentation, lighting, or other low-voltage systems. This association offers an annual expo. www.nsca.org
NTSC - The color video standard used in North America and some other parts of the world created by the National Television Standards Committee in the 1950s. A color signal must be compatible with black-and-white TV sets. NTSC utilizes an interlaced video signals, 525 lines of resolution with a refresh rate of 60 fields per second (60 Hz). Each frame is comprised of two fields of 262.5 lines each, running at an effective rate of 30 frames per second.
Numerical Aperture – NA - In fiber optics, the sine of the acceptance angle, a critically defined angle measurement from the center axis of the fiber. Incoming light must be directed below this angle in order to enter the core of the fiber and propagate along its length through total internal reflection.
Nyquist frequency - The highest frequency that can be reproduced accurately when a signal is digitally encoded at a given sample rate. Theoretically, the Nyquist frequency is half of the sampling rate. For example, when a digital recording uses a sampling rate of 44.1kHz, the Nyquist frequency is 22.050kHz. If a signal being sampled contains frequency components that are above the Nyquist limit, aliasing (stair-stepping) will be introduced in the digital representation of the signal unless those frequencies are filtered out prior to digital encoding.
NZDS - Non-Zero Dispersion Shifted fiber. A single-mode fiber with the zero-dispersion wavelength slightly beyond the spectral region for transmission in order to improve performance.
OCR - Optical Character Reader or Optical Character Recognition. Hardware and software that reads characters as images and converts them into text to be used in a computer.
Octave - A doubling or halving of a frequency. For example, 200 Hz is one octave higher than 100 Hz; 50 Hz is one octave lower.
Ohm - The unit of electrical resistance, transmitting a current of 1 amp when subjected to a potential difference of 1 volt. Represented by W or Z.
Optical Link - A single fiber optic signal path or point-to-point fiber optic connection between a transmitter and receiver, including connectors, fiber, splices, and other fiber optic components in the path.
Optical Loss Test Set – OLTS - Test equipment for single-mode or multimode optical fiber comprising a light source and a power meter, used to measure optical signal loss along the fiber and any connectors in between.
Optical Return Loss – ORL - A measure, in dB, of the amount of optical power reflected within a fiber optic pathway due to the fiber and optical components.
Optical Time Domain Reflectometer – OTDR - An instrument in fiber optics used to measure backscattered light in the detection of defects along a span of optical fiber.
Optical Waveguide - In fiber optics, a structure than restricts the flow of light to travel over a desired path, such as an optical fiber.
Oscilloscope - A test device that allows measurement of electronic signals by displaying the waveform on a CRT screen.
Output Power - In fiber optics, this is the radiant power, expressed in watts or dBm.
Outside Plant – OSP - In a telecommunications network, this is the portion that is situated mainly outdoors. This includes patch panels, closure, pedestals, cabling, poles, towers, repeaters, and other equipment.
Overfilled Launch Condition – OFL - In fiber optics, a condition where the incoming light has a spot size and numerical aperture–NA larger than acceptable by the fiber. Typically associated with LED transmission and multimode cable.
Overscan - The result of the TV scan lines exceeding the boundaries of the display screen.
Packet - A collection of network data sent at once from one network node to another.
PAL - Phase Alternate Line. A television standard in which the phase of the color carrier is alternated from line to line. It takes four full pictures (8 fields) for the color-to-horizontal phase relationship to return to the reference point. This alternation helps cancel out phase errors. For this reason, the hue control is not needed on a PAL TV set. PAL, in many transmission forms, is widely used in Western Europe, Australia, Africa, the Middle East, and Micronesia. PAL uses 625-line, 50-field (25 fps) composite color transmission system.
PanelLink® - Silicon Image’s TMDS (Transition Minimized Differential Signaling) all-digital video transmission standard. PanelLink technology was designed to provide the bandwidth necessary to support digital displays.
Parametric equalizer - A type of audio equalizer having several “parameters” for control of various filters that can
be applied to audio signals. Parametric equalizers are most widely used in situations where
very fine control over the audio signal is desired, and provide control over gain, Q (Quality factor, a measure of a resonant system), and frequency. (See EQ-Audio)
Passive crossover - A crossover network that divides audio frequencies without any active amplification or buffering components and which uses only resistors, capacitors and inductors.
Passive Optical Network – PON - A fiber optic network comprising single-mode fiber, passive splitters, and passive couplers for a service provider to deliver fiber to the home – FTTH, or fiber to the building – FTTB.
Patch cord - A predetermined length of cable with connectors at both ends, also known as a cable assembly, patch cable, or jumper.
Patch panel - A passive device, typically flat plate holding feed-through connectors, that allows temporary circuit arrangements and rearrangements by simply plugging and unplugging patch cables. In fiber optics, this is also known as a cross-connect panel, and is used for interconnection of multiple cables or fibers.
PC - Personal Computer or Projector Control.
PCB - Printed Circuit Board.
PCM – Pulse Code Modulation - The digital representation of an analog audio signal. PCM is the standard form of digital audio in computers and the compact disc (CD) “red book” format, as well as the standard used for the audio portion of digital video recording.
PDF - Portable Document Format. A type of format developed by Adobe Systems with which the same file can be opened and viewed on most any computer platform (PC, Mac, Unix). It can also be printed on most any printer (dot matrix, laser, inkjet, PostScript, or non-PostScript). A PDF is a document file in that it includes text and graphics in one file that maintains the appearance of the original.
Peak - The highest level of signal strength, as determined by the height of the signal’s
Peak white - The whitest portion of a picture signal.
Peaking - A means of compensating for mid- and high-frequency RGB video bandwidth response in data monitors and projectors and for signal losses resulting from cable capacitance. The higher the frequency and longer the cable length, the more peaking may be required.
Peaking control - Peaking control on Extron products compensates for mid- and high-frequency RGB video bandwidth response in data monitors and projectors and for signal losses resulting from cable capacitance. When using the peaking control a noticeably sharper picture will be seen on all displays regardless of cable lengths. However, 100% peaking may provide over enhancement on short cable runs. Use the position that produces the sharpest image on the display screen. Also called “sharpness” control.
Peak-to-peak - Abbreviated “p-p.” The difference in amplitude (voltage, for example) between the most positive and the most negative excursions (peaks) of a signal.
Peripheral device - Normally an external device that a CPU communicates with, such as a printer, mouse, disk drive, or interface.
Persistence - In video, persistence is the staying power of a lighted phosphor, since a phosphor begins to dim after being excited by the electron beam. A long-persistence phosphor allows the screen to dim more slowly. Long-persistence phosphors are commonly used for CRT projection in 3D applications.
Phantom power - A standardized method of providing power to condenser microphones using the two signal leads of a balanced audio connection. An international standard, IEC 60268-15, defines three DC voltages, 48 V, 24 V, and 12 V. In professional applications, 48 V Phantom power is the most common.
Phase - The relative timing of one signal to another, usually expressed in degrees of shift.
Phasing adjustment - To properly synchronize an NTSC/PAL video output signal to a genlock signal, a phasing adjustment to the horizontal phase and the subcarrier phase may be required. The horizontal phase difference between these two signals must be set to zero. Likewise, the subcarrier phase difference between these two signals must also be set to zero.
Phone plug - A small, round audio plug used as a speaker connector. Also called 1/4” phone plug.
Phono plug - A plug most often used with line level audio signals. Also known as an RCA plug.
Phosphor - The chemical coating on the inside of the CRT screen that emits light (monochrome or color) when struck by an electron beam. Each dot on the screen is actually a phosphor that glows for a period of time. See “Persistence.”
Photodetector - A device that senses incoming light and outputs an electrical signal in response to the light.
Photon - A elementary unit of light with both waveform and particle properties.
Physical Contact – PC - In fiber optics, the point at which a glass surface, such as that of a fiber, physically touches another glass surface, usually that of a connector.
Physical plant - Infrastructure components including cable, connectors, splices, panels, splitters, repeaters and regenerators necessary to propagate the light signal between the
transmitter and receiver
Picture tube - See “Cathode Ray Tube.”
Pigtail - A short length of cable with one end terminated with a connector and the other end spliced or hard-wired to existing cable or equipment.
Pigtail assembly - A short length of fiber optic cable with one end terminated with a connector, and the other end fixed to a transmitter, receiver, or long length of cable via a splice.
Pin cushion - The inward or outward (curved) appearance of the edges of a display.
PIN Diode - Positive Intrinsic Negative Diode. A type of photodiode, or optical signal transducer that converts light to an electrical signal, used in fiber optic receivers.
Pin out - An illustration or table that names signals, voltages, etc., that are on each pin of a connector or cable.
PIN-FET - Positive Intrinsic Negative Field Effect Transistor. A type of photo-detector or optical signal transducer converts light to an electrical signal, used in fiber optic receivers. The PIN-FET is a hybrid device that combines a PIN diode with a high-speed FET.
Ping - The Packet INternet Groper (ping) command is used to test connectivity between IP devices. The Internet Control Message Protocol (ICMP) echoes Ethernet packets to determine whether a network device is active and what the bidirectional delay is in communicating with it.
Pink noise - A type of random noise that contains an equal amount of energy per octave. The bands 100-200, 800-1600, and 3000-6000 all contain the same amount of energy. Since pink noise is based on octaves rather than individual frequencies, there is no increase in energy in the high octaves. Because of this, and because Real Time Analyzers (RTA) tend to look at octave or 1/3 octave ranges, pink noise is very useful for measuring the frequency response of audio equipment, as well as for determining room response for sound reinforcement applications.
PIP - Picture-in-Picture. A small picture within a larger picture created by scaling down one of the images to make it smaller. Each picture requires a separate video source such as a camera, VCR, or computer. Other forms of PIP displays include Picture-by-Picture (PBP) and Picture-with-Picture (PWP), which are commonly used with 16:9 aspect display devices. PBP and PWP image formats require a separate scaler for each video window.
Pitting - In fiber optics, an undesirable endface polishing condition resulting from the use of lapping film that has been contaminated with fiber optic and grit particles. Pitting can also denote small cracks in the endface due to exposure of cleaning agents to intense light through a fiber.
Pixel - Picture element. A pixel is a single point in a graphic image or screen. Pixels are arranged in rows and columns. See “Pixel resolution.”
Pixel clock - Dot clock. The pixel clock divides the incoming horizontal line of video into pixels. This pixel clock has to be stable (a very small amount of jitter) relative to the incoming video or the picture will not be stored correctly. The higher the frequency of the pixel clock, the more pixels that will appear across the screen (pixel resolution).
Pixel loss - A video problem in which picture information is missing, giving the appearance of specks in the image.
Pixel phase - An adjustment common to scalers and projectors, which adjusts the point in time that a sample is taken in the A-D conversion process. The pixel (or dot) clock in a computer and the pixel clock in a display device may operate at the same frequency for a given resolution and refresh rate, but not necessarily in phase with each other. Pixel phase adjustments are provided on digital monitors and projectors to synchronize the two independent clocks. A test generator like the Extron VTG 300 includes an alternating pixel pattern, which is used to eliminate banding and shimmering artifacts that are symptomatic of pixel phase error.
Pixel resolution - In computer graphics and video images, the number of pixels in the display. For example, a picture with 1,024 x 768 pixels is much sharper, or has higher resolution, than a picture with 640x480 pixels. The total number of pixels is the product of these two numbers.
Plane - In matrix switchers, a plane refers to all of the inputs and outputs of one signal. For example, the red plane would include all of the inputs and outputs for red signals; the blue plane would include all of the blue signals.
Plane breakaway - On matrix switchers, the ability to break one of the planes away from the others. Generally the video, sync, and audio planes will switch the same way (i.e., have the same switching pattern). With plane breakaway, an individual plane can be set up to switch independently of the others.
Plane grouping or I/O grouping - When a number of independent planes on a matrix switcher are all grouped so they switch in unison.
Plastic Optical Fibers - Optical fibers in which the core and cladding are made of plastic. The diameter of the core is often larger than that of glass fiber.
Plenum cable - Cable having a covering (jacket) that meets UL specifications for resistance to fire.
Plug - In A/V and fiber optics, this is also known as the male connector.
PLUGE - Picture Line Up Generation Equipment. This is the name of a test pattern that assists in properly setting picture black level. PLUGE can be part of many test patterns. The phrase and origination of the test signal are both credited to the British Broadcasting Company.
Point-to-point - A videoconference between two locations, like a telephone call. Also see “Multipoint.”
Polarity - The positive and negative orientation of a signal. Polarity usually refers to the direction or a level with respect to a reference (e.g. positive sync polarity means that sync occurs when the signal is going in the positive direction).
Polishing paper - A plastic polishing sheet for optical fiber or connector endfaces with fine grit on one side.
Polishing puck - A fixture for optical fiber endface polishing, used to support a fiber optic connector ferrule in place, properly aligned to the lapping film.
Polyethylene - One of the Polyolefins used for Insulation of Non Plenum Wires and also in the Foaming form as Dielectric for all Non Plenum COAX.
Polyolefin - Family of Compounds consisting of Polyethylene , Polypropylene , PolyButylene etc.
Port - A connection for an input or output device. Typical ports found on a computer include serial, parallel, SCSI, disk drive, video, and keyboard ports.
Port number - A preassigned address within a server that provides a direct route from the application to the Transport layer or from the Transport layer to the application of a TCP/IP system.
Potentiometer - A variable resistor. Potentiometers typically have three terminals: the two end terminals, across which the entire resistance appears, and a third terminal, the “wiper”, which moves to a different spot on the resistor as the shaft is turned. In this manner, the resistance between the wiper and one end terminal gets smaller while, at the same time, the resistance between the wiper and the other end gets larger. This allows the potentiometer to be used as a variable voltage divider, for use in attenuators such as volume controls or tone controls.
Power (electrical) - The dissipation of heat by passing a current through a resistance. Measured in watts [W], Power [P] is expressed by ohm’s law from the three variables: voltage [E] current [I] and resistance [R]. That is, P = I2 x R, or, P = E2/R or P = E x I.
Power meter - A device that measures the optical power at the end of a fiber.
Powered Ethernet - A standard (IEEE 802.3af) that provides power to network devices by utilizing the existing Ethernet connection, thereby eliminating the need for dditional, external power supplies.
Preamp - Preamplifier. An electronic circuit that raises a weak signal high enough to be fed into an amplifier.
Presentation device - A general term used to define a video projector, plasma display, presentation monitor, or other large format data display device.
Primary colors - Any set of colors from which other colors can be derived. In video, the primary colors are red, green, and blue. Equal amounts of red, green, and blue make white; the absence of all colors makes black.
Proc amp - See “Processing amplifier.”
Processing amplifier - An electronic device that stabilizes, changes, or rebuilds signals.
Profile Alignment System – PAS - A technique for fusion splicing that employs a CCD camera for precisely aligning the cores of two optical fibers.
Progressive scan - A method by which all the video scan lines are presented on the screen in one pass instead of two. Typically denoted by the letter “p”, as in “480p”, which indicates a signal with 480 active lines running at 60 frames per second. Also see “Non-interlaced.”
Projection - The process of presenting visual media by light transmitted through an optics system to a viewing screen.
PROM - Programmable Read Only Memory. An electronic memory that does not lose its contents when power is removed, and that can be reprogrammed using a special PROM programmer (“burner”). See “EPROM” and “EEPROM.”
Propagation Delay - The amount of time required for a certain amount of data to be transferred over a cable or other medium. Propagation delay is affected by operating temperature, voltage supply, and cable capacitance, as well as by the number of electronic circuits in line between the signal input and final output.
Protocol - A set of agreed-upon standards that define the format, order, timing, handshaking, and error checking method for data transfer between two pieces of equipment.
Pseudorandom noise - A noise that satisfies one or more of the standard tests for statistical randomness. Although it seems to lack any definite pattern, pseudorandom noise consists of a sequence of pulses that will usually repeat itself, albeit after a long time or a long sequence of pulses.
Pulse broadening - An increase in the duration of a pulse.
Pulse spreading - The dispersion of an optical signal as it traverses along an optical fiber. Also known as Pulse Dispersion.
Pulse width - The time during which a source, such as a laser, is in an “on” state.
Pulse width modulation - A powerful technique for controlling analog circuits with a processor’s digital outputs. PWM is employed in a wide variety of applications, including high power switching amplifiers. By controlling analog circuits digitally, system costs and power consumption can be drastically reduced.
PVC - Poly Vinyl Chloride. Used for Insulation of Wires and Jacketing of most Non Plenum Cables.
Q-factor (Quality factor) - A measure of the “quality” of a resonant system. Resonant systems respond to frequencies close to the natural frequency much more strongly than they respond to other frequencies. On a graph of response versus frequency, the bandwidth is defined as the 3 dB change in level besides the center frequency. QS-FPC™
QuickSwitch Front Panel Controller - . This is a front panel controller on Extron matrix switchers. The panel allows easy set up and control of the matrix switchers through a series of buttons on the front panel.
Quad standard - A term used for video products that are compatible with the following four standards: NTSC 3.58, NTSC 4.43, SECAM, and PAL.
Quantization - The process of sampling an analog waveform to convert its voltage levels into digital data.
Quantizing error - Inaccuracies in the digital representation of an analog signal. These errors occur as a result of limitations in the resolution of the digitizing process.
Quantizing noise - The noise (deviation of a signal from its original or correct value) that results from the quantization process. In serial digital video, it is a granular type of noise that occurs only in the presence of a signal.
QUXGA - Quad UXGA, a computer resolution of 3200 x 2400 pixels (four times 1600 x 1200)
QXGA - Quantum extended graphics array. A graphics standard with 2048 x 1536 pixels.
Rack unit - As defined by the Electronics Industries Association (EIA). In reference to product rack height, a unit is a universal measurement: 1.75 inches or 44 mm. 1U (Unit) high refers to 1.75 inches, 2U high refers to 3.5 inches, etc.
RAM - Random Access Memory. RAM is volatile memory that can be written to and read from. RAM is the working memory where active programs and data are stored. RAM normally loses its contents when power is removed. See “PROM.”
Random noise - Also known as “white noise.” A noise signal that never repeats and has a flat frequency spectrum. Random noise can also be a digital pattern that never repeats. Random noise is generally considered to have a Gaussian amplitude distribution, but numerically generated noise can also have a flat amplitude distribution. The amplitude of random noise is normally measured as the rms value.
Raster - A raster is the series of scan lines that make up a TV picture or a computer’s display. The term raster line is the same as scan line. All of the scan lines that make up a frame of video form a raster. Lines and rows of dots such as those on the illuminated face of a video screen. A matrix of pixels or the scan lines on a CRT.
RC network - An electrical network that is constructed using a resistor and capacitor in parallel, and acts as an effective high-pass filter.
RCA plug - A connector type most often used with line level audio signals and composite video. (Phono)
Real-time analyzer - A device that measures room acoustics in real time, typically using pink noise. See “Pink Noise.”
Rear projection screen - A translucent screen with a special coating that allows an image to be projected through the screen from the rear, instead of from the front. Also see “Front projection screen.”
Rear screen projection - A presentation method in which the image is projected through a translucent screen toward the audience.
Receive – Rx - In fiber optics, to detect an optical signal from a fiber optic cable using a photodetector, such as a PIN diode, APD, or PIN-FET, and convert it to an electrical signal. The receive port of a transceiver.
Receiver - In fiber optics, this is the device at the receiving end of a fiber optic system that converts an optical signal to an electrical signal, and houses the necessary signal processing to output telecommunications, data, or A/V signals.
Receiver sensitivity - The minimum optical power necessary for the photodetector in a receiver to achieve a specified BER - Bit Error Rate or other performance specification such as signal-tonoise ratio.
Reclocking - Reclocking is a process that is used to restore the amplitude, rise and fall times, and clock rate attributes of a digital signal. Reclocking can add a small amount of time delay to the signal.
Reconstruction filter - A lowpass filter used to reduce aliasing and to soften the digital edges in an image. Without the reconstruction filter, images may have a Moir? pattern. On Extron products, this feature, referred to as Filter Mode, is selected to be either “ON” or “OFF.” The Filter Mode is intended for use with digital projectors. The feature should, however, be turned off when using CRT displays.
Reflectance - In fiber optics, the ratio of optical power reflected to the incident power at a connector junction or other component or device. It is expressed as a negative value in decibels– dB.
Reflections - With video signals, reflections can be caused by energy that is not absorbed by the load (or a termination) and is reflected and possibly combined with the original signal. Reflected signals can occur when the impedance does not match (as a result of wrong termination or mixing of cable impedance). Some of the undesirable results of reflection include Y/C delays, color smearing, ringing on luma (but not on color), and ghosts. In fiber optics, abrupt changes in the direction of light at an interface between two dissimilar media so that the light returns to its origin.
Refraction - The change in direction of light as it passes from one medium to another, dissimilar medium. Refraction also occurs as light passes through a graded-index medium in which the refractive index varies within the medium.
Refractive index - Also known as the Index of Refraction, the ratio of the speed of light in a vacuum to the speed of light in a material.
Relay - A device that acts like a switch and is controlled by a current. The relay switch contacts and then controls another circuit to pass a signal. Most relays are either solid state or electromagnetic.
Remote control - A wired or wireless device for controlling the function of another device at a distance. Also see “IR remote.”
Repeater - See HDCP
Repeater/Regenerator - A repeater is a device that detects a weak signal and boosts its power for continued transmission. A regenerator receives a signal and regenerates or reconstructs its waveform for transmission.
Resistance - The opposition to the flow of electric current. See “Power” and “Ohm.”
Resistor - An electrical component that limits the flow of current via resistance or impedance. It allows a specific amount of current to flow, as determined by the voltage applied to the resistor.
Resolution - The density of lines or dots that make up an image. Resolution determines the detail and quality in the image. A measure of the ability of a camera or video system to reproduce detail, or the amount of detail that can be seen in an image. Resolution is often expressed as a number of pixels, but more correctly, it is the bandwidth. A sharp, clear picture has high resolution. Also see “Resolution (horizontal)” and “Resolution (vertical).”
Resolution (horizontal) - The amount of detail in a horizontal direction in a video image. It is expressed as the number of distinct vertical lines, alternately black and white, that can be seen in the width of the picture. This information is usually derived from observation of the vertical wedge of the test pattern. Horizontal resolution depends on the high requency amplitude and phase response of the pick-up equipment, as well as the transmission medium and the monitor itself.
Resolution (vertical) - The amount of resolvable detail in a vertical direction in a video image. It is expressed as the number of distinct horizontal lines, alternately black and white, that can be seen in a test pattern. Vertical resolution is primarily determined by the number of horizontal scanning lines in a frame.
Resonance - (1) Electronically, the condition where the inductive reactance and capacitive reactance are equal. (2) Acoustically, an intense and prolonged sound produced by a sympathetic vibration.
Retrace - During the scanning of a picture onto a screen, scan lines are produced from left to right. Before scanning the next line, the electron beam must get back to the left side of the screen. This is called retrace. The beam must be turned off (blanked) during retrace time. (See “Horizontal blanking” and “Vertical blanking.”) A retrace problem could appear as missing video information on the left side of the screen.
Retrace time - The time required to move the scanning beam from the right side to the left side of the screen.
Retro - A rear-projection video display.
Return loss - A measure of reflected energy in decibels at a specific frequency and cable length.
Reverberation - The persistence of sound in an enclosed space, as a result of multiple reflections after the sound source has stopped. The decaying residual signal that remains after a sound occurs, created by multiple reflections as the original sound wave bounces off walls, furniture, and other non-absorbing barriers within a room or other acoustical environment. A room with very little reverberation is called a “dead” room, which is the opposite of a “live” acoustic space which is very reflective.
Reverberation time - The length of time required for the sound field to collapse, after the sound source has stopped.
RF - Radio frequency. A range of frequencies used for electromagnetic transmission (e.g., radio and TV).
RF adapter - A device that allows video and audio signals from a video tape recorder (VTR) or computer to be shown on a standard TV receiver. This device produces comparatively poor resolution and picture quality. Also called “RF converter.”
RF control - A medium of remote control from which signals are sent to the controlled equipment via data pulses modulated on an RF carrier signal.
RFI - Radio Frequency Interference. High frequency interference from transmissions such as telephones, microwaves, and television stations.
RG/U - Radio Guide/Universal. Military abbreviation for coaxial cable.
RGB - Red, Green, and Blue. The chroma information in a video signal. The basic components of the color television system. They are also the primary colors of light in the additive color process. Also see “Subtractive color.”
RGBHV - Red, Green, Blue, Horizontal, and Vertical Sync. A five-wire signal where the red, green, and blue video signals, as well as the horizontal and vertical sync signals, are on its own conductor.
RGBS - The Red, Green, and Blue chroma information in a video signal, with a separate channel for the sync signal.
RGsB - Red, Green, Blue, and Sync on Green. A three-wire signal with separate red, green, and blue video signals with the sync (horizontal and vertical) on the green signal.
Ribbon cable - A cable with several copper wires or optical fibers, each jacketed side-by-side in a flat, ribbon-like structure.
Ribbon splice - The splicing of individual optical fibers of a ribbon cable, with each fiber spliced on a groove of a substrate or etched silicon chip. Each groove is spaced evenly and a flat cover holds the fibers in place on the substrate.
Ripcord - A cord of strong yarn, situated under the cable jacketing, used to facilitate in stripping and removal of the jacket.
Ripple - Generally referring to the wavelike variations in the amplitude response of a filter.
Rise time - The time required for a signal to go from 10% to 90% of its maximum amplitude level.
Riser - A type of cable designed for vertical runs in shafts spanning multiple floors in a building.
RJ - Registered Jack. A type of modular jack that is similar to those used with telephones. Examples: RJ-11 = 4 or 6 wire module, RJ-45 = 8-wire module.
RJ-45 - Registered Jack-45. A connector similar to a telephone connector that holds up to eight wires, used for connecting Ethernet devices.
RMS - An acronym for “root mean square.” Used in audio to help rate the continuous power output of an amplifier or input capability of speakers. This is the preferred method for comparing anything in audio applications.
ROM - Read Only Memory. Permanent memory that can only be loaded once, normally by the manufacturer. Contents may not be altered or removed. Also see “PROM”, “EPROM”, and “EEPROM.”
Room mode - An acoustical resonance in a room caused by parallel wall surfaces. Any set of parallel walls will establish a series of standing waves, the lowest one of which has the wall spacing as a half-wavelength. These sound waves interfere with one another to produce a series of places where the SPL is high and another series of places between then where the SPL is very low. It is as if the sound wave were stationary between the two surfaces.
Rooming - With large matrix switching systems, such as the Extron Matrix 3200/6400 Series Switchers, specific outputs can be assigned to a room. That room sees only those outputs, even though they are part of a total switching system. The outputs seen by a room have virtual numbers (may be different from the physical numbers). Room presets using those outputs can be saved and recalled without affecting other switcher outputs.
RS-170A - EIA technical standard for NTSC color TV. A video standard that ensures proper synchronization of video signals and components.
RS-232 - An Electronic Industries Association (EIA) serial digital interface standard specifying the characteristics of the communication path between two devices using either DB-9 or DB-25 connectors. This standard is used for relatively short-range communications and does not specify balanced control lines. RS-232 is a serial control standard with a set number of conductors, data rate, word length, and type of connector to be used. The standard specifies component connection standards with regard to the computer interface. It is also called RS-232-C, which is the third version of the RS-232 standard, and is functionally identical to the CCITT V.24 standard.
RS-330 - An EIA technical standard that provides details for industrial closed-circuit television (CCTV).
RS-343A - An EIA standard for high resolution monochrome CCTV.
RS-422 - An EIA serial digital interface standard that specifies the electrical characteristics of balanced (differential) voltage, digital interface circuits. This standard is usable over longer distances than RS-232. This signal governs the asynchronous transmission of computer data at speeds of up to 920,000 bits per second.
RS-485 - An EIA standard for multipoint communications. It is similar to RS-422, but can support several nodes per line because it uses lower impedance drivers and receivers and allows for addressing.
S/N ratio - See “Signal-to-Noise ratio.”
S/PDIF - Sony/Philips Digital Interface. A standard audio file transfer format, S/PDIF allows the transfer of digital audio signals from one device to another without it first having to be converted to an analog format.
S/PDIF – Sony/Philips Digital Interconnect Format - A data protocol for compressed or uncompressed digital audio co-developed by Sony and Philips Electronics and now part of the larger AES/EBU audio standard. S/PDIF is often misconstrued as a connection type; however, S/PDIF audio can be found in products using either a 75 ohm coaxial connection or a TOSLINK fiber optic connection. S/PDIF is commonly found in Compact Disc and DVD players.
SACD – Super Audio Compact Disc - A very high fidelity, read-only optical disc format for both two-channel stereo and 5.0 (no sub-woofer) or 5.1 surround sound audio. SACD can store up to 10 times as much data as a standard audio CD, up to 7.95 GB. Support for SACD audio was added to the HDMI 1.2 specification in 2005.
Sag - A measure of the amount of sag in a fiber optic cable, taken at the midpoint of a span of cable between two points of support.
Sag section - A section defining a span of fiber optic cable between two points of support.
Sag span - A span selected within a sag section, used as a control to determine the proper sag, and therefore, tension of a fiber optic cable. At least two, and normally three sag spans in a sag section are required to sag a section properly.
Sag tension - The tension at which a fiber optic cable is designed to be installed.
Sample rate - The rate at which an analog signal is sampled. It is frequently expressed as kilosamples/sec (kS/s) or Megasamples/sec (MS/s. For example, 44.1 kHz is the standard sample rate for compact disks; 48 kHz is often used with digital audio tape (DAT) recording. A higher sample rate allows a higher frequency response. In order to accurately reconstruct a sound, the sample rate must be at least twice the highest frequency in the sound.
SAP - Second Audio Program. A feature of MTS television stereo audio, SAP permits the delivery of a second soundtrack for enhanced services such as second language or descriptive video services (DVS) for the vision impaired.
Saturation - Chroma, chroma gain. The intensity of the color, or the extent to which a given color in any image is free from white. The less white in a color, the truer the color or the greater its saturation. On a display device, the color control adjusts the saturation. Not to be confused with the brightness, saturation is the amount of pigment in a color, and not the intensity. Low saturation is like adding white to the color. For example, a low-saturated red looks pink.
SC - Subcarrier. The modulation sidebands of the color subcarrier containing the R-Y and BY information. A secondary signal containing additional information that is added to a main signal.
SC/H phase - Subcarrier to Horizontal phase. In NTSC video, this is the phase relationship of the subcarrier to the leading edge of horizontal sync. SC/H phase is correct when the zero crossing of subcarrier is aligned with the 50% point of the leading edge of sync. In PAL video, the SC/H phase is defined as the phase of the EU component of the color burst extrapolated to the half amplitude point of the leading edge of the synchronizing pulse of line 1 of field 1.
Scaler - A device that takes a standard video signal, decodes it, and uses advanced digital signal processing technology to scale the image to the optimal or native resolution of a display device. (Usually at a higher rate).
Scaling - Scaling is changing the size of an image to fit the native rate (or pixel size) of a display device, without changing its shape. For example, to fit a 720x480 resolution TV image on a 1024x768 XGA resolution display, the TV image has to be scaled “up”; pixels need to be created in order for the original image to fill the screen. Alternately, to fit a 1280x1024 SXGA resolution image on an XGA resolution screen, the image will need to be scaled “down”; pixels need to be removed from the original image in order for it to fit on the screen. There are many different methods for image scaling, and some produce better results than others.
Scan - (1) In video, to move an electron beam across the raster in a camera or monitor. (2) To feed visual information into a computer by means of an optical device called a scanner.
Scan converter - Also called “video converter” or “TV converter,” a scan converter is a device that changes the scan rate of a source video signal to fit the needs of a display device. Examples: computer-video to NTSC (TV), or NTSC to computer-video.
Scan doubler - A device used to change composite interlaced video to non-interlaced component video, thereby increasing brightness and picture quality. Also called “line doubler.”
Scan-doubling - The process of making the scan lines less visible by doubling the number of lines and filling in the blank spaces. Also called “line-doubling.”
Scattering - A source of optical signal loss in a fiber optic system, caused by the scattering of light due to small particles and other imperfections in the fiber.
Scribe - Scratching the surface of the fiber so that it can be precisely and cleanly cut at a right angle to the fiber axis.
Scribe tool - A device consisting of a scribing blade, usually made from diamond or tungsten carbide, used to scribe, or score a fiber to allow for a clean break and a smooth endface.
Scrolling - The displayed image (or interfering noise on the image) rolling constantly on the screen.
SCSI - Small Computer System Interface. Pronounced “skuzzy.” An industry-standard input/output bus for peripheral computer devices, such as hard disks and CD-ROM drives. A standard peripheral bus on Mac computers. Improvements, such as the number of data lines and speed, have been made to the original SCSI to become SCSI-2 and SCSI-3.
SDI - Serial Digital Interface. The standard based on a 270 Mbps transfer rate. This is a 10bit, scrambled, polarity independent interface with common scrambling for both component ITU-R 601 and composite digital video and four channels of (embedded) digital audio.
SDTV - Standard digital television. A serial digital format whose samples and timing are derived from 4:2:2 digital component video sources. The main difference between existing digital component video and SDTV is an MPEG-2 compression step to reduce the channel bandwidth.
Seamless switching - A feature found on many Extron video switchers. This feature causes the switcher to wait until the vertical interval to switch. This avoids a glitch (temporary scrambling) which normally is seen when switching between sources.
SECAM - Sequential Couleur Avec M?moire, or “sequential color with memory.” A composite color transmission system that potentially eliminates a need for both a color and hue control on the monitor. One of the color difference signals is transmitted on one line and the second is transmitted on the second line. Memory is required to obtain both color difference signals for color decoding. This system is used in France, North Africa, Russia, Saudi Arabia, and many Eastern European countries. It is similar to PAL but produces color signals in a different manner. SECAM uses 625 horizontal scan lines, 50 fields per second (625/50).
SED - Surface-conduction Electron-emitter Display. SED is a new type of flat-panel display technology developed by Canon and Toshiba. SED is capable of high levels of brightness and color performance, as well as a wide angle of visibility, that on a par with a CRT. Large screens can be produced by simply increasing the number of electron emitters in accordance with the required number of pixels.
Sensitivity - A standard way to rate audio devices like microphones, loudspeakers, and amplifiers. For loudspeakers, sensitivity is rated by applying 1 watt of power to the speaker and measuring sound pressure level (SPL) at one meter. For microphones, sensitivity is expressed as the minimum input signal required to produce a standard output level. For a power amplifier, sensitivity is rated as the input level required to produce 1 watt of power output into a specified load impedance, typically 4 ohms or 8 ohms.
Serial data - A way to transfer information by breaking the characters of a word into bits, which are then transmitted sequentially along a single line. Compare to parallel, which uses more than one line.
Serial port - An input/output connection on the computer that allows it to communicate with other devices in a serial fashion data bits flowing on a single pair of wires. The serial port is used with RS-232 protocol.
Serration pulse - A vertical synchronizing pulse divided into a number of small pulses, each acting for the duration of half a line in a television system. Serration pulses are used to keep the horizontal oscillator synchronized during the vertical sync pulse interval.
Service loop - A deliberately allotted slack of fiber optic cable, in a splice tray, closure, vault, or communications output, to accommodate future needs.
Shadow mask - A metal plate with holes or vertical lines that is used to determine exactly where the electron beam strikes the CRT screen.
Sharpness - The definition of the edges of an image. Also see “Peaking.”
Sharpness control - Same as Peaking control.
Sheath - Also known as a cable jacket, the outer protective covering of wire or fiber optic cable.
ShiftLock™ - An Extron feature used to lock video displays together when using Extron VideoShift™, synchronizing the movement of their images.
Signal loss - A video problem that shows up as a faint picture for lack of video information.
Signal to Noise ratio – SNR - Also stated as “S/N ratio”. The ratio is expressed in decibels as a ratio between the audio or video signal level and that of the noise accompanying the signal. The higher the S/N ratio, the better the quality of the sound or picture.
Simplex cable - A cable comprising a single optical fiber.
Single-ended - An unbalanced circuit where one side of the circuit or transmission line is grounded. Single-ended audio is unbalanced audio.
Single-Link DVI - The electrical signaling used to transmit data over DVI is known as transition minimized differential signaling, or TMDS. A single TMDS link carries three data channels and one clock signal, with a maximum video frequency of 165MHz, capable of standard resolutions up to 1920x 1200 pixels. See also “Dual-Link DVI.”
Single-Link HD-SDI - See “SMPTE 292M.”
Single-mode Fiber – SMF - An optical fiber with a small core, through which only a single mode can propagate.
Sink - See HDCP
SIS™ Simple Instruction Set.™ - A set of commands developed by Extron that allows easy RS232 control of certain Extron products with a minimal number of characters in the commands and responses.
Skew - Refers to the timing difference which occurs when electrical signals which are traveling over different pairs of cables reach their destinations at different times. The different arrival times of the signals may present a problem when simultaneous arrival with no delay is required.
Skew-Free - A reference to special twisted pair cable in which the length differences between cables reduced to a minimum, thus reducing cable skew.
SL - The Extron product designation for ShiftLock.
Slew rate - The ability of audio equipment to reproduce fast changes in amplitude. Measured in volts per microsecond, this specification is most commonly associated with amplifiers, but applies to most types of audio products. In amplifiers, a low slew rate “softens” the attack of a signal, “smearing” the transients and sounding “mushy.” Since high frequencies change in amplitude the fastest, this is where slew rate is most critical. An amp with a higher slew rate will sound “tighter” and more dynamic.
Smearing - A video problem where objects such as horizontal bars extend past their boundaries. Also called “over-peaking.”
SMPTE - Society of Motion Picture and Television Engineers. A global organization, based in the United States, that sets standards for baseband visual communications. This includes film as well as video and television standards.
SMPTE 259M - Defines the SDI serial digital interface common to most standard definition digital video products. SMPTE 259M includes several data rates, including 143 Mbps (NTSC composite digital), 177 Mbps (PAL composite digital), 270 Mpbs (4:2:2 component digital, 4:3 standard video aspect), and 360 Mbps (4:2:2 component digital, 16:9 widescreen video aspect). Of the group, 270 Mbps and 360 Mbps are the most common data rates.
SMPTE 292M - Defines the HD-SDI high definition serial digital interface. SMPTE 292M has data rate of 1.485 Gbps for 4:2:2 component digital in 16:9 widescreen video aspect. Full bandwidth HD-SDI can be transmitted 300 feet (100 m) on standard RG6 coaxial cable, and more than 60 miles (100 km) using fiber optic technology. SMTPTE 292M is considered a single link HD-SDI signal, in that only one coaxial cable is required to transmit the data.
SMPTE 310 - A broadcast standard for transmitting one or more DTV – digital television channels, and ancillary content, as part of a single data stream.
SMPTE 372M - Defines a full bandwidth, 4:4:4 RGB color space and bandwidth up to 2.97 Gbps on two coaxial cables, often referred to as “dual-link HD-SDI. SMPTE 372M is most commonly associated with dual-link HD-SDI, wherein two coaxial cables are used to carry alternate pixels, thus doubling the data rate and available resolution. Dual-link HD-SDI is sufficient for 1080/60p and 1080/24Psf video streams; however, the “Super2k” format used in digital cinema, 2048x1080, progressive scan, 4:4:4 RGB color space, is the highest data rate possible with one dual-link HD-SDI connection.
SMPTE 424M - Defines a full bandwidth, 4:4:4 RGB color space and bandwidth up to 2.97 Gbps on a single coaxial cable. SMPTE 424M is colloquially known as 3G-SDI, a term used to describe 2.970 Gigabit per second digital video over a single-link coaxial cable. 3GSDI is capable of supporting HDTV 1080p video at 50 or 60 frames per second. Most 3G-SDI terminal equipment, such as Extron 3G-SDI matrix switchers, simple switchers, distribution amplifiers, cable equalizers, and fiber optic extenders, is capable of supporting standard SDI data rates from 270 Mbps to 2.970 Gbps.
SMPTE pattern - The video test pattern consisting of color, black, and white bands used as a standard for setting up video equipment.
SMTP - Simple Mail Transfer Protocol. Internet standard for e-mail exchange across systems/networks on the Internet.
SNMP - Simple Network Management Protocol. Allows for management of network devices with administration software.
Snow - Visual noise in a video picture giving the appearance of white flecks of snow.
Software - The programs used to instruct a processor and its peripheral equipment to perform prescribed operations.
SOG - Sync On Green. The combined horizontal and vertical sync signals are integrated with the green video signal.
Sound level meter - An instrument designed to measure sound pressure level.
Source - See HDCP
Source - The optical source in a fiber optic system, usually an LED or laser diode.
Spatial resolution - Spatial resolution is a measurement of the total number of pixels displayed in an entire image, usually noted in terms of horizontal by vertical (640 x 480).
Speaker (conical) coverage - Ceiling speakers, much like a spot light, generally project audio in a conical coverage pattern. As with any device featuring a conical coverage pattern, the higher it’s mounted, the larger the circle of coverage. As the area of coverage increases, audio amplification wattage must also increase to maintain the same sound pressure level per unit of area of coverage.
Speaker polarity - Loudspeakers of all types have a positive and a negative polarity. A speaker cone that moves forward (out) when a positive voltage is applied is said to have “positive polarity”; conversely, a speaker cone that moves backward (in) when a negative voltage is applied is said to have “negative polarity.” Speakers must be wired in such a way to ensure that they are “in phase”, that is, all speaker cones are moving in the same direction, in or out, at the same time. Audio test generators, such as the Extron VTG 300 and VTG 400, include a test tone (typically a “click” or “pop”) that’s used to check speaker polarity
Spectrum analyzer - An device used to measure and analyze the frequency spectrum of an input signal, usually amplitude (vertical) vs. frequency (horizontal).
Speed of light - 2.998 x 10e8 meters per second in free space.
Splice - A permanent connection between the ends of two optical fibers by mechanically joining them together, or heating to fuse them together.
Splice closure - A housing designed to protect splices in a optical fiber from damage, sealing them from the external environment.
Splice organizer - A device that facilitates the splicing of optical fibers, as well as their permanent storage.
Splice panel - A rack or wall-mounted panel that allows fiber optic cables to be organized and spliced. The panel holds splice trays, cable routing, and slack storage.
Splice protector - In fiber optics, a device used to provide protection and mechanical strength to a fusion splice, so that it can be handled and organized into a splice tray or other storage.
Splice tray - A container that is used to secure, organize, and protect individual spliced optical fibers.
Split screen - A video effect where portions of images from two sources divide the screen.
Stapler cleaver - A fiber optic cleaver that is shaped similar to a stapler.
Static IP - An IP address that has been specifically (instead of dynamically see “DHCP”) assigned to a device or system in a network configuration. This type of address requires manual configuration of the actual network device or system and can only be changed manually or by enabling DHCP.
Static mesh - A basic de-interlacing process used in scalers for video content that contains no movement. This type of processing results in a sharp image with crisp details but will cause images to tear when motion occurs.
Step index fiber - A fiber in which the refractive index is uniform throughout the core. On the other hand, for a graded index fiber, the refractive index of the core varies radially between the fiber axis and the cladding.
Stereo - A process of using separate audio signals on separate channels for the left and right audio, thereby giving depth, or dimension to the sound.
Straight Tip – ST - A fiber optic cleaver that is shaped similar to a stapler.
Stripper - A tool used to remove the jacket that surrounds a cable or an individual wire within the cable. In fiber optics, a stripper is used to remove the buffer coating from an optical fiber.
Subnet mask - The method used for splitting IP networks into a series of subgroups or subnets. The mask is a binary pattern that is matched up with the IP address to turn part of the host ID address field into a field for subnets.
Subscriber Connector – SC - A popular fiber optic connector that features a snap (push-pull) coupling type. Being replaced by the LC in most applications.
Subwoofer - A loudspeaker designed to reproduce only the very low end of the audio frequency range, typically one or two octaves between 20 Hz and 80 to 100 Hz.
Summing amplifier - A device which combines the left and right channel audio signals into a single mono channel. It is useful in multi-speaker mono paging systems, or in large stadium and church environments.
Super Physical Contact – SPC - In fiber optics, a specific endface polish for a connector to achieve typically a -50 dB return loss in single-mode applications.
Superimposition - Placing one image over another so that both may be seen at the same time. The effect can be achieved in many ways: by more than one exposure on a single piece of film, by multiple printing, or by registered projection. Abbreviated “super.”
SVGA - Super Video Graphics Array. A term used to denote resolutions higher than VGA (640 x 480). SVGA computer graphics cards have a resolution of 800 x 600 (480,000 pixels) but may be able to output resolutions of up to 1280 x 1024 and 16 million colors.
S-VHS - Super-Video Home System. A high band video recording process for VHS that increases the picture quality and resolution capability. Also see “S-video.”
S-video - A composite video signal separated into the luma (“Y” is for luma, or black and white information; brightness) and the chroma (“C” is an abbreviation for chroma, or color information).
Sweep - In audio, a sequence of puretone frequencies used to generate a frequency response curve.
Switcher - (1) A device that allows a selection between more than one source, such as video cameras, VCRs, etc. In audio/video, switchers are a means of connecting an input source to an output device or a system. Also see “Matrix switcher.” (2) A term often used to describe a special effects generator; a unit that allows the operator to switch between video camera signals. Switchers are often used in industrial or security applications to switch between video cameras that view certain areas for display on a monitor, or system of display devices. These kinds of switchers do not have sync generators.
SXGA - Super Extended Graphics Array. A graphics standard with a resolution of 1280x1024 (1,310,720 pixels), with an aspect ratio of 5:4. This exceeds XGA (1024 x 768, at 786,432 pixels).
SXGA+ - Introduced in 2004, a graphics standard with a resolution of 1400x1050 (1,470,000 pixels) with an aspect ratio of 4:3.
SxRD Silicon xTal Reflective Display - A reflective liquid crystal display technology from Sony that’s capable of very high resolutions and a very high contrast ratio. SxRD equipped projectors are capable of resolutions up to 4096 x 2160 pixels, or four times the resolution of HDTV (1920x1080).
Sync - Synchronization. In video, sync is a means of controlling the timing of an event with respect to other events. This is accomplished with timing pulses to insure that each step in a process occurs at the correct time. For example, horizontal sync determines exactly when to begin each horizontal scan line. Vertical sync determines when the image is to be refreshed to start a new field or frame. There are many other types of sync in a video system. (Also known as “sync signal” or “sync pulse.”)
Sync generator - A circuit that produces sync impulses used to control the time when certain events happen electronically. Also known as a “synchronizing pulse generator.”
Sync polarity - (1) A circuit can be designed to operate on the positive-going or negative-going part of the sync pulse. Some equipment has a sync polarity option switch to allow selecting which edge (plus or minus) to trigger on. (2) This refers to the duty cycle of the sync signal. A positive polarity sync signal is low most of the time, and high for a short time. Negative polarity sync is high most of the time and low for a short time.
Sync termination adapter - See “ASTA.”
System switcher - An A/V switching device that also communicates with other components in a system including room lights and motorized devices. For instance, in addition to controlling a projector, a system switcher can turn lights on and off and raise and lower a motorized projector screen. CCITT standard for digital computer data interchange videoconferencing.
Tap - A fiber optic coupler with two outputs, the second of which, part of the incoming light is tapped off into another fiber.
TCP - Transmission Control Protocol. A method (protocol) used along with the Internet Protocol to send data in the form of message units between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the individual units of data (called a packet) that a message is divided into for efficient routing through the Internet.
TCP/IP - Transmission Control Protocol/Internet Protocol. The communication protocol of the Internet. Computers and devices with direct access to the Internet are provided with a copy of the TCP/IP program to allow them to send and receive information in an understandable form.
Tee coupler - A T-shaped fiber optic coupler with one input and two outputs.
Telecommunications - An electronic method of transmitting information from one location to another over a telephone network.
Telecommunications closet - An enclosed, secure space for housing telecommunications equipment, cable terminations, and cross connects.
Teleconferencing - A meeting between people at two or more locations who can communicate by audio and/or visual devices often via telephone and/or closed-circuit television. Also see “Videoconferencing.”
Telnet - A computer network utility available on most PCs that allows the computer system to communicate with one of its remote users or clients. A user who wishes to access a remote system initiates a Telnet session using the address of the remote client. The user may be prompted to provide a user name and password if the client is set up to require them.
Temporal - Relating to the sequence of time or to a particular time.
Terminal - A device typically having a keyboard and display that is capable of sending text to and receiving text from another device, a network, etc.
Termination - 1. A load or impedance at the end of a cable or signal line used to match the impedance of the equipment that generated the signal. The impedance absorbs signal energy to prevent signal reflections from going back toward the source. For video signals, termination impedance is typically 75 ohms; for sync signals, it is usually 510 ohms. 2. A connector at the end of a cable.
Termination Tools - Tools used in the preparation and installation of connectors on cables or optical fibers.
Terminator - A device that provides termination for a signal line or several signal lines at the end of a cable. Usually a close-tolerance resistor for each signal, a terminator is often mounted in its own enclosed connector, making it easy to install. In fiber optics, an optical plug used to fully terminate the optical path so no light is reflected back toward the source.
TFT - Thin Film Transistor LCD panel. A type of LCD flat panel display screen in which each pixel is controlled by one to four transistors. The TFT technology provides the best resolution of all the flat panel techniques, but it is also the most expensive. TFT screens are sometimes called active matrix LCDs.
THD - Total Harmonic Distortion. The amount of internally generated noise in a receiver that varies from the ideal sound wave. Since the perfect audio wave is physically impossible, the variation from the ideal wave is the percentage referred to as THD.
THD+N - Total Harmonic Distortion plus Noise. THD+n is a specification that includes both harmonic distortion of the sine wave and non-harmonic noise. THD+N tells the user what amount of hum, noise, and interference has been added to the audio signal by the equipment through which it is passing.
Third octave - A term that refers to frequencies spaced three octaves apart. For example, the third-octave above 1 kHz is 8 kHz. Third-octave filters, typically in a bank between 20 Hz and 20 kHz, are useful because they have a good correlation to the subjective response of the human ear. Filtering broad spectrum pink noise through a third-octave filter is often used to characterize acoustical systems, such as loudspeakers, or for the measurement of absorption or damping of acoustical materials. See “Fletcher-Munson Curve.”
THX - Originally part of Lucasfilm, Ltd., THX embodies a series of certification programs for equipment, software, production environments, and presentation venues with the objective of delivering optimum sound and video.
Tight buffered cable - A fiber optic cable for indoor use in which the buffer coating tightly surrounds the cladding for extra protection and provides color-coded identification.
Time base corrector - Video tape recorder (VTR) playback circuitry used to smooth out the wavering edges of a video image.
Time base error - Slight errors in the line-to-line position of video information that occur between recording and playback. At the time of playback, these appear as serrations, tending to make the edges of the image waver.
Time base generator - A sync generator which puts a clock signal on the videotape to refer to for precise horizontal lock-up of an image.
Time code - A digital or binary code used to label each frame of a video signal. This is very useful for editing the video since the time code is in the form of hours, minutes, seconds, and frames.
Time division multiplexing - TDM - A digital transmission scheme where the channel is divided into two or more time slots or subchannels, such that the subchannels are taking turns in the bit stream. Multiple digital signals are multiplexed into a serial digital stream. The serial digital stream is transmitted to the receiver where it is de-multiplexed into the individual digital signals.
Time domain - A means of representing a signal on a graph of amplitude (usually on the vertical axis) versus time (usually on the horizontal axis). An oscilloscope produces a time domain representation of a signal. See “Frequency Domain.”
Tint - A relative measure of the amount of white in a given color. Also see “Hue.”
TMDS - Transition Minimized Differential Signaling. An all-digital video transmission standard developed by Silicon Image, Inc. TMDS is the core technology used in DVI (Digital Visual Interface) and HDMI (High Definition Multi-media Interface.) As implemented in DVI, the TMDS standard is limited to 5 meters or 15 feet. There are no such cable length limitations specified for HDMI. Silicon Image markets this standard as PanelLink®.
Toggle - To switch between alternate states. For example, between on and off, or caps and lower case.
Toggle switch - A switch having two positions or two states. When an activating force is applied, the state changes.
Toneburst - A group of short duration audio frequencies, from 20 Hz to 20 kHz, used to evaluate the behavior of a listening environment in response to loudspeakers. Toneburst is used to identify room reflections caused by resonance or standing waves. See “Room Mode.”
TOSLINK - An optical fiber connection standard for digital audio developed by Toshiba. TOSLINK is very commonly used for audio output from Compact Disc and DVD players, as well as some game consoles. A generic name, “EIAJ optical,” is sometimes used to describe this standard.
Total internal reflection - The total reflection of light as it reaches a boundary between two optical media at an angle of incidence greater than the critical angle.
Touch panel - A control panel with a flat surface (usually with graphic divisions or buttons) that functions as a switch or control. Also called a “touch screen.”
TP - Twisted Pair. Cable that uses small twisted pairs of wires in a common jacket/sheath to transmit and receive network or telephone signals; can be either shielded (STP) or unshielded (UTP). The Extron product family includes twisted pair transmitters, twisted pair receivers, and twisted pair cabling.
Transceiver - A device that can operate as a transmitter, receiver, or both.
Transcoder - An electronic device designed to convert one signal type to another, and vice-versa. For example, the Extron YCS Transcoder both decodes composite video into S-video, and encodes S-video into composite video.
Transducer - In audio, a device to convert sound to electrical energy or vice versa. Microphones and loudspeakers are two type of transducers. Microphones convert sound into electrical energy; loudspeakers convert electrical energy back into sound.
Transformer taps - A transformer is a simple device that “transforms” electricity from one voltage to another. Transformers are added to conventional, 8 ohm loudspeakers to adapt them for use in constant voltage, multi-speaker distributed audio systems. The transformers are “tapped”, that is, designed with several different output points, to allow for different output wattages from the 70 V or 100 V constant voltage input. Taps are typically spaced at 2x increments, for example, 2 watts, 4 watts, 8 watts, 16 watts, etc.
Transistor - An electronic component that acts as a valve, or switch, allowing one signal (voltage or current) to control another.
Transmit – Tx - In fiber optics, to send an optical signal down a fiber optic cable using a light source, such as an LED or laser. The transmit port of a transceiver.
Transmitter - A device that converts from one signal type to another for transmission. In fiber optics, the component or subsystem that converts an electrical signal to an optical signal and launches the optical signal down a fiber optic cable using a light source, such as an LED or laser.
Trigger - A signal, typically TTL level, that is transmitted in order to synchronize two or more instruments.
Tri-level sync - A sync level scheme developed for HDTV in which the sync line first goes low, then transitions high while going through the reference voltage level, and then drops back down to the reference voltage. The transition of the positive-going sync signal through the reference voltage is the sync trigger.
Triple-Action Switching™ - A process in which the RGB signal is muted during the switching, until the projector has time to sync up to the new image. This way, when a switch is made, viewers don’t see the image scrambling that occurs until the projector syncs up. Instead, they see the image go blank and then the new image appears already synced up. This provides a professional appearance for presentations.
TTL - Transistor-to-Transistor Logic. A digital signal, usually 4-5 volts peak-to-peak with a distance limitation is 6-10 feet (1.8-3.0 meters). Signal splitting is acceptable. TTL signals are either on or off, and are characteristic of low resolution computers (CGA/EGA).
Tunable Laser - A laser in which its central wavelength can be varied or optimized as desired for a particular application.
TVL - TV line. A resolution specifying the amount of black and white alternating lines that can be displayed in horizontal or vertical directions. It can be applied to both continuous media video devices (B/W CRT, three-gun CRT projector) and fixed pixel video devices (LCD, DLP, plasma). It’s generally different from the pixel counts of a fixed pixel video device. See “Kell factor.”
Tweak - To adjust or fine-tune.
Tweeker - A small screwdriver for making sensitive adjustments to audio/visual and other electronic equipment. An Extron specialty.
Tweeter - A loudspeaker designed to reproduce high-pitched or treble sounds in the range of 4Hz to 20 kHz.
UHF - Ultra High Frequency. A television broadcast frequency range between 300 and 3000 MHz on channels 14 through 83. Also the name for a type of connector used for video cables.
UL® - Underwriters Laboratories. When marked by the UL symbol, a product has been tested and evaluated according to nationally recognized safety standards with regard to fire, electric shock, and related safety hazards. There is also a UL for Canada, sometimes called CUL, and a UL recognized component with its own symbol, resembling a backward “UR.”
Ultra Physical Contact – UPC - In fiber optics, a specific endface polish for a connector to achieve typically a -60 dB return loss in single-mode applications.
Unbalanced audio - An audio output where one of the two output terminals is at ground potential.
Underfilled Launch Condition – ULC - In fiber optics, a condition where the incoming light only fills a small percentage of the fiber core.
Underscan - A decreasing of the raster size (H and V) so that all four edges of the picture are visible on the screen. Underscanning allows viewing of skew and tracking that would not be visible in normal (overscanned) mode. It is also helpful when aligning test charts to be certain they touch all four corners of the raster. Likewise, when checking the alignment of multiplexer images from a film chain, underscan allows proper framing of the projected image going into the video camera.
UPS - Uninterruptible Power Supply. A power supply that continues to provide voltage for a limited time after the main power is off (fails).
URL - Uniform Resource Locator. This is the address that lets a resource on the internet be identified, located, and accessed
USB - Universal Serial Bus. USB was developed by seven PC and telecom industry leaders (Compaq, DEC, IBM, Intel, Microsoft, NEC, and Northern Telecom). The goal was easy plug-and-play expansion outside the box, requiring no additional circuit cards. Up to 127 external computer devices may be added through a USB hub, which may be conveniently located in a keyboard or monitor. USB devices can be attached or detached without removing computer power. The number of devices being designed for USB continues to grow, from keyboards, mice, and printers to scanners, digital cameras, and ZIP drives.
USB 1.1 - Universal Serial Bus 1.1. An external bus standard that supports data transfer rates of 12Mbps and 1.5Mpbs. A single USB port can connect up to 127 peripheral devices. See “USB 2.0.”
USB 2.0 - Universal Serial Bus 2.0. An external bus standard that supports data transfer rates up to 480Mbps, 12Mpbs, and 1.5Mpbs. USB 2.0 is an extension of USB 1.1 and is backward compatible with USB 1.1, using the same cables and connectors. See “USB 1.1.”
UV - Ultraviolet. Light/heat rays that have a shorter wavelength (and higher frequency) than those in the visible spectrum. UV rays are ordinarily filtered or blocked to prevent eye damage and dye fading.
UXGA - Ultra Extended Graphic Array. 1600 x 1200. A UXGA display has 1600 horizontal pixels and 1200 vertical pixels giving a total display resolution of 1,920,000 individual pixels that are used to compose the image delivered by a projector.
V - (1) Vertical (as in RGBHV), or the vertical sync connector on a panel. This is used when the sync is separated into horizontal and vertical components. (2) In electrical specifications, “V” is the abbreviation for volts.
VAR - Value Added Reseller. A party who purchases a product, adds something to it, such as hardware or software, and then sells it as a package.
Variable level control - This is a variable voltage level control similar to a contrast control on a data monitor. The level control increases or decreases the levels of red, green, and blue simultaneously, thus not affecting the adjusted grayscale of the monitor or projector.
Vault - A storage product that houses fiber optic cable slack and splice trays.
VCA - Voltage Control Amplifier. An amplifier whose output is controlled by varying its voltage rather than by direct resistance (as with a potentiometer). VCA’s are typically used in audio mixers; instead of the signal being directly manipulated by the fader (and being subject to inconsistencies in the fader itself), the fader controls a voltage that corresponds to a certain sound level.
VCO - Voltage Control Oscillator. Voltage-controlled oscillators are commonly found in wireless systems, frequency synthesizers, and other devices that must be able to tune across a band of frequencies.
VCR - Generally defined as Video Cassette Recorder. In Europe, however, VCR is a trademark for a particular video format developed by Philips.
VCSEL - Vertical Cavity Surface Emission Laser. A high speed, low cost laser diode that emits perpendicular to the surface of the chip, rather than from an edge.
Vectorscope - A special oscilloscope used in video systems to measure chroma.
VersaTools® - Extron product family of compact, affordable, and versatile solutions for common A/V system applications.
Vertical blanking - Turning off the electron beam in a CRT during the time the beam returns from the bottom of the screen to the top after scanning each field of a picture. If vertical blanking does not occur, a diagonal retrace line will display from the lower right to the upper left of the screen. Also see “Retrace.”
Vertical blanking interval - The blanking time at the beginning of each field. It contains equalizing pulses and vertical
Vertical centering control - Adjusting the vertical centering control one way shifts the displayed image toward the bottom of the screen and the other way shifts the displayed image to the top of the screen. Also called “vertical shift,” or “vertical position.”
Vertical double images - A video problem in which the display is split across the middle with two identical (squeezed) images on the top and bottom of the screen.
Vertical filtering - This is a feature in some Extron scan converters that controls the number of lines to process, and the way they are processed. This affects the sharpness vs. flicker of the scan-converted picture.
Vertical interval - The period of time between the end of one video field and the beginning of the next. During this time, the electron beam in a camera, monitor, or projector is turned off (blanked) while it returns from the bottom of the screen to the top. The portion of the video signal that represents this time period may also be called the vertical interval.
Vertical resolution - Also known as “vertical definition.” The number of distinct horizontal lines, alternately black and white, that can be seen in a TV image. Vertical resolution is fixed by the number of horizontal lines used in scanning.
Vertical temporal - A scaling process for video content that contains movement. This type of scaling process employs an averaging technique to merge the odd and even fields of video into a single frame. This type of processing treats the entire picture as if in motion and results in less motion artifacts. Disadvantages include blurring and loss of vertical resolution.
VESA - Video Electronics Standards Association. A nonprofit member organization dedicated to facilitating and promoting personal computer graphics through improved standards for the benefit of the end-user. www.vesa.org
VGA - Video Graphics Array. Introduced by IBM in 1987, VGA is an analog signal with TTL level separate horizontal and vertical sync. The video outputs to a 15-pin HD connector and has a horizontal scan frequency of 31.5 kHz and vertical frequency of 70 Hz (Mode 1, 2) and 60 Hz (Mode 3). The signal is non-interlaced in modes 1, 2, and 3 and interlaced when using the 8514/A card (35.5 kHz, 86 Hz) in mode 4. It has a pixel by line resolution of 640 x 480 with a color palette of 16 bits and 256,000 colors.
VHF - Very High Frequency. Television broadcast range between 30 and 300 MHz, on channels 2 through 13. The FM radio band is between channels 6 and 7 (88 to 108 MHz).
VHS - Video Home System. The half-inch videocassette format originated and developed by JVC and adopted by a number of different manufacturers.
Video - Of or pertaining to the visual component of a television signal. For computers, video refers to the rendering of text and graphics images on a display device.
Video amplifier - A low-pass amplifier with a bandwidth of 2 to 10 MHz, used to strengthen the video signal for TV transmission and reception.
Video connector - The connector on the video card or computer’s graphics output that is connected to the video input on the local monitor.
Video projector - A device that projects a video image onto a presentation surface.
Video standards - See “NTSC”, “PAL”, and “SECAM.”
Videoconferencing - Conducting a live conference between two or more locations using video cameras, microphones, and video monitors. The participants can be seen as well as heard. Referred to as a virtual conference room. Also see “Teleconferencing.”
Video-follow-audio - In videoconferencing, when the video source switches automatically to show the person speaking, regardless of the location.
Virtual map - Used with the Extron virtualized matrix switchers (Matrix 3200/6400/12800 Series), a virtual map is made of tables stored in memory that relate physical connectors (on the back panel) to logical connections (as seen by the user). In printed form, this can show physical input/output connector numbers as they relate to virtual input/output numbers.
Virtual memory - The process of increasing the apparent size of a computer’s random-access memory (RAM) by using a section of the hard disk storage as an extension of RAM.
Virtual switching - A means of making real, physical input or output ports appear to have different numbers. For example, the Extron Matrix 6400 Switcher can be programmed to switch a set (group) of connectors as one. Also see “Virtual map.”
Visible Light - The region of the electromagnetic spectrum that is visible to the human eye, from 380 to 770 nm.
VITC - Vertical Interval Time Code. Timecode information that is stored on specific scan lines during the vertical blanking interval.
VLB - Video Loopback. A feature in some switchers that allows a video signal to exit to another device, such as a decoder or scaler, and the output of that device is then used as another input to the same switcher. This allows any switcher input to use the decoder or scaler, saving the cost of buying separate units.
Volt - The electrical potential difference or electromotive force that will cause current of 1 ampere to flow through the resistance of 1 ohm. Symbolized by “V.”
Voltage - The electrical potential difference or electromotive force expressed in volts. Also see “Volt.”
VS - VideoShift™. A technique used to move a video image around on the screen to prevent burn-in, or destruction of the phosphor. For example, burn-in can occur on flight schedule monitors in airport terminals, where the same image stays on the screen for a long period of time.
VTG - Video Test Generator. An Extron device that generates video test patterns at scan rates that simulate the most popular applications.
VU - Volume Unit. A unit that is designed to measure perceived loudness changes in audio. 100 VU is 100 percent of the audio that is supposed to be present. VU is measured on a VU meter.
VU meter - Volume Unit meter. For audio systems or recorders, a VU meter is a device that indicates the relative levels of the audio being recorded or played. It is usually calibrated to show a maximum recording level to avoid tape saturation and distortion
WAN - Wide Area Network. Long-distance networks using various transmission technologies such as the Internet, frame relay/ATM, fiber, or ISDN.
Watt - A unit of electrical power used to indicate the rate of energy produced or consumed by an electrical device. One watt is one joule of energy per second. Also see “Power.”
Waveform - A display of a signal (on an oscilloscope) that shows the magnitude of current or voltage signals with respect to time. By displaying the waveform of a signal on an oscilloscope, the time between cycles can be measured and its frequency can be calculated.
Waveform monitor - A special oscilloscope used to display and analyze electrical (voltage or current) signals.
Waveguide - An acoustic device built into a loudspeaker enclosure that improves the efficiency of the speaker by confining the movement of a sound wave to travel over a desired path. In brief, a waveguide is a tube-like structure, straight or folded, that couples the motion of the loudspeaker cone to the motion of the air in the tube. This allows a small speaker driver to create clear sound, without distortion, even at the high volume levels required for low frequency reproduction.
Waveguide Dispersion - The distortion of an electromagnetic signal, or in the case of fiber optics, light as it encounters a waveguide and is dispersed into multiple components of different modes or wavelengths.
Wavelength - The distance from one peak to the next between identical points in adjacent waves of electromagnetic signals propagated in space or along a wire. Wavelength is usually specified in meters, centimeters, or millimeters. In the case of infrared, visible light, ultraviolet, and gamma radiation, the wavelength is usually specified in nanometers (10e-9 meter) or Angstroms (10e-10 meter). Wavelength is inversely related to frequency. The higher the frequency of the signal, the shorter the wavelength.
Wavelength Division Multiplexing – WDM - The combination of two or more optical signals at different wavelengths for transmission within a single optical fiber.
Weighting filter - A special type of band-limiting filter used in measuring audio loudness levels that “weights”, or gives more attention to, certain frequency bands. Common weighting filter designs include: A-weighting, a wide bandpass filter, centered at 2.5 kHz, that mimics the way we hear (see “Fletcher-Munson Curve”); and C-weighting, generally “flat” frequency response with -3 dB attenuation at 31.5 Hz and 8 kHz.
White - The lightest visible surface created by a reflection of all colored light.
White level - In television, the signal level that corresponds to the maximum picture brightness. The white level is set by the contrast control.
White light - A blend of multiple colors of the visible portion of electromagnetic spectrum, resulting in light that is white in color to the human eye.
White noise - Noise with random amplitude (strength) over a wide frequency range. Used to test speakers for resonance and sensitivity. Low levels of white noise can be used to cover up other random noises, for example, in an open office environment.
Wideband - A relative term indicating a high bandwidth.
Wipe - A visual transition between images during which the edge of one image moves across the screen revealing the next image.
WLAN - Wireless Local Area Network. A form of local area network that uses radio waves to transmit data between nodes rather than through cable. Mobile devices, such as laptop computers and personal digital assistants, have helped spawn the “plugless” connection to WLANs. The IEEE 802.11 standard specifies the technologies for wireless LANs.
Woofer - A loudspeaker designed to reproduce low frequencies.
Workstation - A type of computer used in design or development work, such as engineering and CAD, requiring a moderate amount of computing power and high-resolution graphics.
Wow - A low pitch audio artifact caused by speed fluctuation in the playback device. See “Flutter.”
Wrap-around - A video problem that occurs when the left picture information is displayed on the right side of the screen and the right picture information is displayed on the left side of the screen, separated by a vertical bar.
WSXGA - “Wide-SXGA” defines a class of SXGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined as the number of individual dots that a display uses to create an image. These dots are called pixels. A WSXGA display has 1920 to 1600 horizontal pixels and 1080 to 900 vertical pixels respectively that are used to compose the image delivered by the projector.
WWW - World Wide Web. An international network of subscriber sites where information in the form of text and/or graphics is made available to computer users (Web site visitors).
WXGA - “Wide-XGA” defines a class of XGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined as the number of individual dots that a display uses to create an image. These dots are called pixels. A WXGA display has 1366 to 1280 horizontal pixels and 768 to 720 vertical pixels respectively that are used to compose the image delivered by the projector.
XGA - eXtended Graphics Array card. IBM’s graphics standard that includes VGA and extended resolutions up to 1024 x 768 (interlaced 35 kHz). This card uses a 15-pin HD VGA-style connector.
XGA-2 - eXtended Graphics Array card, 2nd generation. Capable of scanning from 31 to 68 kHz and resolutions up to 1600 x 1200 pixels, this card uses a 15-pin HD VGA-style connector.
XLR connector - XLR connectorA type of audio connector featuring three leads: two for the signal and one for overall system grounding. A secure connector often found on high quality audio and video equipment. Also called a “cannon connect"
xvYCC - Extended-gamut YCC color space. xVYCC can be used in the electronics of televisions and other video displays to improve the image quality of high-definition video signals.
Y - Luminance or luma.
Y Cr Cb - Describes the color space for digital component video. See “Y, R-Y, B-Y.”
Y Pb Pr - Describes the color space for progressive-scan (non-interlaced) component video. See “Y, R-Y, B-Y.”
Y signal - The luma signal transmitted in standard color video. In a color picture, the Y signal is made up of 0.30 red, 0.59 green, and 0.11 blue. It is compatible with a standard monochrome receiver.
Y to C delay - Relative delay or timing of the luminance channel compared to the chrominance channel in a video system.
Y, R-Y, B-Y - Color difference signal designation. Y corresponds to the luminance signal; R-Y corresponds to the red minus luminance signal, and B-Y corresponds to the blue minus luminance signal. After luminance is subtracted from red and blue, the remainder is considered to be the green portion of the RGB video signal. These signals are derived as follows: Y = 0.3 red + 0.59 green + .11 blue; R-Y = 0.7 red - 0.59 green - 0.11 blue; B-Y = 0.89 blue - 0.59 green - 0.3 red
Y/C - The technical description of S-video. The luminance signal, Y, and the chrominance signal, C, are carried on separate signal/ground pairs. Because the Y channel is carried separately, higher bandwidth is possible and color subcarrier crosstalk is eliminated.
Y/C separator (YCS) - A Y/C separator isolates the luma (Y) and chroma (C) components of a composite video signal. This is the first step necessary in decoding composite video.
YUV - Describes the color space used in television transmission and motion video production and playback. See Y, R-Y, B-Y
Z - A symbol for impedance.
Zipcord - A cable comprising two jacketed wires or optical fibers that are conjoined together and can be separated.
Zoom - A term used with cameras and video displays related to the ability to change the view anywhere between near and far. Definitions for near and far vary from one device to another.
Zoom lens - A lens with a variable focal length.