AC-3
ACC
ACTIVE VIDEO
ADAPTIVE COMB FILTER
ADC
ADTV
AES 3id
AES/EBU
AGC
ALARM CAMERA SCANNER
ALIASING NOISE
ALPHA CHANNEL
ALPHA MIX
AMORPHEOUS LCD
AMPLITUDE MODULATION
ANALOG MONITOR
ANALOG VIDEO SIGNAL
ANAMORPHIC SIGNAL / DVD
ANCILLARY DATA
ANIMATION
ANSI
ANTIALIASING
AP – ACCESS POINT
APERTURE
APERTURE GRILL
APL
ASPECT RATIO
ATV
AUDIO
AUDIO BANDWIDTH
AUDIO DUB
AUDIO EDITING
AUDIO EQUALIZATION
AUDIO EXCITER
AUDIO MIXING
AUDIO NOISE
AUDIO-FOLLOW-VIDEO SWITCHER
AUDIO-VIDEO
AUDIO-VIDEO COMBINER
AUTOMATIC NOISE GATE
AVI
AC-3
A digital surround-sound system introduced by Dolby™ laboratories. The system is usually comprised of 5.1 channels (6.1 nowadays and counting)- five/six discrete channels - left, right, center/s, back left and back right. In addition one Subwoofer covers the bass (low frequency signals, representing a limited spectrum of audio, hence the .1 designation) that belongs to all channels. As the ear is not sensitive to the direction of the very low frequencies, the ''low-bass'' area, one Subwoofer is sufficient. In order to retrieve and decode AC-3 sound channels, a special amplifier/receiver is needed. The AC-3 system is also available on some digital video equipment for recording and playback, such as a DVD. Similar digital 3D sound schemes are also available such as THX®, DTS® and others, as well as Dolby surround, which is an analog scheme.
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ACC
Automatic Chroma Correction. A system built into some VCRs and TV sets for automatic adjustment of color saturation levels. Most ACC systems measure the Color Burst amplitude and use it as reference. As the system is automatic, erroneous color levels can appear in the video scene - an original grayish scene can become over colored, or a rich, saturated-color scene can become dull.
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ACTIVE VIDEO
The part of a video signal visible on the screen.
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ADAPTIVE COMB FILTER
A Comb Filter that uses adaptation technology - changing its operation parameters by dynamically following changes in the picture.
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ADC
(рус. АЦП)
Analog to Digital Converter. A device which converts an Analog signal to a digital form. The process may be done with different levels of accuracy. The conversion fidelity is dependent on two factors - sampling rate and number of bits. The higher the rate and/or bits used during conversion, the more accurately the analog signal is reproduced. Until recently, the most common video sampling speed was four times the color subcarrier frequency (4xFsc - 17.7 Msamples/sec for PAL 14.3 Msamples/sec for NTSC) Today, the standard (industrial and broadcast) tends to be 13.5 Msamples/sec for luminance signals. For color difference signals it is usually half for both PAL and NTSC. Industrial video signals are digitized at 8-bit accuracy (256 levels) while broadcast signals are digitized at 10-bit accuracy (1024 levels) or even at 12 bit. Hi-Fi audio signals are usually sampled at double the highest frequency audible to the human ear, i.e., 20 kHz (or more - sampling at 44 kHz or even higher frequencies) with an accuracy of 16 bits or more.
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ADTV
(рус. АЦП)
Advance definition Television. The “HDTV” standard which was used in Japan. “True” HDTV is now replacing this format worldwide.
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AES 3id
(рус. АЦП)
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AES/EBU
(рус. АЦП)
A digital audio standard established by the Audio Engineering Society and the European Broadcasting Union. The signal is serial digital, comprising two channels. The basic sampling resolution is from 16 to 24 bit, sampled at frequencies between 32 kHz and 192 kHz (44.1 kHz is the most common). Two sets of 4 bits of information are included for other data transmission (one set can be added to the 20 bit of audio, for a 24 bit system). Additional bits are transmitted as well, and the transmitted frames of the interwoven audio channels are grouped to frame blocks.
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AGC
(рус. АРУ)
Automatic Gain Control. Electronic circuitry that assures a fixed predefined output level, automatically compensating for varying input levels. Used in audio, video and RF equipment to ensure that output signals are maintained at constant levels in the face of wide variations in the signal-input levels. Low level signals are boosted and high level signals are attenuated to an average level. Automatic gain control has a tendency to introduce audio noise and hiss into the audio channel of a videotape. In sophisticated equipment, automatic gain control is often superfluous, and the user can select the option of manual control
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ALARM CAMERA SCANNER
An electronic device, mainly used in security installations, where several video cameras positioned in different locations on the premises, scan automatically, and are viewed one after the other on one monitor. When an intrusion occurs in the field-of-view of one of the cameras, a special alarm signal is sent to the scanner instantly activating the particular camera in question. It usually triggers an additional alarm device drawing attention to the event. Sophisticated scanners have internal microprocessor control, allowing them to skip or analyze every scanned source, as well as activating, when necessary, a special device, which relays a suspicious camera image to a remote location for monitoring via a telephone line.
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ALIASING NOISE
An artifact created when an ADC converts an analog signal to digital form and the sampling rate of the converter is less than double the highest frequency component within the analog signal.
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ALPHA CHANNEL
The Alpha channel is a separate channel of data, transmitted alongside the original color or video information - whether it is video or computer based. It is used to specify an Alpha value for each color pixel in order to control pixel based image blending and mixing. Values of the Alpha channel range between 0 and 1.
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ALPHA MIX
Image blending and mixing based and controlled by the Alpha Channel data stream.
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AMORPHEOUS LCD
An obsolete LCD display system, suffering from many technical flaws, replaced by polysilicone-type and other active displays.
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AMPLITUDE MODULATION
Amplitude Modulation, AM, is used when a signal, (usually an RF signal) is transmitted carrying low frequency information. The low frequency signal modulates -(changes) the amplitude of the RF signal, and is recovered (detected) at the receivers end. Video information that is transmitted on the air as TV transmission employs this system. Some radio stations use it also (AM Broadcast), although the superior FM system dominates radio transmissions.
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ANALOG MONITOR
A video monitor which accepts analog level signals. Several types of inputs are accepted by analog monitors making them very flexible: composite video, RGBS, YC, YUV and any combination of these standards. The signals transmitted to an analog monitor are usually between 0 and 1 Volt and use 75-ohm coaxial cables.
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ANALOG VIDEO SIGNAL
Signal in which the output varies as a continuous function of the input, while the values of the transmitted information are within defined limits. Any variation in an analog video signal may represent a specific video parameter, e.g., when the luminance signal is high (0.7 V above black level) the picture is very bright. When the signal is low (0.1 V), the picture is very dark, at 0 V the picture is totally black. TTL digital signals, in contrast, are predefined as only 0 or 5 V or other fixed logic levels, and do not vary.
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ANAMORPHIC SIGNAL / DVD
The anamorphic horizontal compression system used in the cinema industry, optically compresses the wide-screen movie frames by a special lens, to fit on a standard film (35mm or similar). When displayed on the screen, the opposite effect is used – stretching the frames to the original wide-screen format. In the DVD format, a similar process takes place, where the frames are digitally compressed horizontally on the disc. When played on a standard, 4:3 aspect TV, a letterbox image is shown, but when set to 16:9, a full wide-screen image is shown on a Plasma screen or video projector which is capable of 16:9 image reproduction.
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ANCILLARY DATA
Data added to a digital video data stream including information such as embedded digital audio, control signals, etc.
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ANIMATION
Originally, creation of the appearance of movement, such as in a cartoon by flipping a series of gradually varying drawings in rapid sequence. Today, creating animation and cartoons is done more effectively using computers with appropriate graphics software and genlocking hardware. The final product of computerized animation can be integrated into videotapes or a video production using encoding equipment.
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ANSI
American National Standards Institute.
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ANTIALIASING
Antialiasing is a procedure which, by smoothing and filtering, eliminates or reduces, aliasing noise. The procedure usually involves low pass filtering of the processed signal prior to digitizing in order to eliminate signals, having frequencies close to and greater than half of the sampling frequency.
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AP – ACCESS POINT
A device (a PC card or a standalone machine) that bridges the wireless network to the wired one.
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APERTURE
An adjustable opening that effects the amount of light entering a camera. The aperture (sometimes referred to as the Iris) is measured in F-stops. Smaller F-stop numbers mean that more light reaches the optical sensing device of the camera.
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APERTURE GRILL
The screen structure element of Sony Trinitron-™ monitors.
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APL
Average Picture Level. A measure of average video luminance level expressed as percent of maximal white level. When the APL is low, the picture is dark, when the APL is high the picture is bright.
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ASPECT RATIO
The ratio between the width and height of the TV picture on the screen. In a normal TV set or monitor the aspect ratio is 4 to 3 (4:3). The new aspect ratio in HDTV and IDTV/EDTV is 16:9 which resembles the aspect ratio in a movie theatre (Widescreen). New TV systems support both 4:3 and 16:9 aspect ratios (PAL PLUS) and can automatically switch between them.
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ATV
Advanced Television. A digital television system comprising standard, enhanced and high-definition versions.
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AUDIO
(рус. Аудио)
Pertaining to frequencies of a normally audible sound wave (15 to 20000Hz). Audio has been, until recently, a very neglected side of video recording and processing. Very often, during videotape duplication and enhancement, the quality of the soundtrack is detrimentally affected. Several special soundtrack enhancement devices and integrated audio and video enhancers have recently appeared on the market (see Audio Equalization and Audio Exciter). New VCRs and TV systems employ Hi-Fi quality sound tracks, and are sometimes equipped with decoders for DOLBY SURROUND, AC-3 or other three-dimensional sound encoding devices.
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AUDIO BANDWIDTH
The range of audio frequencies over which an amplifier or receiver will respond and provide useful output. The higher the audio bandwidth the better the sound quality. The highest practical frequency for the human ear is 20 kHz. An audio amplifier delivering a flat response of up to 20 kHz will faithfully reproduce the audio soundtrack of a video recording.
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AUDIO DUB
A feature used in video editing to add, replace, or mix audio signals with the original sound track without affecting the picture (video portion). Special controls and connectors are available for this purpose on some quality video recorders. When dubbing is not available on, or is limited by, the video recorder, audio dubbing can be performed externally using audio/video processors.
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AUDIO EDITING
Combining audio material of different origin into one continuous piece. For example, when a sound track is added to a videotape, various background sounds, music and speech may be supplemented in order to highlight particular scenes in a movie. Audio correction can also be done during video editing. Audio equalization, audio noise reduction, Dolby encoding, etc. are functions available on many quality editors.
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AUDIO EQUALIZATION
An audio process, hardware or software based, which breaks down the audio spectrum into several frequency bands to compensate for changes in audio frequency-dependent levels, allowing the user to control (boost or cut) each frequency segment individually. The main use of audio equalizers is to compensate for inadequate acoustics in the room where the sound is being played. Another very important use for audio equalization is to revitalize the playback characteristics of low quality tapes and poor recordings in order to recreate the original sound.
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AUDIO EXCITER
An audio circuit available in high quality audio equipment, designed to recreate the harmonic content of an audio signal which was lost during video or audio tape duplication. Using the audio exciter to recreate the lost harmonic content, generates a sparkling audio sound. This effect is different from normal high frequency boosting which generates noise and hiss while improving the frequency response of the audio signal. Audio exciting is available only on special sound correction devices.
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AUDIO MIXING
The mixing or blending of two or more audio signals to generate a new signal, which is often used for audio dubbing. Audio mixing requires that all audio channels involved are amplified and equalized to the same level. To mix a line level input with a microphone signal, the microphone signal must be pre-amplified to bring it up to a level similar to that of the line signal. In video processing, audio mixing is used for the insertion of background music behind the dialogue. It is also employed in the creation of cross fading between two audio sources. It produces a drift in the level of the received signals until one fades out and the second becomes dominant.
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AUDIO NOISE
A hiss (random high frequency noise) or a hum (low frequency noise from the power-line frequency and its harmonics or ground loops) heard on audio or video equipment. It is the result of poor signal handling or of discrepancies between audio pickup devices and media. Audio noise reduction circuitry eliminates or reduces audio noise.
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AUDIO-FOLLOW-VIDEO SWITCHER
During video production, the video signal is normally accompanied by an audio signal. Sometimes, during the switching or processing of signals, the audio signal is separated from the video signal. In such a case, a complex situation arises whereby each signal must be processed, mixed and enhanced separately. Audio-follow-video is a process which overcomes this difficulty and both signals, audio and video, are switched from an audio-video source to an audio-video acceptor simultaneously (not in separate passes).
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AUDIO-VIDEO
A term which was often used when discussing a channel on a TV receiver or on video equipment, which has been especially designed to accept VCR audio-video signals. This channel automatically activates special circuitry within the TV set or monitor to prevent picture distortion and skewing. It is also used for audio-video processors, which handle both types of signals. The AV definition (Audio-Video) has broadened since then and now describes anything that handles both signals simultaneously.
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AUDIO-VIDEO COMBINER
A device which combines audio and video signals. In the analog world it describes a machine, which modulates the audio signal on a high frequency carrier and mixes it with the video signal for transmission on a single cable. In the digital world it describes a device which embeds digital audio signals within a digital video signal.
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AUTOMATIC NOISE GATE
A unique feature, available only on Kramer equipment, which provides optimal automatic suppression of snow (signal noise level) during any stage of video enhancement (See Noise Gate.)
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AVI
Audio Video Interleaved. A computer video/graphics format. This format interleaves digitized video frames (or computer-generated frames) and synchronized audio in one file. The clips generated in the AVI format may be played back in a Windows® equipped PC, usually independent of screen resolution and color palette. This also denotes a practically uncompressed file format obtained for example in a PC, when digital or analog video and audio are captured from an external source. As it is uncompressed, it can occupy up to 200 MB of disk space for every minute of captured video.
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