Grass Valley Dictionary Grass Valley Dictionary

Dictionary of Technical Terms - A

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A-B editing
See A-B roll.

A-B roll
Videotape editing arrangement in which scenes on tape are played alternately on VTRs A and B and recorded on VTR C. Typically, the final output recorded on VTR C contains some scenes from VTR A and some scenes from VTR B with transitions (cuts, mixes, wipes etc.) between the scenes.

absorption loss

In telecommunications, attenuation of the optical signal within the fiber optic transmission medium. Usually specified in terms of dB/km.

AC (ac)

Alternating current.

AC coupling

A method of coupling one circuit to another through a capacitor or transformer so as to transmit the varying (AC) characteristics of the signal while blocking the static (DC) characteristics. In some analog GVG distribution amplifiers, when the AC coupling mode is selected, a feedback loop maintains the output signal at an average DC level of 0 volts regardless of APL (average picture level) or DC offset of the incoming signal.

AC/DC coupling

May also be called simply DC coupling. Coupling between circuits which accommodates the passing of both AC and DC signals.


See key accumulation.

accumulative latch

A feature of some GVG keyers that allows combining of several key sources in a single keyer.

active picture period

That portion of the video signal that produces the viewable part of the television picture as distinguished from that portion of the video signal that occurs during blanking (horizontal and vertical retrace).

active video

The portion of a video signal that contains picture information.

active window

The window in a software application that is currently selected for use.


Able to adjust or react to a video condition or application, as an adaptive circuit. This term usually refers to filter circuits.

ADC (A-D, A/D, A-to-D)

Analog-to-digital converter.

additive key

Method of keying in which two complementary video signals that have already been shaped by multiplication with a key signal are added to create a composite image.

additive mix

Addition of two video images together without attenuation of either signal.


1. A precise frame location on a videotape, usually identified by a time code number. 2. A memory location or device identifier in microprocessor and computer terminology.


Audio Engineering Society.


Informal name for a digital audio standard established jointly by the AES and EBU organizations. The sampling frequencies for this standard varies depending on the format being used; the sampling frequency for D1 and D2 audio tracks is 48 kHz.


Audio follow video.


Automatic gain control.




To broadcast a signal.

alarm indication signal (AIS)

In telecommunications, an all 1's signal (generally) generated by in-line equipment to indicate to down line devices that an input has failed. See also blue signal.


A storage place within a video editing application for cataloguing and archiving clips, effects, and other production elements.


Defects or distortion in a television picture. In analog video, aliasing is typically caused by interference between two frequencies such as the luminance and chrominance frequencies or the chrominance and field scanning frequencies. It appears as moire or herringbone patterns, straight lines that become wavy, or rainbow colors (See cross color). In digital video, aliasing is caused by insufficient sampling or poor filtering of the digital video. Defects are typically seen as jagged edges on diagonal lines and twinkling or brightening in picture detail.


The adjustment of components in a system for optimum performance.

all inputs hostile

Measurement technique, particularly for crosstalk, using worst case conditions (typically, full chroma signal on all inputs other than the one under test).

all ones

A digital signal consisting of data that contains all logical ones. In telecommunications, a test signal consisting of 11111.


A display symbol set consisting of the twenty-six letters of the alphabet and the digits 0 through 9.

alternate mark inversion (AMI)

In telecommunications, an encoding protocol where successive data 1's are transmitted as alternate, equal positive and negative pulses, and data 0's are sent as spaces, each of zero amplitude.


Ante meridiem.


Amplitude modulation.

ambient temperature

The temperature of the surrounding medium, typically the air, which comes into contact with a device. Room temperature.

A-mode assembly

See sequential assembly.

amp (A)

1. Ampere.

ampere (A)

Unit of measure of electrical current.


A connector manufacturer.


The magnitude of a signal in voltage or current. Frequently expressed in terms of peak, peak-to-peak, or RMS.

amplitude modulation (AM)

A method of imposing information on a carrier signal, such as a sine wave, by varying its amplitude.


1. An adjective describing any signal that varies continuously as opposed to a digital signal, which contains discrete levels. 2. A system or device which operates primarily on analog signals.

analog component

Another name for component video, such as RGB or Y, R-Y, B-Y, as opposed to digital component video. See component video.

analog component island

A discrete set of analog component equipment within a non-component facility.

analog-to-digital converter

A circuit that uses digital sampling to convert an analog signal into a digital representation of that signal.


A feature of some video devices, such as character generators, which minimizes aliasing by filtering and other techniques. See aliasing.


Alternate Operator Service.

aperture correction

The enhancement of a video signal to increase image sharpness. Aperture correction is employed to compensate for the finite size of a scanning beam or a pixel.


Avalanche photodiode.

APL (average picture level)

The average level of the active video (portion of video between blanking pulses), expressed as a percentage or in IRE.

append mode

In video devices capable of creating key frame effects, a mode that permits new key frames to be added to an existing key frame effect to make the effect longer.


A software package that runs on a computer system.

application window

The main or home window displayed by a software application from which other subordinate windows are accessed.


1. Internal organizational (circuit) structure of an electronic product. 2. Physical layout and interconnection scheme of a studio.


Off-line storage of video/audio onto backup tapes, floppy disks, optical disks, etc.


Undesirable elements or defects in a video picture. These may occur naturally in the video process and must be eliminated in order to achieve a high-quality picture. Most common are cross color and cross luminance.


American Standard Code for Information Interchange. A standard code for transmitting data, consisting of 128 letters, numerals, symbols, and special codes each of which is represented by a unique binary number.


Application specific integrated circuit. An integrated circuit designed for special rather than general applications.

aspect ratio

1. The ratio of television picture width to height. In NTSC and PAL video, the present standard is 4:3. 2. The ratio of wipe pattern width to height.


1. A manufactured part made by combining several other parts or subassemblies. For example, a cable assembly consists of the cable with connectors at each end. 2. Assembly language.

assemble edit (assemble mode)

An editing mode that replaces all signals on the record tape (video, audio, control, and time code tracks) with new signals. See also insert edit.

assembly language

A symbolic computer language in which a programmer can create programs that the computer's assembler program will translate into machine language for controlling the computer. Assembly language is a higher level language one step above machine language.


Lacking synchronization. In video, a signal is asynchronous when its timing differs from that of the system reference signal. A foreign video signal is asynchronous before it is treated by a local frame synchronizer.


Asynchronous Transfer Mode. A data transmission scheme using self-routing packets of 53 bytes, 48 of which are available for user data.

atomic frequency standard

In television, an extremely accurate means of timing using an atomic clock.


Audio tape recorder.


Advanced Television Systems Committee (USA). A group whose charter is to develop voluntary national standards for high definition television.


A physical channel of a digital picture manipulator is attached to a logical channel of a controller if the physical channel is successfully acquired by the controller. A physical channel may be attached to only one logical channel of one controller at a time.


The decrease in amplitude of a signal.


A circuit that reduces signal amplitude.


Advanced television. High resolution digital television, several versions of which are in proposal stages in the US and Europe.


Sound. An electrical signal that carries sound information.

audio bridge

In telecommunications, a device that mixes multiple audio inputs and feeds back composite audio to each station, minus that station's input. Also known as a mix-minus audio system.

audio crosspoint module

Circuit board containing crosspoints for audio signal switching.

audio distribution amplifier (audio DA)

A device used to replicate an audio signal, typically providing 6 outputs, each of which is identical to the input signal.

audio-follow-video (AFV)

An operational mode in which audio and video switchers are tied together so that when the operator selects the video source, the audio simultaneously and automatically switches to the same source.

audio over

See over.

auto assembly

In video editing, the editing system automatically records all edits listed in the edit decision list. This allows the operator to complete an edit decision list and then let the editing system perform all of the recording automatically.

auto clean

A feature of GVG editors that automatically cleans the edit decision list during the course of editing. This removes duplicate or overlapping edits so that over-recordings are eliminated. See 409.


A feature of GVG editors that automatically finds a match to the last record VTR edit and inserts the match at the proper VTR in the mark table.

automatic changeover switch

Equipment that monitors the outputs of two sync generators (one in-use and one backup) and automatically switches to the backup sync generator should there be a failure of the sync generator in use.

auto select key

A feature of some video keyers that automatically selects the key source when the operator selects the key fill.

auto setup

A feature of some GVG chroma keyers that automatically adjusts the chroma key after the operator identifies the chroma key background color using a cursor.


Capability of some digital video equipment to automatically adjust input video timing to match a reference video input. Eliminates the need for manual timing adjustments.

auto transition

On a video switcher, an automatic transition where the motion of the lever arm is electronically simulated.


In some GVG editing systems, AutoTrim allows two adjacent video clips to be trimmed at the same time. The in point of one clip is trimmed at the same time that the out point of the adjacent clip is trimmed.

auxiliary bus

A single crosspoint bus, typically used in conjunction with a production switcher. Often used to feed a digital picture manipulator with the same inputs as the primary inputs applied to the switcher.

auxiliary channel (aux)

In a video editing system, a channel reserved for connecting an external audio and/or video device.

avalanche photodiode

Electronic device used as a detector in some fiber optic transmission systems.


American Wire Gauge.


Relating to digital picture manipulation, the X axis is a horizontal line across the center of the screen, the Y axis is a vertical line, and the Z axis is in the third dimension, perpendicular to the X and Y axes and indicates depth and distance.
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