Glossary

We have compiled a list of audio, video and security terms that you might find helpful in your quest for knowledge. From A-Z, this glossary should have all the answers.

Glossary of Terms:    A   B   C   D   E   F   G   H   I   J   K   L   M   N   O   P   Q   R   S   T   U   V   W   X   Y   Z  

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A-B Test: A test between two components. For example, a test between two different loud speakers.

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.

AAD: An acronym found on CD cases to indicate that the music was recorded and mastered on in analog (AA) and then stored digitally (D). (See also ADD) (See also DDD)

AC: Alternating Current. An electrical current that periodically changes in magnitude and direction.

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. (See also 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 or closed box speaker enclosure.

Acoustically Voice Matched: Ensuring that the many different loudspeakers used in a Home Theater system have a sufficiently similar timbre match, such that when a sound is panned between them there is no change in character of the sound.

Acoustics: The area of study which deals with the behavior of sound. Also the effect a given environment has on sound.

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.

ADD: An acronym found on CD cases to indicate that the music was recorded in analog (A) and mastered or remastered digitally (D) and then stored digitally (D). (See also AAD) (See also DDD)

AES/EBU: AES/EBU (Audio Engineering Society/European Broadcasting Union) is the name of a digital audio transfer standard. The AES and EBU developed the specifications for the standard. The AES/EBU digital interface is usually implemented using 3-PIN XLR connector.

Alignment: A class of enclosure parameters that provides optimum performance for a woofer with a given value of Q.

Alpha: In sealed enclosure designs, the ratio of Vas to Vb, where Vb is the volume of the box you will build. See also: Sealed Enclosure

Ambience: The acoustic characteristics of a space with regard to reverberation. A room with a lot of reverb is referred to as being live; whereas a room with little or no reverb is considered to be dead.

Ampere (a): The unit of measurement for electrical current in coulombs per second. There is one ampere in a circuit that has one ohm resistance when one volt is applied to the circuit. (See also Ohms Law)

Amplifier: A device which increases signal level (increases it's amplitude). Amplifiers typically increase voltage, current or both.

Amplifier Classes: Audio power amplifiers are classified primarily by the design of the output stage. Classification is based on the amount of time the output devices operate during each cycle of signal swing. Also defined in terms of output bias current, (the amount of current flowing in the output devices with no signal).

Class A operation is where both devices conduct continuously for the entire cycle of signal swing, or the bias current flows in the output devices at all times. The key ingredient of class A operation is that both devices are always on. There is no condition where one or the other is turned off. Because of this, class A amplifiers are single-ended designs with only one type polarity output devices. Class A is the most inefficient of all power amplifier designs, averaging only around 20%. Because of this, class A amplifiers are large, heavy and run very hot. All this is due to the amplifier constantly operating at full power. The positive effect of all this is that class A designs are inherently the most linear, with the least amount of distortion.

Class B operation is the opposite of class A. Both output devices are never allowed to be on at the same time, or the bias is set so that current flow in a specific output device is zero when not stimulated with an input signal, i.e., the current in a specific output flows for one half cycle. Thus each output device is on for exactly one half of a complete sinusoidal signal cycle. Due to this operation, class B designs show high efficiency but poor linearity around the crossover region. This is due to the time it takes to turn one device off and the other device on, which translates into extreme crossover distortion. Thus restricting class B designs to power consumption critical applications, e.g., battery operated equipment, such as 2-way radio and other communications audio.

Class AB operation allows both devices to be on at the same time (like in class A), but just barely. The output bias is set so that current flows in a specific output device appreciably more than a half cycle but less than the entire cycle. That is, only a small amount of current is allowed to flow through both devices, unlike the complete load current of class A designs, but enough to keep each device operating so they respond instantly to input voltage demands. Thus the inherent non-linearity of class B designs is eliminated, without the gross inefficiencies of the class A design. It is this combination of good efficiency (around 50%) with excellent linearity that makes class AB the most popular audio amplifier design.

Class AB plus B design involves two pairs of output devices: one pair operates class AB while the other (slave) pair operates class B.

Class D operation is switching, hence the term switching power amplifier. Here the output devices are rapidly switched on and off at least twice for each cycle. Since the output devices are either completely on or completely off they do not theoretically dissipate any power. Consequently class D operation is theoretically 100% efficient, but this requires zero on-impedance switches with infinitely fast switching times -- a product we're still waiting for; meanwhile designs do exist with true efficiencies approaching 90%.

Class G operation involves changing the power supply voltage from a lower level to a higher level when larger output swings are required. There have been several ways to do this. The simplest involves a single class AB output stage that is connected to two power supply rails by a diode, or a transistor switch. The design is such that for most musical program material, the output stage is connected to the lower supply voltage, and automatically switches to the higher rails for large signal peaks. Another approach uses two class AB output stages, each connected to a different power supply voltage, with the magnitude of the input signal determining the signal path. Using two power supplies improves efficiency enough to allow significantly more power for a given size and weight. Class G is becoming common for pro audio designs.

Class H operation takes the class G design one step further and actually modulates the higher power supply voltage by the input signal. This allows the power supply to track the audio input and provide just enough voltage for optimum operation of the output devices. The efficiency of class H is comparable to class G designs.

Amplifier, Power: An amplifier without tone controls, usually with a higher power output than a line amplifier or pre-amp. Commonly used to drive loudspeakers.

Amplitude (amp): The level (perceived as audible volume) of an electrical or acoustic signal. Shown as the value of the vertical axis on a typical graph of a sound wave.

Analog: An electrical signal analogous to the original sounds in non-digital form. For example, LPs and cassette tapes store audio in an analog form. Any quantity which varies continuously without distinct steps. For sound waves in air, this refers to the continuous variation in air pressure; for an audio signal, this refers to the continuous variation in current or voltage.

Anamorphic: Process that horizontally condenses (squeezes) a 16:9 image into a 4:3 space, preserving 25 percent more vertical resolution than letter boxing 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 DVD's. Also called Enhanced for Wide screen or Enhanced for 16:9.

Aperiodic: Refers to a type of bass-cabinet loading. An aperiodic enclosure type usually features a very restrictive, (damped), port. The purpose of this restrictive port is not to extend bass response, but lower the Q of the system and reduce the impedance peak at resonance. Most restrictive ports are heavily stuffed with fiberglass, dacron or foam.

Aperture Grille: In a color picture tube, a shadow mask consisting of a metal sheet with thin vertical openings instead of circular holes.

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 wide screen movies (films with aspect ratios wider than 1.33:1) are displayed on 1.33:1 televisions, the image must be letter boxed, 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 reduce the amplitude of an electrical signal usually by using a volume control, fader or pad. Also to reduce sound levels acoustically through the use of acoustic absorbers, resonators or structural materials.

Audio/Video (A/V): Any system or component that involves both audio and video elements, like a receiver or preamplifier that switches video signals and processes multi channel audio signals (including surround sound decoding) for a home theater system.

Audiophile: An individual who draws great enjoyment from listening to music through high-quality audio reproduction systems.

Aux (auxiliary): An input on a receiver, integrated amplifier or preamplifier that can be used to connect line-level source components. Also, any general-purpose A/V input.

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Backlighting: A technique of illuminating the buttons and keys on a remote control so they can be identified in a dark room.

Balance: A control that changes the relative volume level in two or more channels

Balanced: When positive and negative signal wires have a separate earthed (grounded) shield around them to improve interference rejection. Unbalanced connections use a coaxial cable with a single core and the outer shield doubles as the signal return path. are less apt to pick up external noise.

Band-pass Filter: An electric circuit designed to pass only middle frequencies.

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: The total frequency range of any system.

Bass: The low end of the audio frequency spectrum, from approximately 20 Hz up to 400 Hz.

Bass Blocker: First order high-pass crossovers (non-polarized capacitors), generally used on midbass or dash speakers to keep them from reproducing deep bass frequencies.

Bass Drive Unit (Woofer): A drive unit designed to produce bass frequencies only. In classic two-way speakers the bass drive units are more accurately described as bass/midrange units.

Bass-Reflex: A type of loudspeaker enclosure in which the sound emitted from the back of the woofer's diaphragm is used to augment low-frequency output by feeding it through a port of passive radiator.

Beaming: The tendency of a loudspeaker to concentrate the sound in a narrow path instead of spreading it out.

Bessel Crossover: A type of crossover design characterized by having a linear or maximally flat phase response. Linear phase response results in constant time-delay (all frequencies within the passband are delayed the same amount). Consequently the value of linear phase is it reproduces a near-perfect step response with no overshoot or ringing. The downside of the Bessel is a slow roll-off rate. The same circuit complexity in a Butterworth response rolls off much faster.

Bi-Amplification: The use of two amplifiers, one for the lows, one for the highs in a speaker system. Bi-amplification can be built into the speaker design or accomplished with the use of external amplifiers and electronic crossovers.

Bi-polar: 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: The use of two pairs of speaker wire from the same amplifier to separate bass and treble inputs on the speaker.

Bit: Originally short for Binary Digit. In digital, the small unit of information. A bit represents either an on of off value represented by a 0 or 1.

Bit Stream: Refers to a stream of bits transmitted over a communications line between two devices.

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.

BNC: A type of 75 ohm connection often used in video and digital audio. The BNC format utilizes a locking adapter.

Boomy: The smearing of transients that makes bass reproduction sound muddled, usually because of improperly designed sealed (to small), ported (to small or tuned improperly), and bandpass enclosures.

Bridging: combining both left and right stereo channels on an automotive amplifier into one higher powered mono channel. When an amplifier is bridged, the impedance that the amplifier sees is calculated based upon the output of both stereo channels. Here is a simple formula to help define this:

Bridged Mono Impedance = (Y / X)/2

Y = impedance of driver(s) (both drivers should be identical)

X = # of drivers in circuit

Based on this formula, hooking up one 4 ohm sub bridged mono would be equal to hooking up two 2 ohm subs in stereo, one to each channel.

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. For audio, something referred to as bright has too much treble or high-frequency sound. (See also Black Level)

Butterworth Crossover: A type of crossover circuit design having a maximally flat magnitude response, i.e., no amplitude ripple in the passband. This circuit is based upon Butterworth functions, also know as Butterworth polynomials.

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Capacitor: A device made up of two metallic plates separated by a dielectric (insulating material). Used to store electrical energy in the electrostatic field between the plates. It produces an impedance to an AC current.

Casa: A multi-source/multi-room audio control system, that can be controlled from a hand held IR (infra red) remote, or through an in-wall keypad. It is designed to offer a high quality permanent audio installation, reliably and independently serving many rooms in one home through a simple yet powerful user-interface.

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.

CD: Also known as Compact Disc. An optical disc storage media that is designed to store audio, video, and computer data in a digital format. CD's have a capacity to store 700 Mb (megabytes) of data. The digital information in a standard audio CD is encoded in the PCM format. (See also PCM)

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 multi channel 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.

Channel Balance: In a stereo system, the level balance between left and right channels. Properly balanced, the image should be centered between the left-right speakers. In a home-theater system, refers to achieving correct balance between all the channels of the system.

Chassis: Frame or basket that houses the midrange or bass driver components.

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

Circuit Breaker: An electrical switch that automatically breaks a circuit if the current through it is too high, then can be manually reset. Performs the same function as a fuse, without the need for replacement after it is activated.

Classes, Amplifier: Basically, amplifying the audio signal means using the wall-current (usually either 120 or 240 volts) to increase the amplitude of the audio signal from milliwatts(mW) to watts (W). Different classes of amplifiers accomplish this in different ways. Turning a vacuum tube on or off with current demand increases the efficiency of the amplifier but may add switching distortion. A Class A amplifier is relatively inefficient, converting much energy to heat, but has no switching distortion. (See also Amplifier Classes)

Clipping: Audible distortion occurring when the peaks of an amplifier's output are flattened (or clipped). When the input is too high, an amplifier has insufficient power to accurately reproduce the output waveform.

Cms: Mechanical suspension compliance of a driver, consisting of the spider and surround.

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.

Coaxial Driver: A speaker composed of two individual voice coils and cones; used for reproduction of sounds in two segments of the sound spectrum.

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

Coloration: Any shift away from the natural rendition of music. Coloration is undesirable - boomy bass, a nasal midband or a splashy treble, for instance. All colorations tend to get in the way of the music.

Compliance: The relative stiffness of a speaker suspension, specified as Vas.

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.

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 (Audio): Compression is when the amplitude is squashed to reduce the level difference between the loud and soft parts of the music (the peaks and troughs on the wave form). This is often used by radio stations to improve the sound of cheap radios with limited output capability when played loud. It is usually avoided in Hi-Fi, because it restricts dynamics. However, with powered subwoofers, a form of compression called soft clipping can be useful to avoid the harsh sound of transistors clipping when the amplifier is used near its limit. It's similar to the way valves (tubes) limit their output.

Conductor: Materials along which electrons will flow, making them suitable for use as connecting links in electrical circuits.

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

Conventional Current: The representation of current as flowing from positive to negative potential when describing the behaviour of electricity, despite the reality that the actual electrons constituting that flow move from negative to positive potentials.

Crossover: A frequency divider. Crossovers are used in speakers to route the various frequency ranges to the appropriate drivers. Additionally, many crossovers contain various filters to stabilize the impedance load of the speaker and or shape the frequency response. Some crossovers contain levels controls to attenuate various parts of the signal. A passive crossover uses capacitors, coils and resistors, usually at speaker level.

A passive crossover is load dependent (the transition may not be very smooth or accurate if a different speaker is substituted for the one the crossover was designed for). An active crossover is based on integrated circuits (ICs), discreet transistors or tubes. An active crossover is impedance buffered and gives a consistent and accurate transition regardless of load.

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: High and low pass filters used for speakers do not cut-off frequencies like brick walls. The rolloff occurs over a number of octaves. Common filter slopes for speakers are 1st through 4th order corresponding to 6db/oct to 24db/oct. For example, a 1st. order, 6db/oct high pass filter at 100hz will pass 6db less energy at 50Hz and 12db less energy at 25Hz. Within the common 1st through 4th filters there is an endless variety of types including Butterworth, Linkwitz-Riley, Bessel, Chebychev, etc. Salesmen and product literature will sometimes make claims of clear superiority for the filter used in the product they are trying to sell. Since the subject fills books, suffice it to say that there is no one best filter, it depends on application and intended outcome. Good designers use the filters required to get the optimum performance from the system.

Crosstalk: Unwanted breakthrough of one channel into another. Also refers to the distortion that occurs when some signal from a music source that you are not listening to leaks into the circuit of the source that you are listening to.

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

Current: The flow of electrons along a conductor.

Current (I): The flow of electrical charge measured in amperes

Cycles Per Second: The unit of measure denoting frequency. (See also Hertz - Hz) (See also Frequency)

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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.

DAC: A Digital to Audio Converter. Converts a digital bitstream to an analog signal. Can be a separate unit or an internal chip set.

DC: Direct Current. Current that moves in only one direction.

DDD: An acronym found on CD cases to indicate that the music was recorded (D) and mastered (D) and stored (D) digitally. (See also ADD) (See also AAD)

De-coupling: In a loud speaker - the separating of each drive unit from its enclosure, and also each enclosure from the others, such that no vibration is transmitted from one to another.

Decibel (dB): Named after Alexander Graham Bell. 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.

- 0 dB is the threshold of hearing
- 130 dB is the threshold of pain.
- Whisper: 15-25 dB
- Quiet background: about 35 dB
- Normal home or office background: 40-60 dB
- Normal speaking voice: 65-70 dB
- Orchestral climax: 105 dB
- Live Rock music: 120 dB+
- Jet aircraft: 140-180 dB


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 moves and produces the sound. It usually has the shape of a cone or dome.

Dielectric: Insulating materials exposed to electric fields are called dielectrics. Dielectrics are necessary parts in the construction of any cable because they prevent oxidation and keep the conductors from touching one another. In audio cables, relatively low voltage and current levels mean that dielectric strength is not the most important factor. Far more significant in its effect on the sound is a material's dielectric absorption. This characteristic describes the way a dielectric may discharge a secondary signal into the conductor out of phase with the audio signal.

As a current is passed through a conductor, an electromagnetic field is created which interacts with the dielectric material and temporarily displaces the molecular structure. If the dielectric material has good elasticity and can return quickly to its normal state, then the material is said to have low dielectric hysteresis or loss and will have little audible effect on the signal.

Diffraction: The re-radiation of sound waves at discontinuities such as cabinet edges. The time-delayed wave interferes with the original sound output, causing peaks and dips in the frequency response and smearing the transient response.

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: Represented by a numerical code. For sound, the conversion of an analogue waveform to a series of numbers representing the instantaneous amplitude for each sample taken, the storage of those numbers, and the eventual conversion back to analog format for replay.

Digital Dolby: 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 Digital and Pro-Logic are registered trademarks of Dolby Laboratories Inc.) (See also AC3)

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

Dispersion: The spreading of sound waves as they leave a source. The spreading of sound waves as they leave a source.

Dispersion Modifier: Center bullet in a midrange driver in place of a conventional dust cap. It improves dispersion in the mid-frequencies, and helps to maintain the high frequency response of midrange units.

Dither: The method used in digital systems to smooth out the transitions from one bit to another at low levels. Dither makes a digital recording sound and behave more like analog. The better a recording is dithered, the higher its apparent resolution.

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. (See also DMD)

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 also 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 Digital EX Surround: An enhancement to the Dolby Digital 5.1 where a rear center channel has been added creating a 6.1 format. The Dolby Digital Surround EX format does not add an additional discreet recorded channel. The new rear center channel is matrix-encoded in the Dolby Digital left and right surround signals. The recorded Dolby Digital audio consists of five discrete main channels and a sixth, low-frequency-effects (LFE) channel. The two rear surround channels carry the signal for the rear center channel. The Dolby Digital Surround EX format made is debut in the 1999 movie Star Wars Episode I - The Phantom Menace.

Dolby Pro Logic: An earlier form of surround sound. Four separate signals are encoded in a 2-channel recording and re-separated by the processor into left, centre, right and surround channels. The surround channel is usually fed to 2 speakers at the rear. (Dolby and Pro-Logic are registered trademarks of Dolby Laboratories Inc.) (See also Dolby Surround)

Dolby Stereo: Developed by Dolby in the early 70s, Dolby Stereo produces 4 channel sound with three channels of sound in the front (left and right for music and effects and centre for dialogue) and a surround channel for effects and atmospheres.

Dolby Surround: Encodes sound for rear effects channels into the stereo tracks. Needs to be replayed through a decoder to produce surround. (Dolby is a registered trademark of Dolby Laboratories Inc.) (See also Dolby Stereo)

Dome Tweeter: A high frequency speaker with a dome-shaped diaphragm.A high frequency speaker with a dome-shaped diaphragm.

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: Direct Stream Digital. A digital encoding format proposed by Sony and Philips used to record SACD albums. DSD samples an audio signal at a fixed rate (frequency) just as in the PCM method. However, instead of recording the volume or amplitude as an absolute number, as in PCM, the DSD method measures and records how much the volume has changed since the last measurement. If the signal is sampled fast enough, the amount of change since the previous sample would be very small. The proposal for DSD is for a sampling rate that's over 2 MHz (2 million times per second). At this high speed the changes in signal strength can be represented with one bit. DSD also compresses the data resulting in a 2:1 reduction. DSD will be able to provide a frequency response from DC to 100 kHz with a dynamic range of 120 dB.

DSP: Digital Signal Processing. DSP can be used to create equalization, compression, etc. of a digital signal.

DTS: Digital Theater Systems. Multi-channel digital surround system that encodes and decodes audio signals enhancing the fidelity of the signal to produce high quality sound. It is used in some movie theatres and is also available in some home theatre digital processors. (See also 5.1 Surround Sound)

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.

Dual / Double Voice Coil (DVC): A voice coil with two windings, generally used in woofers. Each voice coil can be connected to a stereo channel, or both voice coils can be wired in parallel or series to a single channel.

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-Audio
- DVD-R
- DVD-ROM
- DVD-RW
- DVD-Video
- DVD+RW


DVD Audio (DVD-A): An audio standard for high quality audio recorded on DVD's that exceed the capacity and quality of CD's. An DVD-Audio disk is capable of recording audio with frequencies up to 96Khz (compared to CD's at 20kHz) and with a dynamic range of up to 144dB (compared to CD's 96dB). DVD-Audio supports multi-channel recordings.

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 Headroom: The ability of an audio device to respond to musical peaks. For example, an amplifier may only be capable of a sustained 100 watts, but may be able to achieve peaks of 200 watts for the fraction of a second required for an intense, quick sound. In this example the dynamic headroom would equal 3 db.

Dynamic Range: The range between the loudest and the softest sounds that are in a piece of music, or that can be reproduced by a piece of audio equipment without distortion (a ratio expressed in decibels). In speech, the range rarely exceeds 40 dB; in music, it is greatest in orchestral works, where the range may be as much as 75 dB.

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.

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EBP: Efficiency Bandwidth Product. A guide that helps a designer determine whether a driver is more suitable for a sealed or ported enclosure. EBP of less than 50 indicates the driver should be used in a sealed, 50 - 90 indicates flexible design options, over 90 indicates best for a ported enclosure. EBP = Fs / Qes

EDTV - Enhanced Digital Television: EDTV refers to a complete product/system with the following minimum performance attributes:

• Receiver: Receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats
• Display Scanning Format: Has active vertical scanning lines of 480 progressive (480p) or higher
• Aspect Ratio: None Specified
• Audio: Receives and reproduces, and/or outputs Dolby Digital audio

Enhanced Definition Television (EDTV) Monitor: EDTV Monitor refers to a monitor or display with the following minimum performance attributes:

• Display Scanning Format: Has active vertical scanning lines of 480 progressive (480p) or higher
• Aspect Ratio: None specified

Enhanced Definition Television (EDTV) Tuner: EDTV Tuner refers to a RF receiver with the following minimum performance attributes:

• Receiver: Receives ATSC terrestrial digital transmissions and decodes all ATSC Table 3 video formats
• Outputs: Outputs the ATSC Table 3 720p and 1080i/p and 480p formats with minimum active vertical scanning lines of 480p. Alternatively, the output can be a digital bitstream output capable of transporting 480p, except the ATSC Table 3 480i format can be output at 480i.
• Audio: Receives and reproduces, and/or outputs Dolby Digital audio

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.

Electronic Crossover: Uses active circuitry to send signals to appropriate drivers. More efficient than passive crossovers. This is also known as an active crossover. (See also Crossover)

Electrostatic Speaker: 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.

Equalizer (EQ): Electronic set of filters used to boost or attenuate certain frequencies.

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

Euphonic: Pleasing. As a descriptive audio term, usually refers to a coloration or inaccuracy that non-the-less may be sonically pleasing.

Extension: How extended a range of frequencies the device can reproduce accurately. Bass extension refers to how low of a frequency tone the system will reproduce; high-frequency extension refers to how high in frequency the system will play.

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F3: The roll-off frequency at which the driver's response is down -3dB from the level of it's midband response.

Farad: The basic unit of capacitance. A capacitor has a value of one farad when it can store one coulomb of charge with one volt across it.

Fb: The tuned frequency of a ported box.

Fc or Fcb: The system resonance frequency of a driver in a sealed box. The system resonance frequency of a driver in a sealed box.

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.

Fibrecrete: A mixture of concrete and fibres, unique to B&W for loudspeaker manufacture. This material was used, for example, to line the inside of the midrange enclosure that sits on top of the bass cabinet of the Matrix 801 and 802. Fibrecrete stiffens and deadens the structure, resulting in minimal mechanical resonance.

Filter: An electrical circuit or mechanical device that removes or attenuates energy at certain frequencies. An electrical circuit or mechanical device that removes or attenuates energy at certain frequencies.

FireWire: FireWire is the popular name for a high-speed digital standard for connecting peripherals such as digital video cameras, audio components and computer devices. FireWire was originally developed by Apple Computer as a replacement for the SCSI bus. IEEE 1394 is formal name for the standard. Vendors must obtain a license from Apple to use the term FireWire. (See also IEEE 1394 )

Flat Response: The faithful reproduction of an audio signal. Specifically, the variations in output level of less than 1 dB above or below a median level over the audio spectrum.

Fletcher-Munson Curve: Our sensitivity to sound depends on its frequency and volume. Human ears are most sensitive to sounds in the midrange. At lower volume levels humans are less sensitive to sounds away from the midrange, bass and treble sounds seem reduced in intensity at lower listening levels.

Flowport: A dimpled and flared port tube that reduces the turbulence of the air flow in the pipe, virtually eliminating chuffing noises.

Free Air Response: The natural resonant frequency of a driver when operating outside an enclosure.

Frequency: The measurement of the number of cycles per second in an audio tone or an alternating current. Humans perceive frequency subjectively as pitch (eg: 440Hz = A). The range of human hearing is typically considered to range from 20Hz to 20,000Hz - (20Hz - 20kHz). The number of cycles (vibrations) per second. 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). (See also Hertz-Hz) (See also Cycles Per Second)

Fs: The frequency of resonance for a driver in free air.

Full-Range: A speaker designed to reproduce all or most of the sound spectrum.

Fundamental: The lowest frequency of a note in a complex wave form or chord.

Fuse: A safety device consisting of a low melting-point wire with a low melting point which breaks an electrical circuit by heating up and melting (fusing) if the current through it is too high.

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Gain: The amount by which an amplifier increases the power of a signal, indicated either in dB (e.g. Gain = +12dB), or as a multiplier (e.g. Gain = x4)

Golden Ratio: The ratio of depth, width, and height based on the Greek Golden Rectangle. Often applied to speaker boxes or listening room design. The Ratio: W = 1.0, Depth = 0.618W, Height = 1.618W.

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Harmonics: Also called overtones, these are vibrations at frequencies that are multiples of the fundamental. Harmonics extend without limit beyond the audible range. They are characterized as even-order and odd-order harmonics. A second-order harmonic is two times the frequency of the fundamental; a third order is three times the fundamental; a fourth order is four times the fundamental; and so forth. Each even-order harmonic: second, fourth, sixth, etc.-is one octave or multiples of one octave higher than the fundamental; these even-order overtones are therefore musically related to the fundamental. Odd-order harmonics, on the other hand: third, fifth, seventh, and up-create a series of notes that are not related to any octave overtones and therefore may have an unpleasant sound. Audio systems that emphasize odd-order harmonics tend to have a harsh, hard quality.

Hass Effect: If sounds arrive from several sources, the ears and brain will identify only the nearest. In other words, if our ears receive similar sounds coming from various sources, the brain will latch onto the sound that arrives first. If the time difference is up to 50 milliseconds, the early arrival sound can dominate the later arrival sound, even if the later arrival is as much as 10 dB louder. The discovery of this effect is attributed to Halmut Haas in 1949.

HDCD: High Definition Compatible Digital (HDCD) is a patented encode/decode process for delivering the full richness and detail of the original microphone feed on Compact Discs and DVD-Audio HDCD-encoded CDs sound better because they are encoded with 20 bits of real musical information, as compared with 16 bits for all other CDs. HDCD overcomes the limitation of the 16-bit CD format by using a sophisticated system to encode the additional 4 bits onto the CD while remaining completely compatible with the existing CD format. HDCD provides more dynamic range, a more focused 3-D soundstage, and extremely natural vocal and musical timbre.

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 copywritten material.

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

Hertz - Hz: The unit of measure denoting frequency. (See also Cycles Per Second) (See also Frequency)

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-pass Filter: A filter with a transmission band starting at a lower cutoff frequency and extending to (theoretically) infinite frequency. In other words, a circuit that discriminates between high and low frequencies and allows only the high frequencies to pass.

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.

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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 and iLink (See also Firewire)

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. (See also Ohm)

Integrated Amplifier: A combination preamp and amplifier in one component.

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).

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.

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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. (See also Hertz - Hz)

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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. This new microdisplay technology (developed by Intel) consists of a liquid crystal layer on top of a pixelated, highly reflective substrate. Below the substrate is a backplane that includes the electronics to drive the pixels. The backplane and liquid crystal are combined into a panel and packaged for use in a projection subsystem or light engine. The LCOS light engine is a projection subsystem built around LCOS panels which enables an RPTV or front projector. An LCOS light engine is assembled from a number of high-quality optical components: lamp, lenses, filters and precision glass, in addition to one, two or three LCOS panels.

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.

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MHz: Megahertz, or 1 million Hz. (See also Hertz - 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 of an audio signal.

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 Range 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.

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

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

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

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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.

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

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

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

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.

PCM: Pulse Code modulation. Aa 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.

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: In digital imaging, a pixel is the smallest piece of information in an image. Pixels are normally arranged in a regular 2-dimensional grid, and are often represented using dots or squares. Each pixel is a sample of an original image, where more samples typically provide a more accurate representation of the original. The intensity of each pixel is variable; in color systems, each pixel has typically three or four components such as red, green, and blue cyan, magenta, yellow, and black.

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

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

Pre Outs/Main In: 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.

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

Processor: Anything that processes an incoming signal in some way. Surround processors, for example, can decode a Dolby Digital signal to send to an amplifier so it can be heard.

Projection System: A video display system that uses a light projector to project images on a screen.

PVR: Personal Video Recorder. A marketing term for Video Hard Disc Recorders.

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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.

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RCA connectors: 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. (See also 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. Display that projects an image on the backside of a screen material, usually after having been reflected off of a mirror.

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

S-Video: A video signal that transmits chrominance and luminance information separately to minimize loss of picture quality. (See also Y/C)

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.

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. (See also Decibel (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 also Spider)

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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. A measure of the distortion content of a signal as represented by equivalent harmonics of that signal and specified as a percentage of the signal amplitude. While the equivalent harmonics represented do not actually exist in the signal, their summation would reproduce the distortion component of the signal. Further, filter separation of the signal into its fundamental and harmonic frequencies yields the harmonics for identification and measurement comparison with the fundamental.

THX: Certification program for home theater equipment. Uses some proprietary features, but mostly assures a base quality level for a given room size (See also THX Select) (See also THX Ultra). THX is compatible with any and all soundtrack formats. The acronym 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.

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. (See also THX Ultra) (See also THX)

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. (See also THX Select) (See also THX)

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. (See also THX Select) (See also THX)

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 subwoofer 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

Tuner: 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. (See also Receiver)

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

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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. Refers to when there is an even dispersion of light.

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

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

VCR Plus: A 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.

VHS: Vertical Helical Scan. Widely used method of recording audio and video electrical signals onto magnetic tape.

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

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Watt (W): A unit of power or energy. Equal to one joule per second.

Woofer: A speaker driver designed to reproduce low frequencies.

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.

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.

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.

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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.

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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. (See also S-Video)

Y/Pb/Pr: Basically, one can think of Y/Pb/Pr as RWB (W for white) when comparing with RGB. In reality all three subsignals are different (contain different proportions of red, green, and blue; the R of RGB is 1.0R + 0.0G + 0.0B). The white (Y, luminance) carries full horizontal resolution while the Pb and Pr carry half. Whereas for RGB all three lines must carry full resolution. Y/Pb/Pr was invented for use in place of RGB to save on total bandwidth requirements. (See also Component Video)

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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.

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