A/B comparison A back-and-forth listening comparison between two audio or video presentations, A and B.

AC line-conditioner/protector A device that filters noise from the AC powerline and isolates equipment from voltage spikes and surges. Some AC line-conditioners/protectors also protect equipment from lightning strikes. Home-theater equipment is plugged into the AC line-conditioner/protector, and the conditioner is plugged into the wall.

acoustic absorber Any material that absorbs sound, such as carpet, drapes, and thickly upholstered furniture.

acoustic diffuser Any material that scatters sound.

acoustics The science of sound behavior. Also refers to a room; i.e.,“This room has good acoustics.”

AC-3 The encoding format used to create Dolby Digital, the 5.1-channel discrete digital surround-sound format; see “Dolby Digital.”

active subwoofer A speaker designed to reproduce only low frequencies and that includes an integral power amplifier to drive the speaker.

ADC See “analog-to-digital converter.”

adjacent-channel selectivity Tuner specification that describes a tuner’s ability to reject radio stations adjacent to the desired station.

Advanced Television System Committee (ATSC) Group that set the terrestrial transmission and format standards for digital television. Also, the transmitted signals that follow that format.

alternate-channel selectivity Tuner specification describing a tuner’s ability to reject stations two channels away from the desired station.

ambience Spatial aspects of a film soundtrack that create a sense of size and atmosphere, usually reproduced by the surround speakers.

ampere Unit of electrical current, abbreviated A.

analog An analog signal is one in which the varying voltage is an analog of the acoustical waveform; i.e., it is continuously variable. Contrasted with a digital signal, in which binary ones and zeros represent audio or video information.

analog-to-digital converter (A/D, ADC) A circuit that converts an analog signal to a digital signal.

anamorphic A film or video format in which a widescreen image has been “squeezed” horizontally (either with lenses or by digital manipulation) to fit a standard 4:3 aspect ratio. Correct picture geometry is restored on play-back by “unsqueezing” the image into its original aspect ratio. The anamorphic format delivers the correct aspect ratio without sacrificing resolution. Anamorphic DVDs may carry the legend “Anamorphic Widescreen,” “16:9 Enhanced” or “Enhanced for Widescreen Televisions.”

ANSI lumens Measurement of a video display’s light output, or the light output from a front projector as reflected from a projection screen.

aspect ratio The width-to-height ratio of a visual image. Standard television sets have an aspect ratio of 4:3 (1.33:1). Widescreen television sets have an aspect ratio of 16:9 (1.78:1).

aspect-ratio control A feature in some HD-ready televisions that allows you to manually adjust the aspect ratio.

atmosphere See “ambience.”

ATSC See “Advanced Television System Committee.”

A/V Short for audio/video. Identifies a component or system as one that processes video as well as audio signals.

AV/C Audio-Video Control, a simple FireWire-based technology for controlling the components in a home-theater system as a single unit with one remote control.

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

A/V loop An A/V input and A/V output pair found on all A/V receivers and controllers. Used to connect a component that records as well as plays back audio and video signals. A DVD recorder is connected to a receiver’s or controller’s A/V loop.

A/V preamplifier Also called by its more descriptive name of an “A/V controller,” the A/V preamplifier is a component that performs surround decoding and lets you control the play-back volume and select which source you want to watch and listen to.

A/V preamplifier/tuner An A/V preamplifier that includes, in the same chassis, an AM and/or FM tuner for receiving radio broadcasts.

A/V receiver The central component of a home-theater system; receives signals from source components, selects which signal you watch and listen to, controls the playback volume, performs surround decoding, receives radio broadcasts, and amplifies signals to drive a home-theater loudspeaker system. Also called a “surround receiver.”