Technical Glossary
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Displaying 104 glossary terms found.


The first of two essential parts of a theatre’s sound playback system, consisting of the film soundtrack, the projector soundhead, and signal processing including noise reduction and multichannel decoding (i.e., Dolby A and Dolby Stereo, respectively). Dolby Digital and SDDS digital on-film formats are read by a projector-attached soundhead that is decoded in the appropriate processor. DTS Digital Sound differs from the conventional A-chain in that the audio signal is read from a CD-ROM in a unit separate from the projector and decoded in a DTS processor. See B-Chain.

A/B Or A-B
The direct evaluation of two audio/ video components or systems under identical conditions. The term “A/B - A-B” denotes direct switching from one source to another, enabling a comparison to be made with minimal variability or bias.

Analog-To-Digital Converter. A device which converts an analog value to a digital value.

Industry term for audio/visual or audio/video. Pertains to any display or device that handles sound and video.

A/V Loop
An audio/video input on an A/V receiver or A/V preamplifier that includes both audio and video jacks.

Absolute Black Level
In the original black and white American TV system, absolute black level in a video signal was 0 volts DC. Some 0.285 volts, or 40 IRE, (units of video defined by the Institute of Radio Engineers, 140 IRE = 1 volt, 100 IRE above 0 volts, 40 IRE below 0 volts) of the total 1 volt video signal exists below that black level (now known as blanking level). The -40 IRE will completely shut off the electron beam during the horizontal and vertical retrace intervals. When color came to NTSC in 1953, the level of picture black was raised to +7.5 IRE. The higher level of black was necessary because early black and white transmitters couldn’t handle a color signal with black level at 0 volts. The NTSC system still places black level at +7.5 IRE. Japan abandoned the +7.5 IRE of NTSC in 1990. When high definition arrives, there is a possibility that these levels will change slightly. Synchronization signals will be 0.3 volts and active video will be 0.7 volts. Future TV sets will have to have individual memories for each type of input as do current generations of most data and graphics grade projectors.

Absolute Phase
Correct polarity (direction of energy) over two or more channels.

The dissipation of sound energy into another form of energy-usually heat. When a sound wave encounters resistance, such as that provided by a wall or other obstacle, absorption occurs. Absorption is measured in sabins (after Wallace Clement Sabine). Sabin is the amount of absorption offered by one square foot of open air. For our metric friends, one square meter of absorption is called a metric sabin.

Absorption Co-Efficient
The portion of energy absorbed when a sound wave strikes a material. The absorption coefficient of a material is dependent on the frequency of the sound wave. An absorption co-efficient of 1.0 = total absorption, 0.0 = total reflection. These co-efficents are used to rate acoustic materials' capabilities.

Alternating Current. Flow of electrons that periodically changes direction alternately. The rate of change is known as frequency and is measured in Hertz (cycles per second). Standard wall outlets supply alternating current.

AC Coupled
Circuit does not pass DC component of signal, and it ignores DC offsets.

AC Line Conditioner/Protector
A device that filters noise from the AC powerline and isolates equipment from voltage spikes and surges

A data compression method developed by Dolby Laboratories (also known as Dolby® Digital) that folds six channels of audio into a single digital bitstream. The nominal bit rate for six (5.1) channels is 384 kilobits per second (Kbps), which represents a compression ratio of about 10 to 1, but is capable of a maximum of 448 Kbps. AC-3 is a “lossy” compression scheme. See Dolby® AC-3® and Lossy Compression.

Alternating Current/Direct Current. Switch enables product operation from either AC line power or battery (DC).

Academy Curve
The standard frequency spectrum set in 1938 for monaural film sound reproduction in theatres. Because of the substantial noise levels inherent in optical soundtracks, an extreme rolloff was applied to the high frequencies; at 8 kHz there was already a -15dB attenuation. There was also a rolloff in the low end, starting from 125Hz, to prevent a “boominess” characteristic in theatrical sound systems of the day. The Academy curve would remain as the standard for decades to come, until the advent of Dolby Stereo in the 1970s.

Automatic Color Control. Maintains constant color (chroma) signal levels. The burst signal is used as the ACC reference. Should be defeated if an accurate picture is desired.

Completely colorless white light.

Acoustic Absorber
Any material that absorbs sound.

Acoustic Engineer
See Acoustic Consultant List.

Acoustical Tile
A porous architectural material, usually constructed from fiberglass or pressed particle board which is highly absorptive at the high frequencies (over 1,000 Hz).

The science of sound and sonic transmission or sound behavior. The study of the behavior of sound waves in a finite space that acoustically differentiates one environment from another, such as a living room from a concert hall. The characteristics of a room in respect to the transmission of sound—such as how sound is reflected and absorbed. Active Crossover — A crossover designed as an electronic device in audio components or by itself that divides the signal from a source component into frequency bands. The term “active” means that the crossover is powered.

Active Lines
Only those video or horizontal scanning lines that carry visible picture information, as opposed to blanking lines and vertical sync lines.

Active Matrix LCD
A type of liquid crystal display in which each pixel (picture element) is individually connected to a power transistor and can be individually turned on or off.

Active Subwoofer
A loudspeaker designed only to reproduce low frequencies that includes an integral power amplifier to drive the loudspeaker.

Analog Distribution Amplifier. A device that takes in one signal and distributes it to several outputs without “tying” those outputs together (buffered).

A linking device which allows two dissimilar devices to connect physically, and/or communicate electronically. An interface between two sources

Analog-To-Digital Converter. A circuit that converts an analog (varying amplitude) signal to a digital (pulse type) signal. See Analog-To-Digital Converte

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 percent, produce white on a video screen; absence of all three produce black. See Subtractive Color (CYMK)

Additive Primary
One of the three red, green, and blue colors that are the basis of all hues when light is mixed against a black background.

Adjacent Channel
A television channel located next to another channel in the frequency spectrum.

Automated Dialogue Replacement. Also known as looping. An important step in film sound post-production where the actors in a movie re-record their words while watching the film to make sure that wording and lip movements are in sync. ADR is needed because dialogue recorded on the set or on location is often muffled and competing with other noises encountered during production.

Advanced Definition Television. An early version of high definition television (HDTV) devised in Japan. Now superseded by US HDTV standards.

Abbreviation for Audio Engineering Society.

AES/EBU Interface
The professional standard, established by the Audio Engineering Society (AES) and the European Broadcasting Union (EBU) for digital audio signal transmission between components. Equipment using the AES/EBU interface in professional applications use balanced XLR connections.

Automatic Frequency Control. Circuit that locks TV or FM receiver to station frequency.

Automatic Fine Tuning. — A circuit that compensates for a change in frequency due to tuner oscillator drift.

Automatic Gain Control. Automatic gain can be applied ahead of almost any circuit that requires specific levels to operate. As an example, the color decoder needs to see a particular level of color sub-carrier at its input in order to display the correct color at the output. There is a reference burst at the beginning of each horizontal line of known original amplitude. The AGC circuit looks at the incoming signal level and applies any gain correction necessary to make the burst amplitude correct. In the process of doing that, it also corrects the amplitude of the color information in the active picture area.

Air Coupled Lens
A basic type of coupling between the CRT and lens. The air coupled lens greater adjustment range than liquid coupled lenses. See Liquid Coupled Lens.

Automatic Level Control. Also called Automatic Gain Control (AGC), and Automatic Volume Control (AVC). In audio recording, a circuit used to control the output level automatically, without distortion due to overload.

See Flicker.

Alternate Scanning
An imaging technique in which the picture is drawn by two interlaced field scans rather than by a single sequential scan (progressive scan). Unless line-doubled, all NTSC images are formed this way. See Interlaced.

Amplitude Modulation. A method of radio transmission, by which the information part of the signal causes the amplitude to vary (modulate) without affecting the frequency. Used in standard radio broadcast band from 530 to 1705 kHz.

Low level sounds that set an atmospheristic mood or suggest the spatial character of a particular place. The mood created by a room and its contents.

1) The residual “room sound” or acoustics of a listening environment defined by attributes such as spatial dimensions, reverberation, echoes, reflections and background noise. Movie soundtracks can sometimes recreate ambience by imparting a spatial characteristic in the surround channel. Ambience also can be synthesized by some digital surround processors. In classical music, for example, the term ambience is used interchangeably with the word reverberation, to refer to the persistence of decaying sounds in the listening room. (Not to be confused with ambient noise, which refers to background noise.) 2) The subjective determination by an individual of how pleasant a listening space is perceived to be.

Ambient Noise
The average amount of background noise in an environment, measured in decibels (dB). Amplitude The height of a waveform above or below a zero reference line. It refers to fluctuations of air pressure above and below normal atmospheric pressure. This corresponds roughly to loudness. However, the term amplitude can also be used to refer to electrical phenomena, in which case it represents the fluctuations of voltage or current. American National Standards Institute — ANSI. The organization which sets standards for United States A/V equipment.

Without definite form or shape; not crystallized.

Ampere. The international base unit of electric current. Symbolized by “A.” One (1) amp is equal to the steady current produced by 1 volt applied across a resistance of 1 ohm.

See Amp.

A device, either by itself (power amplifier) or used in a component (integrated amplifier or receiver) which increases the amplitude of the voltage signal input to it and provides that powered original signal as an output.

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 in volts or decibels.

Amplitude Modulation
See AM.

Or Analogue. A continuous action, or movement that takes time to change from one position to another. The representation of audio as a time-varying voltage signal whose waveform is a direct representation of the sound. Standard audio and video signals are analog. An analog signal has an infinite number of levels between its highest and lowest value. (Not like digital, where changes are by steps, “on” or “off,” or binary ones and zeros) The storage of analog signals is accomplished by various means, such as magnetic, optical (for films), and frequency modulation (FM, used on LaserDiscs and VHS-HiFi).

Analog Control
A method using continuously varying voltage levels to provide control of equipment.

Analog Recording
A method of recording and encoding information by use of a continuously varying signal, rather than dis crete (digital) pulses.

Analog-To-Digital Converter
ADC. A device used to convert analog signals (varying amplitude) to digital (pulse type) signals. See ADC.

A type of lens or adapter designed to produce a widescreen image from a condensed image on the film. Trademarks are CinemaScope®, Panavision® and VistaVision®.

Anamorphic Widescreen Video
Vertical resolution improves when the anamorphic method of widescreen presentation is employed. This is where the horizontal dimension is squeezed so that more of the vertical space can be used. The squeeze ratio is 1.78 to 1.33, since that is what has been used in Europe and Japan for a number of years now. Anamorphic video is horizontally squeezing a widescreen image into a 1.33:1 image. How wide? A 1.78:1 image is captured, whether it’s a letterboxed 2.35:1 or 1.85:1 image, and squeezed into a 1.33:1 image area. The objects are squeezed, and they look tall and thin if played back on a regular TV set. DVD players and special widescreen sets can unsqueeze these images, restoring them back to their 1.78:1 image. The advantage of the anamorphic format is 33 percent more vertical detail in widescreen images over the letterboxed image. The DVD format is an anamorphic widescreen capable format. A 1.78:1 anamorphic film original image on DVD has a potential of 640 vertical lines (or 360 horizontal transitions per picture height) and 480 horizontal lines. In addition there is far better color resolution capability on this format than on a LaserDisc.

An extremely dead acoustical condition in which reverberation is non-existent. Specially designed rooms called anechoic chambers lacking any acoustical signature have been developed for critical audio testing and measurement.

Anechoic Chamber
A specially designed room in which all sound reflections are absorbed and reverberation does not exist. Such spaces are utilized extensively for the testing of microphones, loudspeakers and other audio equipment.

Anechoic Recording
Generally an instrumental recording lacking all acoustic signature. Often used for auralization processing.

Angle Of Incidence
The angle formed by a ray incident on a surface and a perpendicular to the surface at the point of incidence.

Angle Of Reflection
The angle formed by a reflected ray and a perpendicular to the surface at the point of reflection.

Angular Reflective Screen Surface
The light output of this type of screen is reflected off the surface at the same angle it hits the screen. In other words, if light comes in from a high angle, as it would from a ceiling mounted projector, it will be reflected at an equal angle below the center line of the screen, in the direction of the audience. Within the category of Angular Reflective screens, there are many sub-types, independent of the gain of the screen. There are “Silver” screens, as an example, that are needed in 3-D video polarized light applications. Regular Angular Reflective video screens use variations of the matte white material. The grain size of elements on the surface of the matte screen are kept small enough to be far below the resolution of the picture being reflected off the screen. With curved and flat Angular Reflective screens picture quality varies depending on the viewing position.

American National Standards Institute. The organization which sets standards for United States A/V equipment. In 1992 ANSI helped establish and promulgate a series of measurement specifications which were intended to evaluate the actual viewable image which emanates from large screen display devices.

ANSI Lumens
Away of measuring brightness. The display is divided into nine rectangles each of which measures “of screen Height” by “of screen Width.” A brightness reading is taken at the center of each rectangle and then the average of the nine readings in lux (lux = lumen/square meter) shall be multiplied by the number of square meters of the image at the plane of the meter reading. The result is the light output specification of the projector in lumens. See Lumens.

The orifice, usually an adjustable iris, which 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 screen-like feature of Sony Trinitron monitors and others licensed by Sony which controls the number of electrons hitting the phosphor coating on the screen. Also called “slot mask.”

Aperture Ratio
The amount of useful picture information on the screen.

A quantitative measure of the intelligibility of speech. How well the listener understands what the speaker is saying

Visible (or audible) consequences of various video processes considered to be aesthetic flaws.

American Standard Code for Information Interchange. The standard code consisting of 7-bit coded characters (8 bits including parity check), utilized 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 a rectangle. In viewing screens, standard TV is 4:3, or 1.33:1 (similar to the Academy standard for films before the 1950’s); HDTV is 16:9, or 1.78:1. Sometimes the “:1” is implicit making TV = 1.33 and HDTV = 1.78. The aspect ratio of standard flat spherical films is 1:85, Anamorphic Scope 2:35 (or 2:40:1), and 65mm (70mm) from 2:05:1 to 2:21:1.

Aspect Ratio
None specified.

Aspect Ratio Accommodation
Techniques in which something shot in one aspect ratio can be presented in another.

Low level background sounds, such as wind or traffic noise, which add to the reality of a motion picture scene. These sounds are sometimes recorded separately a the scene’s location or other locations, creating what is called a wild track for mixing into the soundtrack later. See Ambiance

Adaptive Transform Acoustic Coding. A scheme developed by Sony to allow several channels of digital audio to form a single low-rate bitstream. Similar to Dolby’s AC-3®, it utilizes data reduction and compression schemes based on perceptual coding techniques. Low bit rate ATRAC is used in the Sony Dynamic Digital Sound (SDDS) theatrical format, as well as the Sony MiniDisc (MD), but at a higher bit rate (384 kilobits per second) for two-channel stereo.

Advanced Television Systems Committee. The industry-led federal advisory committee selecting a new Advanced TV standard for the United States. The voluntary ATSC DTV Standard was adopted December 24, 1996 except for the video format “constraints” described in ATSC Table III. See ATSC’s web site: and ATSC Table III Formats.

ATSC Table III Formats
HDTV formats: 1) 1080x1920 pixels 16:9, 2) 720x1280 pixels 16:9. SDTV formats: 480x704 pixels 16:9, 4) 480x704 pixels 4:3, 5) 480x640 pixels 4:3. The other variables in the scanning formats are the scanning technque, either Interlaced (I) or Progressive (P) and the frame rate. Under 1080x1920 there are three combinations: 1) 60I, 30P and 24P. Under 720x1280 three are three combinations: 1) 60P, 30P and 24P. Under 480x704 16:9 there are four combinations :60P, 60I, 30P and 24P. Under 480x704 4:3 there are four combinations: 60P, 60I, 30P and 24P. Under 480x640 there are four combinations: 60P, 60I, 30P and 24P.

Advanced Television Test Center. Created to test proposed Advanced TV systems with federal oversight and industry participation.

To reduce the level of an electrical or acoustical signal.

To reduce the amplitude (strength) of a signal or current.

Advanced TeleVision. Set of TV standards for high-definition TV (HDTV), enhanced-definition TV (EDTV—lower resolution than HDTV), IDTV (NTSC TV with line doubling), and advanced digital 525-line or better resolution. See Grand Alliance.

Of or concerning sound, specifically the electrical currents representing a sound program or the sound portion of an A/V program

None specified except usable audio.

Audio (Inputs/Outputs-Pairs)
The number indicates the number of inputs and the number of outputs on TV sets. Audio I/Os are listed in pairs. Normally there are more audio outputs than video ones.

Audio Dub
To re-record the audio portion of a videotape without disturbing the video portion. To copy an audio tape.

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
An acoustical or electrical signal of a frequency that falls within the audible range of the human ear, usually recognized as a bandwidth of 20 Hz to 20 kHz. See Audio Spectrum.

Audio Frequency
An acoustical or electrical signal of a frequency that falls within the audible range of the human ear, usually recognized as a bandwidth of 20 Hz to 20 kHz. See Audio Spectrum.

Audio Spectrum
The full range of audio frequencies from the lowest to the highest. The audio spectrum that humans can hear ranges from 20 Hz to 20 KHz, though deep bass below 20 Hz can be felt.

Audio/Video Receiver
An all-in-one hub of an audio/video system. See Receiver.

The process where predicted octave-band echograms are converted to binaural impulse responses that can be convolved with anechoically recorded music simulating an impression of how the music would sound in the modeled space. It involves digital signal processing and Head-Related Transfer Functions (HRTFs). In addition to binaural responses, directive microphone, stereo, and B-format responses can be created. Basically, the ability to determine how a room will sound (within certain substantive limits of accuracy which vary from process to process) from a design before the room is actually built.

Auto Tune Or Auto Program
A TV’s ability to automatically tune or program stations that are used by broadcasters and skip those left unused.

Automatic focus. A device in a projector or camera which uses light reflected from a surface to focus the image.

Automatic picture sizing adjustment to compensate for different display modes, then enabling the display system to center the picture and fill the screen.

In equipment that has loop-through, or “daisy-chain” connections, termination is done at the last device on the chain. Some such devices provide termination automatically by the fact that there is no cable going out. Thus, this is the last device and termination is provided.

Automatic Convergence
The automatic alignment of the red, green and blue color images.

Automatic Gain Control
1) In video, the AGC adjusts the gain of the entire color signal until the burst amplitude is correct. This circuit is an absolute necessity on all consumer display devices. 2) In audio recording, a circuit used to automatically control the volume of the recorded signal without distortion due to overload. An AGC-defeat control permits manual volume control for wide ranges and other special recording purposes. Sometimes called automatic level control (ALC), or automatic volume control (AVC).

Automatic Level Control
ALC. 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). An ALC defeat control permits manual level control for wide ranges or special recording purposes.

Auxiliary. A nonspecific line input to a control unit or pre-amplifier.

Average Picture Level
APL. The overall average luminance level for the image.

American Wire Gauge. A standard measurement for wire conductor diameter

Axial Mode
The room resonances associated with each pair of parallel walls.

An imaginary line that is perpendicular to the front of the microphone diaphragm. Those sounds reaching the microphone at an angle to the axis are said to be off-axis. This can also be applied to loudspeakers.