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Visual Audio Professional Glossary

2018-02-08 10:52 admin 人关注
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A/D - Analog to Digital (converter). A device that converts an analog signal to a digital value.
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. The ICT – Image Constraint Token is a provision within AACS that allows the content provider to limit analog output resolutions.
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 critical angle, 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 - 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."
Adobe RGB - A color space specification developed by Adobe® Systems, Inc., offering a wider color gamut than sRGB. Adobe RGB is supported in Photoshop® and other Adobe software, as well as some digital cameras, printers, scanners, and displays.
ADSL - Asymmetrical Digital Subscriber Line. One of a number of DSL technologies, and the most common one. ADSL is designed to deliver more bandwidth downstream (from the central office to the customer site) than upstream.
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, LLP, 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 - 3-conductor, 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 moiré 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.
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.
Ambient Sound List - 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 - When used colloquially, may refer to the general trend of digital video technologies displacing analog, such as when US broadcast television switched to digital transmission, or the increasing use of DVI, HDMI, and DisplayPort video on PCs instead of RGB, etc. In a narrowly defined legal sense, the analog sunset refers to AACS licensing restrictions placed on Blu-ray Disc players where licensed players produced after 2010 must limit analog video output to standard definition, and licensed players produced after 2013 must not output any analog video, when playing protected content.
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 singlemode 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. APC connectors are typically green in color and are not used in multimode applications. They are also rarely used in digital applications. APC polished connectors are not compatible with UPC, SPC, or PC polished connectors. Intermixing APC polished connectors with UPC/SPC/PC polished connectors can damage the fiber optic cable or equipment.
Animations - Animations consist of motion image sequences produced synthetically on video processing or computing systems.
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. Also 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. Also 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 - Any error in the perception or representation of any visual or aural information introduced by the involved equipment. Image artifacts appear as deviations from the original in the delivered image in video streaming systems.
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. A standardized digital data transmission technology that is a cell-based switching technique which uses asynchronous time division multiplexing. This is the core protocol used over the SONET/SDH backbone of the ISDN (Integrated Services Digital Network).
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.
Auto-Image™ - 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.
AV - Audio visual, or audio video.
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.

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