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- A/A ROLL EDITING
- Editing from a single video source using effects to transition from the source to itself (source "A" to "A") using a picture freeze at the end of one scene to transition the start of the next scene.
- A/B ROLL EDITING
- Editing from two video sources ("A" and "B") to a third record VCR. Typically a switcher is used to provide transition effects between sources. Control over the machines and process can be done manually or automatically using an edit controller.
- A/D CONVERTER (Analog-to-Digital Converter)
- A device that digitizes an analog waveform.
- AAF (Advanced Authoring Format)
- Absolute time - normal time in terms of hours, minutes, seconds and milliseconds.
- A:B:C Notation
- The a:b:c notation for sampling ratios, as found in the CCIR-601 specifications, has the following meaning:
- 4:2:2 means 2:1 horizontal downsampling, no vertical downsampling. (Think 4 Y samples for every 2 Cb and 2 Cr samples in a scanline)
- 4:1:1 ought to mean 4:1 horizontal downsampling, no vertical. (Think 4 Y samples for every 1 Cb and 1 Cr samples in a scanline) It is often misused to mean the same as 4:2:0.
- 4:2:0 means 2:1 horizontal and 2:1 vertical downsampling. (Think 4 Y samples for every Cb and Cr samples in a scanline)
- A-CHARACTERS
- A character set used in the ISO 9660 Volume Descriptors. It consists of capital letters A to Z, digits 0 to 9, and the following symbols: (space)! " % & '()=*+,-./:;<?>_
- AC-3
- A term synonymous with Dolby Digital.
- ACCESS TIME
- The time it takes to retrieve a piece of information. With hard disks and compact discs, maximum access time is measured as the time it takes to move from one end of the disc to the other, find a piece of information, and transfer that information to RAM.
- ACN (Active Combining Network)
- The time relationship between two or more sound waves at a given point in their cycles.
- ACOUSTICAL PHASE
- The time relationship between two or more sound waves at a given point in their cycles.
- ACOUSTICS
- The science that deals with the behavior of sound and sound control. The properties of a room that affect quality of sound.
- ADPCM (Adaptive Delta Pulse Code Modulation)
- An audio encoding compression technique which encodes the difference between the predicted value of the signal instead of the absolute value of the original waveform so that the compression efficiency is improved. This difference is usually small and can thus be encoded in fewer bits than the sample itself. Used in CD-I and CD-ROM XA recording.
- ADR (Automated Dialogue Replacement)
- A technique used to rerecord dialogue in synchronization with picture in post-production. The picture is automatically replayed in short "loops" again and again so that the actors can synchronize their lip movements with the lip movements in the picture and then record the dialogue. Also known as automatic dialog recording and looping.
- AES/EBU
- Acronym for the dual-channel digital audio interface jointly conceived by the Audio Engineering Society and the European Broadcasting Union and defined by Standard IEC-958. This interface is usually found on professional equipment with connections made via XLR-type (3-pin) connectors. (See S/PDIF)
- AES31 (AES31-3)
- A proposed AES (Audio Engineering Society) standard for digital audio project interchange.
- ADAT (Alesis Digital Audio Tape)
- An 8-channel digital audio tape recorder format utilizing S-VHS videocassettes, developed by Alesis.
- ADL (Audio Decision List)
- A sample-accurate EDL generated by a DAW rather than a video editing system.
- AIFF (Audio Interchange File Format)
- An uncompressed digital audio (waveform) data file format supporting a variety of bit resolutions, sample rates and audio channels and widely used in professional applications that process digital audio waveforms. This format is popular on the Apple Macintosh platform as it takes into account some peculiarities of the PowerPC CPU such as big endian byte order.
The AIFF (or AIF) file itself consists of a number of required and optional “chunks” of information: The FORM chunk which identifies the file as a AIFF file, the COMMON chunk which identifies parameters such as it’s length and sample and the SOUND DATA chunk which contains the actual data (samples). All other chunks are optional. Among the other optional chunks are ones which define markers, list instrument parameters, store application-specific information, etc.
- AGC (Automatic Gain Control)
- Circuitry used to ensure that output signals are maintained at constant levels in the face of widely varying input signal levels. AGC is typically used to maintain a constant video luminance level by boosting weak (low light) picture signals electronically. Some equipment include gain controls which are switchable between automatic and manual control.
- ALC (Automatic Level Control)
- Circuitry used to automatically adjust the audio recording level to prevent excessive volume. Excessive ALC has a tendency to introduce noise and hiss onto the audio tracks. Some equipment include level controls which are switchable between automatic and manual control. Used in video and audio equipment to ensure that output signals are maintained at constant levels in the face of widely varying input signal levels.
- ALIASING
- Undesirable signals added to and interfering with an originating electronic signal.
- In audio, frequencies generated by inadequate digital filter sampling circuitry, harmonically unrelated to the original signal.
- In video, display effects caused by too much high frequency video information. Examples are:
- Temporal aliasing - e.g., rotating wagon wheel spokes apparently reversing direction
- Raster scan aliasing - e.g., twinkling or strobing effects on sharp horizontal lines
- Stair-stepping - Stepped or jagged edges of angled lines, e.g., at the slanted edges of letters.
- AM (Amplitude Modulation)
- Amplitude modulation is a process used for some radio (AM broadcast) andtelevision video transmission. A low frequency (program) signal modulates (changes) the amplitude of a high frequency RF carrier signal (causing it to deviate from its nominal base amplitude). The original program signal is recovered (demodulated) at the receiver. This system is extensively used in broadcast radio transmission because it is less prone to signal interference and retains most of the original signal quality. In video, FM is used in order to record high quality signals on videotape.
- AMBIENCE
- Sounds such as reverberation, noise, and atmosphere that form a background to the main sound. Also called room tone, presence and atmos in Great Britain.
- AMPLITUDE
- The magnitude of a sound wave or electrical signal, measured in decibels.
- ANALOG
- An adjective used to describe a method of converting audio and video information to a continuously varying voltage or magnetic field representing the original data. The term is used mainly to differentiate established data storage methods of the 1960s and 1970s from the newer digital storage methods. Information stored in analog form is subject to generation losses and degradation due to noise, distortion and other electronic phenomena over time.
Examples of data stored in analog form are the VHS and 8mm videotape formats with typical video signal levels within the 0.7 - 1V (volt) range. (See DIGITAL)
- ANALOG MONITOR
- A television set, which cannot receive TV broadcasts because of its lack of a TV tuner, which accepts only analog signals. Several types of signal formats are accepted by analog monitors: composite video, RGB & sync, Y/C, YUV and any combination of these formats. The signals transmitted to an analog monitor are usually between 0 and 1V (volt) and use 75 ohm coaxial cables.
- ANECHOIC CHAMBER
- A room designed to eliminate all reflected sound. This is accomplished through design and with materials which dissipate and absorb sound waves.
- ANSI-LABELED
- A tape recorded with a file structure and tape label system which defines the Volume name and file header for the information contained in the tape, according to ANSI (American National Standards Institute) specification X3.27-19778. Most disc manufacturers prefer ANSI-labeled tapes.
- ANSI-UNLABELED
- A tape recorded with a file structure, but without the ANSI tape labels.
- ANTI-ALIASING
- The process of electronically reducing aliasing, especially letters and genlocked graphic elements.
- APERTURE
- An adjustable opening in a lens which affects the amount of light entering a camera. The size of the aperture is controlled by the iris adjustment and is measured in f-stops. Smaller f-stop numbers pass more light to the surface of the camera’s pickup device.
- ASIO (Audio Stream Input Output)
- A standardized communication protocol between audio software and hardware, developed by Steinberg Media Technologies to bypass the problem of potentially high operating system/monitoring latency (time delay). It enables audio hardware manufacturers to write optimized drivers for their hardware. For a user, the knowledge that an ASIO driver exists for a particular piece of hardware, is a sign that there will be a performance boost, compared with the same audio card configured to use an operating system’s own mechanism.
- ASPECT RATIO
- The ratio between the height and width of the TV picture on the screen. The aspect ratio for a standard TV or video monitor is 4 to 3 (4:3). The HDTV video format has an aspect ratio of 16 to 9 (16:9).
- ASPI (Advanced SCSI Programmer’s Interface)
- Set of software primitives and data structures which allow software using the ASPI interface to be SCSI host adapter-independent.
- A-TIME (Absolute Time)
- Elapsed time measured in minutes, seconds and frames, referenced to the program start (00:00:00) on a CD, CD-DA or DAT. Can be used in determining the start and stop times of sound segments for programming an application on a mixed-mode disc, measuring from the very beginning of the data area (including the computer data in Track 1).
- ATM (Asynchronous Transfer Mode)
- Describes the ways a digital audio word may be transmitted (either big endian or little endian). If a word is presented most significant bit first, it is big endian. If presented least significant bit first, it is little endian.
- ATTACK TIME
- The length of time it takes an audio limiter or compressor to respond to the input signal. (See DECAY TIME)
- AUDIO
- The audible portion of any multimedia material consisting of frequencies corresponding to a normally audible sound wave (20 Hz to 20,000 Hz). Also the "soundtrack" of a videotape.
- AUDIO BANDWIDTH
- The range of audio frequencies which directly influence the fidelity of a sound. The higher the audio bandwidth, the better the sound fidelity. The highest practical frequency which the human ear can normally hear is 20 kHz. An audio amplifier which processes all frequencies equally (flat response from 20 Hz to 20 kHz) and a reasonably high signal-to-noise ratio, will faithfully reproduce the full range of perceptible sound.
- AUDIO-FOLLOW-VIDEO
- During video recording, the video signal is usually accompanied by an audio signal. Sometimes, during video editing, it is often necessary to separate the audio from the video signal. Audio-follow-video mixers allow accompanying audio to "follow" the video when switching video sources.
- AUDIO LEVELS
- Proper audio levels are crucial. If the audio level is too high when recording, overload of the input electronics will cause audio distortion. If audio levels are too low, the signal-to-noise ratio deteriorates. Audio levels are typically indicated either by mechanical VU-meters or electronic LED bar graph meters.
- AUTHORING
- The process of preparing, assembling and linking audio, video and graphics (assets), with the addition of a user interface, into a cohesive, interactive entertainment product. The end product of authoring is usually inclusion on either a DVD or CD-ROM disc.
- AZIMUTH
- Physical alignement attribute of analog tape recording (record and playback) heads. Adjustment is made so that their centerlines are parallel to each other and at right angles to the direction of the tape motion passing across the heads. Record to playback misalignment causes phase and high-frequency amplitude degradation of the audio signal.
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