Extron Glossary of Terms

A/D - Analog to Digital (converter). A device that converts an analog signal to a digital value.

A/V - Audio visual, or audio video.

AAP - Architectural Adapter Plate. Mountable metal plates that provide active and pass-through connectors and control modules to maintain a clean and efficient A/V system design.

AC - Alternating Current. Electron flow that changes direction alternately.

AC coupled - When a circuit does not pass the DC component of a signal, and it ignores DC offsets.

Achromatic - Completely colorless white light.

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.

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

Adapter - A linking device that allows two dissimilar devices to connect physically, and/or communicate electronically, such as VGA to Mac adapter.

ADC - Analog to Digital Converter. A device that converts analog signals to digital signals.

ADC - Apple Display Connector. Common to current Apple displays, non-LCD and LCD alike. One connection routes all power, USB, and digital video signal to the monitor on a single cable.

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 (CMYK)."

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 Now superseded by US HDTV standards.

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.

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).

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 "

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.

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.

American Standard Code for Information Interchange - American Standard Code for Information Interchange. It is 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.

Amorphous - (1) Without definite form or shape; not crystallized. (2) An early type of LCD panel technology before polysilicon.

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.

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 recording - A method of recording and encoding information by use of a continuously varying signal, rather than by discrete (digital) pulses.

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.

ANSI - See American National Standards Institute.

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. See "Lumen."

Antialiasing - 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. 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 - 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.

AR - Extron's abbreviation for Analog/Remote. Indicating that the device will pass analog signals and it has remote control. Alternatively, analog RGB.

ARP - 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 - Artifacts — Visible corruption of the image or undesirable elements or defects in a video picture. These may occur naturally in the video process but must be eliminated to produce a high quality picture.

ASCII - 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 - 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 - 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 - 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 - ATM — Asynchronous Transfer Mode. In videoconferencing, a system for transmission and switching of digital signals through the telephone system. See "Asynchronous."

ATSC - 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 - Attenuate/Attenuation — To reduce the amplitude (strength) or current of a signal.

Audio - Of or concerning the electronic transmission of sound, specifically the electrical currents representing a sound. (CF. Sound)

Audio dub - To re-record the audio portion of a videotape without disturbing the video portion. To copy audio from one tape to another.

Audio follow - 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 - Audio frequency — Frequencies within the range of human hearing, about 20 Hz to 20 kHz.

Audio summing amplifier - 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-termination - 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 having no cable going out, thus indicating that this is the last device and termination is provided.

Autofocus - Auto-focus — Automatic focus. A device in a projector or camera that uses light reflected from a surface to focus the image.

AutoImage™ - 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.

Automatic convergence - The automatic alignment of the red, green, and blue color images on a screen.

Automatic gain control - 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. It is 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.

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).

Autosequencing - A switcher feature that causes the switcher to automatically select each one of its channels in succession, repeatedly sequencing through all channels.

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.

AWG - American Wire Gauge. A standard measurement for wire conductor diameter.