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5.1 Surround Sound - The digital audio multichannel format developed by the Moving Picture Experts. IT refers to the five discrete, full bandwidth (20-20kHz) channels - left, right, & center fronts, plus left & right surrounds - and the ".1" usually refers to the limited bandwidth (20-120Hz) subwoofer channel.

A -

AC-3 (audio coding 3)- Dolby's digital audio data compression algorithm adopted for HDTV transmission and used in DVDs, laserdiscs and CDs for multichannel home theater use. Also see: Dolby Digital

Acoustics- The science or study of sound.

Ambient Noise- The sound that exists in a room that does not come from a loudspeaker, musical instrument or some other intentional sound source. A person speaking to an audience is not ambient noise, etc.

Amplifier- A device which increases signal level. Many types of amplifiers are used in audio systems. Amplifiers typically increase voltage, current or both.

Aspect Ratio- Ratio of a picture's width to its height. Typical television aspect ratio is 4:3, while wide screen formats provide greater width of the viewing area.

Audio frequency- The acoustic spectrum of human hearing, generally regarded to be between 20 Hz and 20 kHz.

B -

Bandwidth- The range of frequencies reproduced by an amplifier or transducer.

Bipolar- Type of loudspeaker with drivers mounted on opposite sides of the cabinet, or speaker enclosure. Drivers move in and out together so they remain "in-phase." Used as rear-surround speakers; better when placed closer to the listener. (Also see dipolar)

C -

Coax- Short for Coaxial cable - a type of 75 ohm cable most commonly used for Cable TV connections and with some antenna systems for FM radio and Television. Also used to connect CD or DVD transports to DACs. May also be found as the basis for many video interconnect cables including composite, s-video, component, and RGB.

Component video- A video signal transfer method utilizing three cables which separate the three parts of a video signal: Luminance (Y) is the black & white, pR and PB are the separate portions of the Chrominance, or color signal. Component Video, properly implemented, should provide the best possible image quality on TV monitors that support it.

D -

DAC- A Digital to Audio Converter. Converts a digital bitstream to an analog signal. Can be a separate "box" that connects between a CD Transport or CD Player and a pre-amplifier.

Damping- The reduction of movement of a speaker cone, due either to the electromechanical characteristics of the speaker driver and suspension, the effects of frictional losses inside a speaker enclosure, and/or by electrical means.

Decibel- Essential acoustics measurement; a unit of sound used to measure the relative differences between sounds. Equal to one-tenth of a bel, the amount of energy in the form of sound that is transmitted to one square centimeter of the ear. One dB is considered to be the smallest change in sound that is perceptible to the human ear.

Distortion- Audio distortion: a measure of unwanted signals; the name given to anything that alters a pure input signal in any way other than changing its size. The most common forms of distortion are unwanted components or artifacts added to the original signal, including random and hum-related noise.

Dolby Digital- A five-channel system consisting of discrete left, center, right and left rear, right rear channels. The AC3 standard also has a separate subwoofer channel for the lowest frequencies.

DTS- Digital Theater Systems ( DTS is an international, digital technology company specializing in multichannel audio for entertainment. DTS Digital Surround is an encode/decode system that delivers six channels (5.1) of master-quality, 20-bit audio

DTV- Digital TV. A new system of digital television broadcasts.

DVD- Originally coined as Digital Video Disc or then changed to Digital Versatile Disc, upon adoption by the computer industry. DVD has the same physical dimensions of a CD, however it can hold much more information.

E -

Efficiency- The loudspeaker parameter that gives the level of sound output when measured at a prescribed distance with a standard level of electrical energy fed into the speaker. Often expressed as decibels/watt/meter (dB/w/m).

EQ (Equalizer)- Electronic device that acts as active filters used to boost or attenuate certain frequencies.

H -

HDTV- The highest rung in the ladder of various DTV formats. Three determining factors delineate HDTV: 1080 active scan lines, 16:9 widescreen ratio, and Dolby Digital sound.

Home Theater In A Box (HTiB)- Any of several kinds of packaged audio-for-video systems designed to create an "instant" home theater; usually inexpensive and compact. Typically includes a multi-speaker complement plus a receiver or multichannel amplifier to drive the speakers. May function as a stand-alone 5.1-channel system or may be designed to add channels to an existing stereo or other audio system.

I -

Imaging- the speaker's ability to localize different instruments playing simultaneously.

In-Wall Speakers- Speakers designed to mount flush within a wall.

M -

Magnetically Shielded- A type of loudspeaker in which the electromagnetic field created by the driver magnets - which can discolor a TV picture and potentially ruin a tube - is contained.

Midrange- The mid band of an audible signal, typically anywhere between 350 Hz and 3 kHz. Also refers to those specific frequencies as well.

N -

NTSC- National Television System Committee. The NTSC standard has a fixed vertical resolution of 525 horizontal lines. There are 60 fields displayed per second. A field is a set of even lines, or odd lines. The odd and even fields are displayed sequentially, thus interlacing the full frame. One full frame, therefore, is made of two interlaced fields, and is displayed about every 1/30 of a second. See also interlaced.

R -

RCA Connector- Standard pin plug or jack used to connect audio and video components, developed by RCA Laboratories. Also known as a phono plug or jack, even when applied to non-phono equipment.

S -

Soundstage- Listening term. Perceived width, depth, and height of music (or sound) especially for stereo reproduction. A set of speakers with good soundstaging means you can localize a separate position for each instrument and voice, emulating a live performance.

Stereo- Derived from the Greek word meaning solid. Two channel audio format. However, the purpose of stereo is not to give you separate right and left channels, but to provide the illusion of a three-dimensional, holographic image between the speakers.

Subwoofer- A speaker designed exclusively for low-frequency reproduction. A true subwoofer should be able to at least reach into the bottom octave (20-40Hz). They are usually contained in their own enclosure and can be placed anywhere in a listening room due to the fact that low frequencies cannot be localized or pinpointed.

S-VHS- Super VHS. A recording and playback format requiring an SVHS VCR. As the name implies, it's better than standard VHS, producing about 480 lines of resolution. (Standard VHS displays about 240 lines.)

T -

THX- Tomlinson Holman Experiment. THX is a set of technical standards and performance criteria developed by Lucasfilm to ensure that moviegoers see and hear a film at optimum performance levels, "as the director intended". This comprehensive set of standards includes rigorous specifications designed to optimize equipment, room acoustics, background noise levels, and projection and viewing angles.

Tweeter- Transducer responsible for reproducing the higher frequencies of an audible signal, typically active above 3 or 4 kHz.

W -

Watt- A unit of electrical power. A watt of electrical power is the use of one joule of energy per second. Watts of electrical power equals volts times amperes.

Widescreen- In home theater, a viewing aspect ratio wider than 4:3 (which is the typical television ratio). There are various widescreen formats, one of which is 16:9.

Y -

Y-adapter- Any type of connection that splits a signal into two parts. An example would be a connector with one female RCA jack on one end, and two male RCA jacks on the other end.