A    Goto Top

A/D   

Analog to digital conversion (or converter). Used at transmission end of broadcast.

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    Goto Top

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.

Addressable Resolution

The highest resolution signal that a display device (TV or monitor) can accept. Caution: Consumers should be aware however, that although a particular device (Digital-HDTV) is able to receive the resolution, it may not be capable of displaying it.

Amplifier    Goto Top

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.

Analog TV  

Analog TV is the NTSC Standard for traditional television broadcasts. Analog signals vary continuously, representing fluctuations in color and brightness.

ANSI Lumens    Goto Top

Industry standard measurement of a projector's brightness. Depending on lamp, optics, and projector design, ANSI lumens range from 200 to 10,000 per projector.

Artifacts   

Unwanted visible effects in the picture created by disturbances in the transmission or image processing, such as 'edge crawl' or 'hanging dots' in analog pictures, or 'pixelation' in digital pictures.

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    Goto Top

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.

B    Goto Top

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. A range of frequencies used to transmit information such as picture and sound. For TV broadcasters, the FCC has allocated 6Mhz for each channel. For DTV, the maximum bit rate possible within the bandwidth is 19.4 Mbps, which is one HDTV channel. SDTV has a lower bit rate, therefore the bandwidth can accommodate more than one channel.  

Bass    Goto Top

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.

Bit Rate

Measured as "bits per second," and used to express the rate at which data is transmitted or processed. The higher the bit rate, the more data that is processed and, typically, the higher the picture resolution.

Bi-Wiring    Goto Top

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.

C    Goto Top
 

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    Goto Top

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    Goto Top

 6 Mhz (bandwidth) section of broadcasting spectrum allocated for one analog NTSC transmission. 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    Goto Top

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.

Compression

A method of electronically reducing the number of bits required to store or transmit data within a specified time or space. The video industry uses several types of compression methods but the method adopted for DTV is called "MPEG2." Four full-range channels of programming and data can be compressed into the same space required by a single analog channel.

Contrast Ratio    Goto Top

The contrast between the brightest white and the darkest black. Higher contrast ratios offer brighter colors and better details. Preferably, you'll want to choose a contrast ratio of at least 100:1.

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    Goto Top

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.

D    Goto Top
 

D/A

Conversion of digital to analog signals. The device is also referred to as DAC (D/A converter). In order for conventional television technology to display digitally transmitted TV data, the data must be decoded first and then converted back to an analog signal.

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    Goto Top

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    Goto Top

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    Goto Top

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    Goto Top

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    Goto Top

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 SurroundÐencoded 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."

Downconvert    Goto Top

A term used to describe the format conversion from a higher resolution input signal number to a lower display number, such as 1080i input to 480i display.

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    Goto Top

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    Goto Top

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    Goto Top

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 CD-R in that it is a write-once medium. Backed by Pioneer, 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

E    Goto Top
 

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    Goto Top

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

Enhanced for 16:9

See Anamorphic.

Enhanced for Widescreen

See Anamorphic.

EPG

Electronic program guide. An on-screen display of channels and program data.

EQ

See Equalization or Equalizer.

Equalization    Goto Top

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.

F    Goto Top
 

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.

F-number    Goto Top

Refers to the amount of brightness that a lens allows through to the screen. Ideally, the f-number should not deviate much from different zoom angles.

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.

G    Goto Top
 

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.

H    Goto Top
 

Hanging Dots

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

HDCP

High Definition Copy Protection. Used with DVI connections and D-Theater D-VHS recordings. Prevents unauthorized copying.

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    Goto Top

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.

I    Goto Top
 

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, É

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    Goto Top

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.

Image Size

The size of a projected image, usually measured diagonally. Make sure to test out the maximum image size for yourself, since manufacturer spec sheets can be rather subjective.

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.

K    Goto Top
 

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.

L    Goto Top
 

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

Lens Shift    Goto Top

The Lens Shift feature of a projector allows the optical lens to be physically shifted up and down (Vertical) or left and right (Horizontal). Most all lens shift mechanisms are motorized with vertical lens shift being the most popular. With a projector that has lens shift you can optically correct for keystone distorted images. It is also used to help geometrically align images when stacking projectors.

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.

Line Doubling    Goto Top

A method, through special circuitry, to modify an NTSC interlaced picture to create an effect similar to a progressively scanned picture. The first field of 262.5 odd-numbered lines is stored in digital memory and combined with the even-numbered lines. Then all 525 lines are scanned in 1/30th of a second. The result is improved detail enhancement from an NTSC source.

LNB

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

Long Throw Lens

A lens designed for projection from the back of a room, or rather the back of a long room. Long throw lenses would be used a projection booth in the back of a theater, etc. A typical long throw lens might have to be 50 to 100 FT back to project a 10FT diagonal image

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.

M    Goto Top
 

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    Goto Top

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    Goto Top

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    Goto Top
 

Native Resolution

If a projector’s native resolution is 800 x 600, that means that the actual number of physical pixels on the display device is 800 x 600.

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.

O    Goto Top
 

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.

P    Goto Top
 

PAL

"Phase Alternation Line" - A signal format used in video equipment in Europe and parts of Asia. PAL signals give you 25 frames per second, and so are incompatible with NTSC, the American video signal format.

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    Goto Top

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.

Polysilicon LCD

Projection technology which utilizes a three-layer LCD panel design. Three separate primary color panels that are used to produce the desired color.

Port    Goto Top

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    Goto Top  

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    Goto Top

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    Goto Top
 

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.

R    Goto Top

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    Goto Top

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.

Resolution

The number of screen pixels that can be displayed by the projector. Most units have a standard of 640x480 pixels or 800x600 pixels (VGA and SVGA, respectively). Higher resolution models are useful if you need to project more of a screen, such as a full layout of a document or drawing. Examples of higher resolutions are XGA (1024x768) and SXGA (1280x1024).

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    Goto Top

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

S    Goto Top
 

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    Goto Top

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.

SECAM

SECAM (Système Electronique Couleur Avec Mémoire) is a signal format used in video equipment in France and the former Soviet Union. It is incompatible with PAL and NTSC formats.

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.

Set-top Box (STB)(also: Decoder, Receiver, and Tuner)

A unit similar to today's cable boxes, which is capable of receiving and decoding DTV broadcasts. A DTV 'Certified' STB can receive all (18) ATSC DTV formats, (including HDTV) and provide a displayable picture.

Short Throw Lens    Goto Top

A lens designed to project the largest possible image from short distance. Most front room projectors use short throw lens. They are often required for rear projection, where the depth behind the screen is limited. A typical short throw lens might produce a diagonal image size of 10 FT, from a distance of 7 to 10 FT.
 

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    Goto Top

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.

Spectrum

A range of frequencies available for over-the-air transmission.

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    Goto Top

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.

SVGA

800 x 600 – This is a popular resolution today, because most notebook computers are SVGA. Matching the plasma or projector resolution with the computer resolution will produce the best results.

S-VHS

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

S-Video

Separated video. An encoded video signal which separates the brightness from color data. S-video can greatly improve the picture when connecting TVs to any high quality video source such as digital broadcast satellite (DBS) and DVDs. Also See Y/C.

SXGA

1,280 x 1,024 – SXGA products are high resolution, and notably more expensive than XGA. These products are targeted for high end personal computer users and low end workstation users. They are used primarily for command and control, engineering and CAD/CAM applications where acute resolution of small details is important.

T    Goto Top

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.

TFT (Thin Film Transistor) LCD

Projection technology which uses only one transparent panel of LCD cells.

THD

Total Harmonic Distortion

Throw Distance

Also known as projection distance. The distance from projector to screen.

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    Goto Top

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    Goto Top

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.

U    Goto Top
 

UHF

Ultra high frequency, the range used by TV channels 14 through 69.

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.

Upconvert

The term used to describe the conversion of a lower apparent resolution to a higher number, such as "upconverting" 720p to 1080i. This is a misnomer, though, since to accomplish this, the horizontal scanning frequency is actually lowered from 45kHz to 33.75kHz. Resolution quality is not improved by this method.

UXGA

1,600 x 1,200 – UXGA is for very high resolution workstation applications that are detail or information intensive. These are expensive plasma tvs that support a broad range of computer equipment. Relatively few products on the market have this native resolution.

V    Goto Top
 

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.

VGA

640 x 480 – This is the lowest data resolution currently on the market, and usually the least expensive

VHF    Goto Top

Very high frequency, the range used by TV channels 2 through 13.

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).

Video Standards

The type of video inputs an LCD projector can accept. Leading standards include NTSC, SECAM, and PAL, with NTSC being the North American video standard.

Volt

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

W    Goto Top
 

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    Goto Top

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.

WSXGA

WSXGA defines a class of SXGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A WSXGA display has 1920 to 1600 horizontal pixels and 1080 to 900 vertical pixels respectively that are used to compose the image delivered by the projector

WXGA

WXGA defines a class of XGA displays with a width resolution sufficient to create an aspect ratio of 16:9. Resolution is defined by the number of individual dots that a display uses to create an image. These dots are called pixels. A WXGA display has 1366 to 1280 horizontal pixels and 768 to 720 vertical pixels respectively that are used to compose the image delivered by the projector.

X    Goto Top
 

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.

XGA

1,024 x 768 - XGA Plasma tvs and projectors are generally more expensive, and are the second most popular resolution format. Many of the newest products are coming out in XGA. They are getting more popular as prices drop and the use of XGA notebook computers increases.

Y    Goto Top

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.

Y, U, V

Also sometimes referred to as Y, Cr, Cb, where a video signal is separated into components of brightness and color, arguably to a degree more advanced than S-video.

Z    Goto Top
 

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.

Zoom Lens

A lens with a variable focal length providing the ability to adjust the size of the image on a screen by adjusting the zoom lens, instead of having to move the projector closer or further

Zoom Lens Ratio

Is the ratio between the smallest and largest image a lens can projector from a fixed distance. For example, a 1.4:1 zoom lens ratio means that a 10 foot image without zoom would be a 14 foot image with full zoom. Conversely, a 10 foot diagonal image at 15 feet with no zoom would still be a 10 image at 21 feet at maximum zoom (15 x 1.4 = 21 feet). A zoom lens is "not as bright" as a fixed lens, and the higher the ratio, the less light output

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.