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Absorption: Reduction of acoustical energy usually by converting it into heat via friction using soft, fibrous materials.

AC3: Audio Codec 3. This was the original and more technical name for Dolby Digital. Replaced by marketing mavens when they realized that Dolby's name was not in the title. Some RF modulated, 5.1-encoded laser discs were labeled as AC3. Later versions were labeled as Dolby Digital.

Academy Curve: An intentional roll-off in a theatrical system's playback response above ~2kHz (to -18dB at 8kHz) to minimize noise in mono optical tracks. Some (many) transfers to home video of mono movies have neglected to add the Academy filter during transfer, giving many old movies a screechy sound they were never intended to have. A few home processors have an Academy filter option, making them a must for old-movie buffs. Has been used since 1938.

Acoustic Suspension: A sealed speaker enclosure that uses the air trapped in the cabinet as a reinforcing spring to help control the motion of the woofer(s).

Active: Powered. An active cross-over is electrically powered and divides the line-level signal prior to amplification. An active speaker includes an active crossover and built-in amplifier.

Amplifier: A component that increases the gain or level of an audio signal.

AM: Amplitude modulated.

Anamorphic: Process that horizontally condenses (squeezes) a 16:9 image into a 4:3 space, preserving 25 percent more vertical resolution than letterboxing into the 4:3 space. For the signal to appear with correct geometry, the display must either horizontally expand or vertically squish the image. Used on about two or three promotional laser discs and many DVDs. Also called Enhanced for Widescreen or Enhanced for 16:9.

Aspect Ratio: The ratio of image width to image height. Common motion-picture ratios are 1.85:1 and 2.35:1. Television screens are usually 1.33:1 (also known as 4:3), which is similar to the Academy standard for films in the '50s. HDTV is 1.78:1, or 16:9. When widescreen movies (films with aspect ratios wider than 1.33:1) are displayed on 1.33:1 televisions, the image must be letterboxed, anamorphically squeezed, or panned-and-scanned to fit the screen.

ATSC: Advanced Television Systems Committee. Government-directed committee that developed our digital television transmission system.

Attenuate: To turn down, reduce, decrease the level of; the opposite of boost.

A-Weighting: Measurement based roughly on the uneven frequency sensitivity of the human ear. The influences of low and high frequencies are reduced in comparison to midrange frequencies because people are most sensitive to midrange sounds.

Balanced Input: A connection with three conductors: two identical signal conductors that are 180 degrees out of phase with each other, and one ground. This type of connection is very resistant to line noise.

Bandpass: A two-part filter that cuts both higher and lower frequencies around a center band. A bandpass enclosure cuts high frequencies by acoustic cancellation and low frequencies by natural physical limitations on bass response.

Bandwidth: In audio, the range of frequencies a device operates within. In video, the range of frequencies passed from the input to the output.

Bass: Low frequencies; those below approximately 200 Hz.

Bass Reflex: See Port.

Bipolar: 1) The condition of possessing two pole sets. In a conventional (non-FET) transistor, one pole set exists between the base and collector, and the other pole set exists between the base and emitter. 2) Speakers that consist of two driver arrays facing opposite directions and wired in electrical phase with one another to create a more diffuse soundstage.

Bi-Wiring: A method of connecting an amplifier or receiver to a speaker in which separate wires are run between the amp and the woofer and the amp and the tweeter.

Black Level: Light level of the darker portions of a video image. A black level control sets the light level of the darkest portion of the video signal to match that of the display's black level capability. Black is, of course, the absence of light. Many displays, however, have as much difficulty shutting off the light in the black portions of an image as they do creating light in the brighter portions. CRT-based displays usually have better black levels than DLP, plasma, and LCD, which rank, generally, in that order.

Boost: To increase, make louder or brighter; opposite of attenuate.

Bridging: Combining two channels of an amplifier to make one channel that's more powerful. One channel amplifies the positive portion of an audio signal and the other channel amplifies the negative portion, which are then combined at the output.

Brightness: For video, the overall light level of the entire image. A brightness control makes an image brighter; however, when it is combined with a contrast, or white level control, the brightness control is best used to define the black level of the image (see Black Level). For audio, something referred to as bright has too much treble or high-frequency sound.

Cascading Crossovers: Two crossovers used in series on the same signal in the same frequency range causing greater attenuation of the out-of-band signal. For example, using the crossover in a receiver's bass management setting and the one in a subwoofer simultaneously will create an exaggerated loss of signal.

Cathode Ray Tube: (CRT) Analog display device that generates an image on a layer of phosphors that are driven by an electron gun.

CD: Compact Disc. Ubiquitous digital audio format. Uses 16-bit/44.1-kHz sampling rate PCM digital signal to encode roughly 74 or 80 minutes of two-channel, full-range audio onto a 5-inch disc.

CD-R: Recordable Compact Disc

CD-RW: Rewritable Compact Disc

CEA: Consumer Electronics Association. An association of manufacturers of consumer electronics products.

Center Channel: The center speaker in a home theater setup. Ideally placed within one or two feet above or below the horizontal plane of the left and right speakers and above or below the display device, unless placed behind a perforated screen. Placement is important, as voices and many effects in a multichannel mix come from this speaker.

Channel: In components and systems, a channel is a separate signal path. A four-channel amplifier has at least four separate inputs and four separate outputs.

Chrominance: (C) The color portion of a video signal.

Coaxial: 1) A speaker typically with one driver in the middle of, and on the same axis as, another driver. 2) An audio or video cable with a single center pin that acts as the hot lead and an outer shield that acts as a ground.

Codec: Mathematical algorithms used to compress large data signals into small spaces with minimal perceived loss of information.

Coloration: Any change in the character of sound (such as an overemphasis on certain tones) that reduces naturalness.

Component Video: A signal that's recorded or transmitted in its separate components. Typically refers to Y/Pb/Pr, which consists of three 75-ohm channels: one for luminance information, and two for color. Compared with an S-video signal, a Y/Pb/Pr signal carries more color detail. HDTV, DVD, and DBS are component video sources, though most DBS material is transcoded to component from composite signals.

Compound Loading: See Isobarik.

Composite Video: A signal that contains both chrominance and luminance on the same 75-ohm cable. Used in nearly all consumer video devices. Chrominance is carried in a 3.58-mHz sideband and filtered out by the TV's notch or comb filter. Poor filtering can result in dot crawl, hanging dots, or other image artifacts.

Contrast: Relative difference between the brightest and darkest parts of an image. A contrast control adjusts the peak white level of a display device.

Controller: Generic term that typically refers to a combination preamp/surround processor or receiver. Can also refer to a handheld wireless remote.

Crossover: A component that divides an audio signal into two or more ranges by frequency, sending, for example, low frequencies to one output and high frequencies to another. An active crossover is powered and divides the line-level audio signal prior to amplification. A passive crossover uses no external power supply and may be used either at line level or, more commonly, at speaker level to divide the signal after amplification and send the low frequencies to the woofer and the high frequencies to the tweeter.

Crossover Frequency: The frequency at which an audio signal is divided. 80 Hz is a typical subwoofer crossover point and is the recommended crossover point in theatrical and home THX systems. Frequencies below 80 Hz are sent to the subwoofer; signals above 80 Hz are sent to the main speakers.

Crossover Slope: The rate of attenuation expressed in decibels of change for every octave away from the crossover frequency.

CRT: See Cathode Ray Tube.

Cut: To reduce, lower; opposite of boost.

Damping: Of or pertaining to the control of vibration by electrical or mechanical means.

Damping Material: Any material that absorbs sound waves and eliminates acoustic energy by converting it into a different form. Fibrous material, for example, turns acoustic energy into heat via friction.

D'Appolito: Vertically symmetrical driver array. Typically consists of a tweeter mounted between two woofers. Creates a more-vertically directional sound with evenly spaced lobes in the off-axis response when compared with asymmetrical driver arrays.

DBS: Direct Broadcast Satellite. Term that replaced DSS to describe small-dish, digital satellite systems such as DirecTV and Dish Network.

Decibel (dB): A logarithmic measurement unit that describes a sound's relative loudness, though it can also be used to describe the relative difference between two power levels. A decibel is one tenth of a Bel. In sound, decibels generally measure a scale from 0 (the threshold of hearing) to 120-140 dB (the threshold of pain). A 3dB difference equates to a doubling of power. A 10dB difference is required to double the subjective volume. A 1dB difference over a broad frequency range is noticeable to most people, while a 0.2dB difference can affect the subjective impression of a sound.

Delay: The time difference between a sonic event and its perception at the listening position (sound traveling through space is delayed according to the distance it travels). People perceive spaciousness by the delay between the arrival of direct and reflected sound (larger spaces cause longer delays).

Diaphragm: The part of a dynamic loudspeaker attached to the voice coil that produces sound. It usually has the shape of a cone or dome.

Diffusion: In audio, the scattering of sound waves, reducing the sense of localization. In video, the scattering of light waves, reducing hot spotting, as in a diffusion screen.

Diffusor: Acoustical treatment device that preserves sound energy by reflecting it evenly in multiple directions, as opposed to a flat surface, which reflects a majority of the sound energy in one direction.

Digital Theater Systems: See DTS.

Digital Audio Server: Essentially a hard drive, a digital audio server stores compressed audio files (like MP3 or WMA). Most include the processing to make the files, and all have the ability to play them back.

D-ILA: Direct Drive Image Light Amplifier. This Hughes/JVC technology uses a reflective LCD to create an image. A light source is then reflected off the reflective LCD and is directed through a lens to a screen.

Dipole: Speakers with drivers on opposite faces that are wired electrically out of phase, creating an area of cancellation to the sides. Recommended by THX for use as surround speakers, with null directed at the listener to create a more ambient and non-localizable effect.

Direct-Stream Digital: A format for encoding high-resolution audio signals. It uses a 1-bit encoder with a sampling rate of 2,822,400 samples per second (verses 44,100 for CD). Used to encode six high-resolution channels on SACD.

Direct-View Television: Display whose image is created on the surface from which it is viewed.

Dispersion: The spread of sound over a wide area.

Distortion: Any undesired change in an audio signal between input and the output.

DLP: Digital Light Processing. A Texas Instruments process of projecting video images using a light source reflecting off of an array of tens of thousands of microscopic mirrors. Each mirror represents a pixel and reflects light toward the lens for white and away from it for black, modulating in between for various shades of gray. Three-chip versions use separate arrays for the red, green, and blue colors. Single-chip arrays use a color-filter wheel that alternates each filter color in front of the mirror array at appropriate intervals.

DMD: Digital Micromirror Device. Texas Instruments engine that powers DLP projectors. Uses an array with tens of thousands of microscopic mirrors that reflect a light source toward or away from the lens, creating an image. Each mirror represents a pixel. See DLP.

DNR: Dynamic Noise Reduction. A signal-processing circuit that attempts to reduce the level of high-frequency noise. Unlike Dolby NR, DNR doesn't require preprocessing during recording.

Dolby B: A noise-reduction system that increases the level of high frequencies during recording and decreases them during playback.

Dolby C: An improvement on Dolby B that provides about twice as much noise reduction.

Dolby Digital: An encoding system that digitally compresses up to 5.1 discrete channels of audio (left front, center, right front, left surround, right surround, and LFE) into a single bitstream, which can be recorded onto a DVD, HDTV broadcast, or other form of digital media. When RF-modulated, it was included on some laser discs, which requires an RF-demodulator before the signal can be decoded. Five channels are full-range; the .1 channel is a band-limited LFE track. A Dolby Digital processor (found in most new receivers, preamps, and some DVD players) can decode this signal back into the 5.1 separate channels. Most films since 1992's Batman Returns have been recorded in a 5.1 digital format, though a number of films before that had 6-channel analog tracks that have been remastered into 5.1.

Dolby EX: An enhancement to Dolby Digital that adds a surround back channel to 5.1 soundtracks. The sixth channel is matrixed from the left and right surround channels. Often referred to as 6.1. Sometimes referred to as 7.1 if the system uses two surround back speakers, even though both speakers reproduce the same signal. Software is backwards-compatible with 5.1 systems, but requires an EX or 6.1 processor to obtain additional benefit.

Dolby Pro Logic: An enhancement of the Dolby Surround decoding process. Pro Logic decoders derive left, center, right, and a mono surround channel from two-channel Dolby Surround–encoded material via matrix techniques.

Dolby Pro Logic II: An enhanced version of Pro Logic. Adds improved decoding for two-channel, non-encoded soundtracks and music.

Dome: A type of speaker-driver shape; usually used for tweeters (convex). Concave domes are usually referred to as "inverted domes."

Dope: A tacky substance added to paper cones to damp spurious vibrations that can cause breakup and rough response. Also, see Editor.

Dot Crawl: An artifact of composite video signals that appears as a moving, zipper-like, vertical border between colors.

Driver: A speaker without an enclosure; also refers to the active element of a speaker system that creates compressions and rarefactions in the air.

DSD: See Direct Stream Digital.

DSP: Digital Signal Processing. Manipulating an audio signal digitally to create various possible effects at the output. Often refers to artificially generated surround effects derived from and applied to two-channel sources.

DTS: Digital Theater Systems. A digital sound recording format, originally developed for theatrical film soundtracks, starting with Jurassic Park. Records 5.1 discrete channels of audio onto a handful of laser discs, CDs, and DVDs. Requires a player with DTS output connected to a DTS processor.

DTS ES: An enhanced version of the 5.1 DTS system. Like Dolby's Surround EX, a sixth channel is added. In some cases (DTS ES Discrete), the sixth channel is discrete. Software is backwards-compatible with 5.1 systems, but requires an ES or 6.1 processor to obtain additional benefit. Neo:6 is a subset of DTS ES that creates 6.1 from material with fewer original channels.

DTV: Digital Television. Umbrella term used for the ATSC system that will eventually replace our NTSC system in 2006. HDTV is a subset of the DTV system. While the FCC does not recognize specific scan rates in the adopted DTV system, typically accepted rates include 480i, 480p, 720p, and 1080i.

D-VHS: Digital VHS. Digital signals recorded onto magnetic tape. Greater capacity than typical VHS; can record compressed HDTV signals. See D-Theater

DVD: Officially known as the Digital Video Disc, though marketers unofficially refer to it as the Digital Versatile Disc. DVD uses a 5-inch disc with anywhere from 4.5 Gb (single layer, single-sided) to 17 Gb storage capacity (double-layer, double sided). It uses MPEG2 compression to encode 720:480p resolution, full-motion video and Dolby Digital to encode 5.1 channels of discrete audio. The disc can also contain PCM, DTS, and MPEG audio soundtracks and numerous other features. An audio-only version, DVD-A uses MLP to encode six channels of 24-bit/96-kHz audio.

DVD-A: Digital Versatile Disc-Audio. Enhanced audio format with up to six channels of high-resolution, 24-bit/96-kHz audio encoded onto a DVD, usually using MLP lossless encoding. Requires a DVD-A player and a controller with 6-channel inputs (or a proprietary digital link) for full compatibility.

DVD-R: A recordable DVD format similar to CD-R in that it is a write-once medium. Backed by Pioneer, Panasonic, Toshiba, and others.

DVD-RW: A recordable DVD format similar to CD-RW in that it is re-recordable medium. Backed by Pioneer, Panasonic, Toshiba, and others.

DVD+R: A recordable DVD format similar to CD-R in that it is a write-once medium. Backed by Sony, Philips, Yamaha, HP, and others.

DVD+RW: A recordable DVD format similar to CD-RW in that it is re-recordable medium. Backed by Sony, Philips, Yamaha, HP, and others.

DVD-RAM: A recordable DVD format similar to DVD-RW in that it is a re-writeable format. Unlike DVD-RW it is capable of being written to and erased over 100,000 times. Backed by Hitachi, Panasonic, Toshiba, and others.

DVI: Digital Visual Interface. Connection standard developed by Intel for connecting computers to digital monitors such as flat panels and DLP projectors. A consumer electronics version, not necessarily compatible with the PC version, is used as a connection standard for HDTV tuners and displays. Transmits an uncompressed digital signal to the display. The latter version uses HDCP copy protection to prevent unauthorized copying. See also HDMI.

Dynamic Range: The difference between the lowest and the highest levels; in audio, it's often expressed in decibels. In video, it's listed as the contrast ratio.

EDTV: Extended Definition Television. This CEA-adopted term (though originally mentioned in an April '99 HT article by Mike Wood and Mike McGann) is defined as those products that can display DTV images as 480p or higher.

Efficiency Rating: Level of sound output measured at a prescribed distance with a standard input power. Efficiency rating standard is 1 watt (2.83V at 8 ohms) at 1 meter over a specified frequency range and is measured in decibels.

Electrostatic: One of the oldest speaker design principles, electrostatic speakers are generally comprised of two fixed perforated panels with a constant high-voltage charge applied to them. In between these two panels is an extremely low-mass diaphragm to which the audio signal is applied, causing it to move. There are variations on this construction, but all electrostatic speakers are free from the magnets and voice coils used in conventional speakers.

Enclosure: The container of air that surrounds the rear of a speaker driver.

Enhanced for 16:9: See Anamorphic.

Enhanced for Widescreen: See Anamorphic.

EQ: See Equalization or Equalizer.

Equalization: Loosely, any type of relative frequency adjustment. Specifically, the process of changing the frequency balance of an electrical signal to alter the acoustical output.

Equalizer: A component designed to alter the frequency balance of an audio signal. Equalizers may be graphic, parametric, or a combination of both.

EX: See Dolby EX.

External Crossover: A standalone unit. See crossover.

Feedback: The transmission of current or voltage from the output of a device back to the input, where it interacts with the input signal to modify operation of the device. Feedback is positive when it's in phase with the input and negative when it's out of phase.

Fiber Optic Cable: Glass, plastic, or hybrid fiber cable that transmits digital signals as light pulses.

FireWire: See IEEE 1394.

FM: Frequency Modulated.

Frequency: The number of cycles (vibrations) per second. In audio, audible frequencies commonly range from 20 to 20,000 cycles per second (Hz). In video, frequency is used to define the image resolution. Low-frequency video images depict large objects or images. Higher frequencies depict smaller objects (finer details).

Frequency Response: A measure of what frequencies can be reproduced and how accurately they are reproduced. A measurement of 20 to 20,000 Hz ± 3dB means those frequencies between 20 and 20,000 Hz can be reproduced no more than 3 dB above or below a reference frequency level.

Full-Range: A speaker designed to reproduce the full range (20 Hz to 20 kHz) of audio frequencies.

Gain: Increase in level or amplitude.

Graphic Equalizer: A type of equalizer with sliding controls that create a pattern representing a graph of the frequency-response changes. Raising sliders boosts the affected frequencies; lowering sliders cuts (attenuates) the affected frequencies.

Gray Scale: The ability for a video display to reproduce a neutral image color with a given input at various levels of intensity.

Hanging Dots: An artifact of composite video signals that appears as a stationary, zipper-like, horizontal border between colors.

HDCP: High-Bandwidth Digital Content Protection. Created by Intel, HDCP is used with HDTV signals over DVI and HDMI connections and on D-Theater D-VHS recordings to prevent unauthorized duplication of copyright material.

HDR: Hard-Drive Recorder. Device that uses a computer hard drive to store compressed digital audio and video signals.

HDMI: HDTV connection format using a DVI interface that transfers uncompressed digital video with HDCP copy protection and multichannel audio.

HDTV: High-Definition Television. The high-resolution subset of our DTV system. The FCC has no official definition for HDTV. The ATSC defines HDTV as a 16:9 image with twice the horizontal and vertical resolution of our existing system, accompanied by 5.1 channels of Dolby Digital audio. The CEA defines HDTV as an image with 720 progressive or 1080 interlaced active (top to bottom) scan lines. 1280:720p and 1920:1080i are typically accepted as high-definition scan rates.

Hi-Fi Stereo: Feature found on VCRs that records or plays back stereo soundtracks with improved fidelity compared to using the linear stereo tracks.

High Gain Screen: Material that reflects more light than a reference material. Increases a projector's light output at the expense of uniformity.

High Pass: A filter that passes high frequencies, and attenuates low frequencies. Same as low cut.

Home Theater in a Box: A complete home theater system in one box (or at least sold together as a package). Consists of five or more speakers, a subwoofer, and a receiver. May also include a DVD player.

Horn: A type of speaker that looks like a horn. These speakers have small drivers and very large mouths; the horn shape serves to transform the small radiating area of the driver into the much larger radiating area of the mouth of the horn.

Hz: Hertz or cycles per second. Something that repeats a cycle once each second moves at a rate of 1 Hz.

IEEE 1394: Networking standard for PCs. Combined with 5C copy protection, is used as a two-way connection to transfer the MPEG-compressed digital bitstreams between consumer electronics items, including HDTV tuners and displays, D-VHS recorders, DVD players, and DBS receivers. Also called FireWire, iLink, …

iLink: See IEEE 1394.

Integrated Amplifier: A combination preamp and amplifier.

Interconnects: Any cable or wire running between two pieces of A/V equipment. For example, RCA terminated cables connecting pre/pros and amps.

Interlace: Process of alternating scan lines to create a complete image. In CRT displays, every second field/frame is scanned between the first field/frame. The first field represents the odd lines; the second field represents the even lines. The fields are aligned and timed so that, with a still image, the human eye blurs the two fields together and sees them as one. Interlace scanning allows only half the lines to be transmitted and presented at any given moment. A 1080i HD signal transmits and displays only 540 lines per 60th of a second. 480i NTSC transmits and displays only 240 lines per 60th of a second. Motion in the image can make the fields noticeable. Interlaced images have motion artifacts when two fields don't match to create the complete frame, often most noticeable in film-based material.

Inverted Dome: A type of speaker-driver shape; usually used for tweeters (concave).

Imaging: The ability to localize the individual sound sources in three-dimensional space.

Impedance: A measure of the impediment to the flow of alternating current, measured in ohms at a given frequency. Larger numbers mean higher resistance to current flow.

Isobarik: Also known as compound loading. By using two low frequency drivers (generally mounted face-to-face and wired electrically out-of-phase or mounted front-to-back in a shallow tube and wired electrically in phase) you can halve the volume of the cabinet without reducing the low frequency extension of the subwoofer.

Keystone: A form of video image distortion in which the top of the picture is wider than the bottom, or the left is taller than the right, or vice versa. The image is shaped like a trapezoid rather than a rectangle.

kHz: Kilohertz or one thousand Hz.

Laser Disc: Now-defunct 12-inch disc format with excellent analog, FM-recorded video image, and either analog or CD-quality PCM-encoded audio. Later discs used one of the analog channels to record an RF-modulated Dolby Digital/AC3 soundtrack and/or used the PCM tracks to encoded a DTS soundtrack.

LCD: Liquid Crystal Display. A display that consists of two polarizing transparent panels and a liquid crystal surface sandwiched in between. Voltage is applied to certain areas, causing the crystal to turn dark. A light source behind the panel transmits through transparent crystals and is mostly blocked by dark crystals.

LCOS: Liquid Crystal on Silicon

Letterbox: Format used widely on laser disc and many DVDs to fit wide-aspect-ratio movies (1.85:1 and 2.35:1, for example) into a smaller frame, such as the 1.78:1 area of an anamorphic DVD or the 1.33:1 area of a laser disc or video tape. The image is shrunk to fit the screen, leaving blank space on the top and bottom. This process sacrifices some vertical detail that must be used to record the black bars.

LFE: Low Frequency Effects track. The .1 channel of a Dolby Digital, DTS, or SDDS soundtrack. The LFE is strictly low-frequency information (20 to 120 Hz, with 115 dB of dynamic range) that's added to the soundtrack for extra effect. This track does not inherently contain all the bass of the soundtrack.

Line-Level (Low-Level): A level of electrical signals too low to make the average speaker move sufficiently. Amplifiers receive line-level signals and amplify them to speaker level.

LNB: Low-Noise Blocker. The receiving end of a satellite dish.

Low Pass: A filter that lets low frequencies go through but doesn't let high frequencies go through. Same as high cut.

Luminance: The black and white (Y) portion of a composite, Y/C, or Y/Pb/Pr video signal. The luminance channel carries the detail of a video signal. The color channel is laid on top of the luminance signal when creating a picture. Having a separate luminance channel ensures compatibility with black-and-white televisions.

Megachanger: CD or DVD player with massive disc storage capacity, holding 50 or more discs.

MHz: Megahertz, or 1 million Hz.

Midbass: The middle of the bass part of the frequency range, from approximately 50 to 100 Hz (upper bass would be from 100 to 200 Hz). Also used as a term for loudspeaker drivers designed to reproduce both bass and midrange frequencies.

Midrange: The middle of the audio frequency range. Also used as a term for loudspeaker drivers designed to reproduce this range.

MLP: Meridian Lossless Packing. Encoding format that is able to completely reconstruct the original signal at the receiving end. No information is lost or discarded, regardless of how trivial it might be. Used to encode six channels of high-resolution audio on DVD-A.

Mono: Monophonic sound. One channel.

MP3: MPEG-1 Audio Layer-3. Compression scheme used to transfer audio files via the Internet and store in portable players and digital audio servers.

Multiple-Rate Encoding: Instead of locking encoding at a certain constant data rate, it allows the codec to choose whatever rate is best for that portion of the recording. Usually reduces file size with proportionally less loss in quality.

Multisource: System with multiple sources. Can also be used to describe a receiver that can provide multiple different sources into different rooms.

Multiroom: System that provides audio or video to multiple areas. Usually with only one source.

Multizone: System that provides different sources into multiple areas simultaneously.

N-curve: See Academy Curve.

Negative Gain Screen: Material that reflects less light than a reference material. Often used for DLP and LCD projection systems.

Noise: An unwanted portion of a signal such as hiss, hum, whine, static, or buzzing.

NTSC: National Television Standards Committee. Government-directed committee that established the U.S. color TV standard in 1953. Also known, sarcastically, as Never Twice the Same Color or Never The Same Color due to the inherent difficulty in achieving proper color calibration.

Octave: The difference between two frequencies where one is twice the other. For example, 200 Hz is an octave higher than 100 Hz. 400 Hz is one octave higher than 200 hz.

Ohm: A measure of how much something resists (impedes) the flow of electricity. Larger numbers mean more resistance.

Optical Digital Cable: Fiber optic cable that transfers digital audio signals as light pulses.

Passive: Not active. A passive crossover uses no external power and results in insertion loss. A passive speaker is one without internal amplification.

Passive Radiator: A radiating surface (usually similar to a conventional speaker cone) that is not electrically driven but shares the same air space in a sealed cabinet with an electrically driven loudspeaker. This arrangement is functionally similar to a loudspeaker with a vented (ported) cabinet, with the passive radiator serving the duties of the air in the port.

Parametric: Equalizer with adjust-able parameters, such as center frequency and bandwidth (Q), as well as amplitude.

PCM: See Pulse Code Modulation.

Phase: Time relationship between signals; it's all relative.

Piezo: A type of speaker driver that creates sound when a quartz crystal receives electrical energy.

Pixel: Contraction of picture element. The smallest element of data in a video image.

Plasma: Flat-panel display technology that ignites small pockets of gas to light phosphors.

Port: An aperture in a loudspeaker enclosure that helps extend the usable low-frequency output. A ported enclosure is also called vented or bass reflex.

Power Amp: See Amplifier.

Power Output: A measure, usually in watts, of how much energy is modulated by a component.

Preamplifier: A control and switching component that may include equalization functions. The preamp comes in the signal chain before the amplifiers.

Pre Outs: Connectors that provide a line-level output of the internal preamp or surround processor.

Pre Outs/Main Ins: Connectors on a receiver that provide an interruptible signal loop between the output of the internal preamp or surround processor portion of the receiver and the input of the amplifier portion of the receiver.

Pre/Pro: A combination preamp and surround processor.

Processors: Anything that processes an incoming signal in some way. Surround processors, for example, can decode a Dolby Digital signal to send to an amp so you can hear it.

Progressive Scanning: Each frame of a video image is scanned complete, from top to bottom, not interlaced. For example, 480p means that each image frame is made of 480 horizontal lines drawn vertically. Computer images are all progressively scanned. Requires more bandwidth (twice as much vertical information) and a faster horizontal scan frequency than interlaced images of the same resolution.

Projection System: Display that projects image onto a screen.

Pulse Code Modulation: (PCM) a way to convert sound or analog information to binary information (0s and 1s) by taking samples of the sound and record the resulting number as binary information. Used on all CDs, DVD-Audio, and just about every other digital audio format. It can sometimes be found on DVD-Video.

PVR: Personal Video Recorder. Marketing term for Video HDRs.

Q: The magnification or resonance factor of any resonant device or circuit. Also the width of affected frequencies in an equalizer. Shaped somewhat like an adjustable width bell curve.

RCA Jacks: Receptacles for coaxial cables carrying line-level audio signals. Also called phono-type connectors.

Re-EQ: Short for Re-equalization. A feature found on THX-certified receivers and pre/pros. Movie soundtracks are mixed for theaters or far-field monitors with an expected high-frequency roll-off otherwise known as an X-curve. If these soundtracks are not re-mixed for home use, they will sound too bright when played back through home speakers or near-field monitors. Re-EQ inserts an X-curve response into the signal to compensate for this, which takes out some of the soundtrack's excess edginess or brightness.

Rear-Projection Television: Display that projects an image on the backside of a screen material, usually after having been reflected off of a mirror.

Receiver: Any component that receives, or tunes, broadcast signals, be it NTSC, HDTV, DBS, or AM/FM radio. Typically refers to the single component that includes a preamp, surround processor, multichannel amplifier, and AM/FM tuner.

Resonant Frequency: The frequency at which any system vibrates naturally when excited by a stimulus. A tuning fork, for example, resonates at a specific frequency when struck.

Reverberation: The reflections of sound within a closed space.

Reverberation Time: The amount of time it takes the reverberation to decay 60 dB from the level of the original sound.

RF: Radio Frequency. Television signals are modulated onto RF signals and are then demodulated by your television's tuner. VCRs and DBS receivers often include channel 3 or 4 modulators, allowing the output signal to be tuned by the television on those channels. Also, laser discs used an RF signal for modulating Dolby Digital 5.1 soundtracks on some movies. This requires an RF demodulator (usually referred to as an AC3-RF demodulator) before or in the surround processor to decode the signal.

RGB: Red, Green, Blue. Can refer to an unprocessed video signal or the color points of a display device. Together these three colors make up every color seen on a display device.

Ribbon Speaker: A loudspeaker that consists of a thin, corrugated, metallic ribbon suspended in a magnetic field. The ribbon acts electrically like a low-impedance voice coil and mechanically as a diaphragm.

RMS: Root Mean Square or the square root of the arithmetic mean (average) of the square's set of values. A reasonably accurate method of describing an amplifier's power output.

RPTV: Rear-Projection Television

SACD: Super Audio CD. Enhanced audio format with up to six channels of high-resolution audio encoded using DSD. Requires an SACD player. Multichannel also requires a controller with six-channel analog or proprietary digital inputs for full playback.

Sampling Frequency: How often a digital sample is taken of an analog wave. The more samples taken, the more accurate the recording will be. You need to sample at a minimum of twice the highest frequency you want to capture. For example, the 44.1-kilohertz sampling rate of a CD cannot record sounds higher than 22.05 kilohertz.

Scan Lines: The lines drawn by an electron gun in a CRT system to make up the picture. Drawn horizontally, from left to right, starting at the top left and working to the bottom right.

SDTV: Standard Definition Television. Lower resolution subset of the ATSC's DTV system. 480i is typically accepted as an SD signal. Digital broadcasters can offer multiple sub-programs at SDTV quality, as opposed to one or two HD programs. Digital satellite and digital cable often refer to the majority of their programs as SDTV, somewhat erroneously, as neither system has anything to do with DTV, though both, technically, consist of a digital 480i signal.

Sealed: See Acoustic Suspension.

Sensitivity: A measurement (in dB) of the sound-pressure level over a specified frequency range created by a speaker driven by 1 watt (2.83V at 8 ohms) of power with a microphone placed 1 meter away.

Signal-to-Noise Ratio: A comparison of the signal level relative to the noise level. Larger numbers are better.

Soft-Dome Tweeter: A tweeter that uses a soft fabric or plastic dome as the radiating diaphragm.

Soundfield: The total acoustical characteristics of a space, such as ambience; number, timing, and relative level of reflections; ratio of direct to reflected sound; RT-60 time; etc.

Soundstage: The area between two speakers that appears to the listener to be occupied by sonic images. Like a real stage, a soundstage should have width, depth, and height.

Source: A component from which the system's signals originate. DVD player, AM/FM tuners, and VCRs are sources.

Speaker: A component that converts electrical energy into acoustical energy.

Spider: Part of a loudspeaker driver's suspension that helps center the diaphragm and returns it to rest after being moved by an energized voice coil.

SPL: Sound-Pressure Level. Measured in dB.

Subwoofer: A speaker designed to reproduce very low bass frequencies, usually those below about 80 Hz.

Suspension: The elements that hold a loudspeaker driver's moving parts together, allows them to move, and helps return them to rest. Most commonly, these include the flexible surround around the outer rim of the driver and the spider on the underside of the diaphragm. See Spider.

S-VHS: Super VHS. Enhancement to regular VHS that offers improved luminance resolution. (400 lines or so.)

S-Video: See Y/C.

Tactile Transducer: A device that turns electrical energy into mechanical energy, usually used to shake the seating in a theater. Effective in providing visceral impact without increasing the system's actual SPL level.

THD: Total Harmonic Distortion

3:2 Pulldown Recognition or 3:2 Inverse Telecine: Film is usually recorded at 24 frames per second. NTSC video (North America) is 30 frames (60 fields) per second. In order to get smooth motion, the film frames are broken into video fields in a 3-2-3 sequence. 3 fields for the first film frame, 2 fields for the second film frame, and so on. If a line doubler doesn't compensate for the extra field during playback on a progressive-scan display, the image will have noticeable motion artifacts. A line doubler with 3:2 pulldown recognition or 3:2 inverse telecine can see this sequence in the signal and correct for it by making sure the last field in the first frame isn't mixed with the first field of the second frame.

THX: Certification program for home theater equipment. Uses some proprietary features, but mostly assures a base quality level for a given room size. (See THX Select or Ultra.) Is compatible with any and all soundtrack formats. Stands for either Tom Holman's eXperiment, after the engineer who drafted the original standard, or is named after the company's founder George Lucas' first movie, THX 1138. Nobody agrees on which.

THX Select: Certification program for speakers and receivers that assures a base level of quality and performance when played in a room that's between 2,000 and 3,000 cubic feet.

THX Ultra: Certification program for speakers, receivers, and amplifiers that assures a base level of quality and performance when played in a room that's greater than 3,000 cubic feet.

THX Ultra 2: The newest certification from THX, THX Ultra 2 requires amplification for seven channels, boundary compensation for subwoofers, and stricter requirements for amplifiers and speakers than THX Ultra. Dipole speakers are used for the side surround channels. Monopole speakers are used for the surround back channel and are placed next to each other. The Ultra 2 processor accommodates both 5.1 EX/ES soundtracks, as well as multichannel audio recordings by directing ambient sounds to the dipole speakers and discrete effects/sounds to the back channels.

Transducer: Any device that converts one form of energy into another form of energy, specifically when one of the quantities is electrical. Thus, a loudspeaker converts electrical impulses into sound (mechanical impulses), a microphone converts sound into electrical impulses, a solar cell converts light into electricity, etc.

Transmission Line: A (sub)woofer cabinet design where the driver is mounted at one end of a tube with the same diameter as the radiating area of the driver and a length of 1/4 wavelength of the 3dB down frequency. This "tube" may or may not be round and may be folded to decrease the size of the cabinet.

Tuner: See Receiver.

Tweeter: A speaker driver designed to reproduce high frequencies; usually those over approximately 5,000 to 10,000 Hz.

Uniformity: Even distribution across a given space. In video, uniformity can refer to the distribution of light (hot spotting) or color.

Unity Gain: Output that equals the input. Unity gain screen material reflects as much light as the reference material. Has an even dispersion of light.

Universal Remote: Remote that has the commands of numerous brands stored into memory and can control several different devices simultaneously.

VAS: The volume of air that offers the same degree of restoring force on the loudspeaker driver's cone as that of the cone's suspension.

VCR: See Video Cassette Recorder.

VCR Plus: VCR feature that, once programmed, allows the user to input the TV guide code for a given program into the VCR, which then automatically sets itself to record that program.

Vented: See Port or Passive Radiator.

VHS: Vertical Helical Scan (or as JCV calls it, "Video Home System"). Widely used method of recording audio and video electrical signals onto magnetic tape.

Video Cassette Recorder: Device that records audio and video electrical signals onto magnetic tape (aka videotape recorder).

Volt: The unit of electrical potential, or difference in electrical pressure, expressing the difference between two electrical charges.

Watt: A unit of power or energy. One horsepower is equal to 745.7 watts.

Word Length: The sampling rate determines how often an analog wave is sampled; the word length determines the resolution of the sample. The larger the word length, the more accurate the sample as a whole. A 16-bit word length (CD) allows 65,536 different level or volume steps that can be chosen for each sample.

WMA: Windows Media Audio. An audio compression format similar to MP3, but with digital rights management (copy protection and usage restrictions) built-in by Microsoft.

Woofer: A speaker driver designed to reproduce low frequencies.

Wow-and-Flutter: A measurement of speed instability in analog equipment usually applied to cassette transports and turntables. Wow is slow-speed variations, and flutter is fast-speed variations. Lower percentages are better.

X-over: see crossover.

X-curve: An intentional roll-off in a theatrical system's playback response above ~2kHz at 3dB per octave. A modern convention (standardized between 1975 and 1984) specified in ISO Bulletin 2969, it is measured at the rerecording position in a dubbing stage or two-thirds of the way back in a movie theater. Pink noise should measure flat to 2kHz and then should roll-off above that. Home THX processors add this roll-off, when engaged, so that a home video soundtrack will have the same response as it would in a theatrical setting.

Y/C: Abbreviation for luminance/ chrominance, aka S-video signal. Color and detail signals are kept separate, thus preventing composite video artifacts. Cable uses four-pin connector. Used with S-VHS VCRs, DVD players, Hi-8, and DBS receivers.

Y/Pb/Pr: See component video.

Zone: One or more rooms powered by one or more amplifiers, which are all fed by one source. A home can be divided into multiple zones, which can play multiple sources, even though several rooms (say, the kitchen, dining room, and living room) all play the same source.