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Audio Terminology And Definitions Dictionary


D/A Converter (DAC)  The digital-to-analog converter is an electrical circuit that converts a binary coded word (a "sentence" of 0s and 1s) into an equivalent analog voltage (continuous waveform).


Damping     In an acoustical sense, we describe a room that doesn't reflect sound very well as one that's heavily "damped." These rooms usually have curtained walls, sound-absorbent ceilings, carpeted floors, lots of overstuffed furniture, or some combination of these "damping" elements. People also provide damping; an empty theater is more reflective than one that contains a large audience. Speakers may be damped internally with foam, fiberglass, wool, or other absorbent materials.


Damping Factor   A measure of the control an amplifier exerts over a loudspeaker drive unit. Damping factor is a measure of amplifier output impedance relative to  loudspeaker impedance. 


D'Appolito Configuration Named after its designer, Joseph D'Appolito, this is a way of restricting a loudspeaker's dispersion and limiting the area into which it radiates sound. Speakers using the D'Appolito configuration place a tweeter between two midrange drivers. The size of the drivers and their spacing is critical. When properly executed, a D'Appolito configuration results in comparatively little radiation above and below the center axis of the speaker, thus minimizing floor and ceiling reflections.


DAT  Digital Audio Tape. This format introduced in the late Eighties makes use of a rotating drum containing a helical scan head similar to the sort used in video cassette recorders. Unfortunately disagreement between the recording and hi-fi industries led to a refusal by the major record companies to produce pre-recorded DATs or to sanction the release of a non-copyright protected digital tape recorder hardware. By the time a copyright protection system had been agreed, DAT was dead on its feet as a mainstream consumer format. 


Data Reduction Also called "data compression." Any technique that reduces the amount of digital data required to represent a given amount of information. Data reduction enables large amounts of information to be easily and efficiently stored and transmitted. For example, a technology that reduces data by 75 percent (4:1 compression) can store a 16-bit digital word in just four bits. Data reduction technologies used for digital audio must have very carefully designed parameters so as to have a minimal effect on the accuracy of the reproduced sound. (See also: compression.)


DC  Abbreviation for direct current


DCC  Digital Compact Cassette is Philips' backwards compatible digital cassette format. In addition to playing and recording Digital Compact Cassettes, DCC recorders also play standard analogue cassettes. Hence the term backwards compatible. DCC tapes work to 16-bit 44.1kHz sampling. It also features Philips' PASC data reduction system. PASC selectively discards signals thought to be below the threshold of audibility. Soft signals audible in isolation may be masked by louder signals. In such circumstances PASC eliminates the masked signals. 


Decibel (or dB)  The dB is the most common—and most commonly misunderstood—measurement in audio. It doesn't measure anything per se, but rather it measures, on a logarithmic scale, the ratio between two values, whether they be voltage, current, or, most commonly, sound pressure levels (abbreviated dB SPL). An SPL that is 10dB louder than another is considered twice as loud.


Delta/Sigma  A so-called "single-bit" digital signal format where each sample is described in relative terms only. In other words, a sample in a delta-sigma data stream can be only stronger or weaker than the preceding (or following) sample .Delta-sigma signals are inherently less data-intensive than their PCM equivalents. However, they can't be mathematically manipulated as easily, which makes them somewhat more difficult to process. (Sometimes called sigma-delta.)


Diaphragm   The surface of a driver, which pushes against the air to generate sound waves. Examples include a cone or dome (dynamic speaker) or a membrane (planar speaker).


Dielectric  The non conducting space/insulation between two conductors in a cable.


Digital A sampled analogue waveform encoded in the form of on/off pulses. The frequency with which the analog waveform is sampled is its sampling frequency which, in the case of Compact Disc, is set at 44.1kHz (44,100 samples per second). The accuracy of sampling is determined by the word length of each sample. For Compact Disc it is 16-bit. Modern professional digital recorders are capable of almost 32-bit resolution at 384 kHz (as of June 2013).


Digital Coaxial Output     An electrical output connection for a raw digital data stream that uses a single cable with RCA connectors at each end. (See also: digital optical output.)


Digital Filter Any filter used in the digital domain. CD players use oversampling to raise unwanted frequencies away from the audio range. Digital filtering does not produce the phase distortion common to analog filtering.


Digital Optical Output   An optical output connection for the digital data stream. The most common connector today is TOSLink, although the older AT&T "glass" connector is still preferred by some. (See also: digital coaxial output.)


Digital TV An FCC-approved television transmission system wherein the video and audio portions are transmitted digitally and not as analog data. With digital television, the signal is basically "on" or "off." In other words, the intent of DTV technology is that the viewer sees either a good image or nothing at all. There is no gradual signal loss as distance from the transmitter increases. DTV broadcasts can be standard definition, intermediate definition, or high definition. Thus, all HDTV broadcasts are considered DTV, but not all DTV is HDTV.


Diode  The thermionic diode invented in 1904, marks the start of the electronics era. It is the first device for controlling the flow of current in relation to applied voltage, and comprises two electrodes, the heated cathode (electron source) and anode (electron receptor).


Dipolar    A loudspeaker that radiates equal amounts of energy in two opposite directions with opposite polarity. The compressions and rarefactions that constitute sound waves move outward from each side of the enclosure in inverse symmetry (i.e., while one side of the enclosure produces a positive pulse, the opposite side produces a negative pulse). (See also: bipolar.)


Direct Circuit Paths  To employ remote switching wherever possible. In this fashion, we bring the switch to the circuit, rather than lengthening the signal path. Contact points are also kept to a minimum. This helps prevent radio frequency pickup and achieve a lower subjective noise floor.


Direct Current  Current that does not have a positive or negative value. Usually referred to as DC.


Directionality  The tendency in some loudspeakers to beam sound like a laser rather than radiate it equally in all directions. Horn, ribbon and electrostatic speakers tend to be more directional at high frequencies than well designed dome moving coil tweeters, a factor that in extreme situations can impose restrictions on listening and speaker position. 


Direct Radiator A loudspeaker that radiates its energy in one primary direction.  Also called a monopole speaker.


Dispersion    The characteristic angle over which a speaker projects sound. Dispersion is usually measured by attenuation in dB as a measurement microphone is moved from in front of the speaker to off to the side of the speaker. It is usually expressed in dB and degrees relative to the speaker's on-axis response. For example, a typical speaker might have a frequency response that is down 3dB at 5000 Hertz 60 degrees off-axis relative to its on-axis response. Because of the laws of physics and acoustics, speakers tend to have narrowing dispersion with increasing frequency.


Distortion  Any unintended or accidental alteration of an original signal. Distortion can take many forms, the most common being harmonic and intermodulation distortion. Our aural perceptual system tolerates relatively high distortion if the distortion is mathematically related to the original signal, but our ears are intolerant of random distortions that are unrelated to the original signal.


Dither  A low level random noise added to a digital signal to mask highly audible forms of digital distortion.


DivX  Another video compression format, DivX is used primarily for sending video files over the Internet, DivX is based on MPEG4.  It produces very small files by compressing a great deal of video content while maintaining reasonably good image quality. Note:


This is the second time the name DivX has been used. The first so-named system was an attempt to market time-sensitive DVDs that would be unplayable after a set period of time.


DLP    An acronym for Digital Light Processing, a display technology developed by Texas Instruments. DLP uses a chip called a DMD, or Digital Micromirror Device. Today, DLP displays are used primarily for video projectors.


DMM   Direct Metal Mastering. An LP disc mastering process in which silvering and electroplating stages are eliminated.


Dolby Digital     Also known as AC-3, this is Dolby's original technology that utilizes digital processing to deliver 5.1 discrete channels of audio. In its full implementation, Dolby Digital uses five "full-bandwidth" channels (left, right, center, left surround, and right surround) as well as a bass-only low-frequency effects channel for information below 100 Hz. This bass-only channel is the ".1" of the full 5.1 array because it covers approximately one-tenth of the frequency range of a full-bandwidth channel.


Dolby Digital EX     Based on Dolby Digital, the "EX" extension adds a sixth full-range channel, with its speaker located directly behind the listener/viewer.


Dolby Digital + Dolby Digital Plus, or Enhanced AC-3 (E-AC-3), is a surround sound audio codec designed for evolving applications such as streaming media, computer audio, mobile phones, and other internet-based uses. It supports up to eight channels of audio.


Dolby HX Pro  A form of signal processing during recording which prevents self biasing of the signal. HX Pro thus protects loss of high frequency signals through unwanted compression, a useful feature in cassette decks.


Dolby Noise Reduction  Any of a number of double-ended (record encode/playback decode) systems designed to reduce the noise inherent in analog tape recording and mixing. The first example, Dolby A, was designed for professional applications. Dolby B was specifically developed as a consumer format. Dolby C and S formats, both consumer technologies, expand Dolby B's capabilities. Dolby SR is an advanced professional technology.


Dolby ProLogic     A significant step in the transition from stereo to multi-channel sound, this matrix (non-discrete) audio delivery system provides a center channel and enhanced separation, thanks to special "steering" circuitry, for more accurate spatial presentations.


Dolby ProLogic II  A surround sound decoding technology that was developed jointly by Jim Fosgate and Dolby Labs. Dolby ProLogic II can create a "simulated" 5.1 channel surround environment from any two-channel source (such as stereo CDs) as well as from a four-channel Dolby Surround signal. It is not a discrete format, but it makes effective use of matrixing to deliver an adequate 5.1 representation of a stereo film or music soundtrack. (Also called PL II.)


Dolby ProLogic IIx     This adds two rear channels to Dolby Pro Logic II's 5.1 channels, thus making it a 7.1 channel surround decoding system. (Also called PL IIx.)

Dolby ProLogic IIz   An enhancement to earlier ProLogic approaches, Pro Logic IIz offers the option of adding two front height speakers positioned directly above the main left and right speakers. This adds a vertical component to the surround sound field. (Also called PL IIz.)


Dolby 70mm Six-Track  A commercial film sound process that records six individual soundtrack channels (left, center, right, left surround, right surround, subwoofer) on magnetic stripes that have been "painted" onto the 70mm film print. The soundtracks are then read by magnetic tape heads on the projector and reproduced in the theater. Dolby 70mm Six-Track is a discrete analog format using no matrix encoding or decoding. Films made with it can be shown only in specially equipped theaters. Although it offers improved audio performance compared to Dolby Stereo, it is rarely used today because of the expense involved in making prints.


Dolby Stereo Now largely replaced by Dolby Digital, Dolby Stereo is an analog delivery system that allows four individual soundtrack channels (left, center, right, surround) to be recorded onto a 35mm film print using only two optical soundtracks. The four tracks are then recovered when the film is projected. Dolby Stereo uses an analog active matrix encode/decode process and either Dolby A or Dolby SR noise reduction to achieve high-fidelity surround sound in motion picture theaters.


Dolby Stereo Digital     Also called Dolby SR-D or simply Dolby Digital, this is the commercial iteration that allows six individual soundtrack channels (left, center, right, left surround, right surround, and LFE or subwoofer) to be optically printed onto a 35mm film and reproduced in commercial movie theaters. The information is digitally encoded and printed on the film strip in the area between the sprocket holes on the left-hand side of the film. The data is read optically when a film is projected, and is then decoded and reproduced in the theater.


Dolby Surround   Can be used to refer to either:

1.) Dolby Stereo soundtracks that have been transferred to home video formats (e.g., broadcast, VHS tape, laserdisc). With the exception of Dolby A or Dolby SR noise reduction, a Dolby Surround consumer soundtrack is identical to the Dolby Stereo theatrical soundtrack, with the four original tracks remaining encoded onto two stereo tracks. This enables software with Dolby Surround–encoded soundtracks to be played back on home video systems that have mono, stereo, Dolby Surround, or Dolby ProLogic capability. Obviously, this process is not currently promoted, as Dolby Digital has largely taken its place.)

2.) Name given to the passive decoding technology used in early consumer products that can extract only three (LRS) channels of a Dolby Surround soundtrack's four channels of information. Largely replaced in consumer equipment by Dolby Pro Logic decoding, which was, in turn, replaced by PL II, PL IIx, and, most recently, PL IIz.


Dolby Surround Digital  Can refer to: 1.) Dolby Stereo Digital soundtracks that have been transferred to home video formats. The soundtrack is identical to the Dolby Stereo Digital theatrical soundtrack, with the six original tracks encoded onto a digital track on the software.

2.) The digital decoding technology that can extract all six channels of a Dolby Surround Digital soundtrack from a laserdisc or satellite/cable transmission and reproduce them in home video applications.


Dolby TrueHD  A high-definition, digitally based surround sound format. It supports up to eight channels and is bit-for-bit identical to a studio master recording. It is one of the several audio formats used by Blu-ray discs. 


Driver    In a loudspeaker, any element (dynamic woofers and tweeters, electrostatic panels, ribbons, etc.) that moves in direct response to a signal from an amplifier.( See also: midrange driver, tweeter, and woofer.)


Driver  Software that allows for hardware to communicate with another hardware devices.


DSD (Direct Stream Digital)  A single-bit digital data structure used for high-density recording and SA-CD discs. DSD signals are composed of a very high-speed series of individual bits that define amplitude differences rather than absolute values.


DTS  An abbreviation for Digital Theater Systems, DTS refers to a number of surround sound formats that promise enhanced sound quality. The basic technology is known simply as DTS and is a 5.1-channel encoding and decoding system similar to Dolby Digital 5.1. DTS, however, uses less compression in the encoding process. As a result, some feel that DTS provides a better listening experience.


DTS 96/24     While not truly a separate surround sound format, 96/24 is an "upscaled" version of DTS 5.1. Instead of using the standard DTS 48 kHz sampling rate, 96/24 employs a higher 96 kHz sampling rate. Also, 96/24 extends DTS 5.1's 16-bit depth to 24 bits.


DTS Neo:6     A matrix technology, DTS Neo:6 is a surround sound format that mimics Dolby Pro Logic II and IIx. It can extract a 6.1-channel surround field from existing analog two-channel material, such as a stereo CD, movie soundtrack, TV broadcast, etc.


DTS Neo:X    Introduced in 2011, this is an 11.1-channel surround sound format. DTS Neo:X takes cues already present in either 5.1 or 7.1 channel soundtracks and creates height and width channels that route to additional height and width speakers for greater envelopment. 


DTS-ES (Matrix and Discrete)   DTS-ES actually refers to two 6.1-channel surround encoding/decoding systems: DTS-ES Matrix and DTS-ES 6.1 Discrete. DTS-ES Matrix can create a center rear channel from existing DTS 5.1 encoded material, while DTS-ES 6.1 Discrete requires a specially encoded DTS-ES 6.1 Discrete soundtrack.


DTS-HD Master Audio   This format uses lossless compression to create a "core" and "extension" delivery system for systems equipped to decode it. It reverts to lossy compression if the playback system does not include a Master Audio decoder.


Dual Mono Power Amplifier     A dual mono power amplifier is essentially two separate amplifiers in a single chassis. This design achieves better separation between channels, resulting in superior stereo imaging and greater dynamic control. The most expensive examples incorporate separate transformers for each channel. However, many models employ a high-efficiency toroidal transformer with dual windings (one for each channel) and completely isolate the rest of the circuitry for each channel.


Dubbing Stage A specially designed room resembling a combined small movie theater and recording studio control room. Dubbing stages are used by film directors and sound engineers to create film soundtracks. A dubbing stage's audio characteristics are defined by SMPTE standard # 202 and match those of SMPTE-standardized movie theaters so that filmmakers will be able to accurately hear how their films will sound when shown to the public.


DV (Digital Video)   A format is used by many digital camcorders, DV is usually recorded onto Mini DV cassettes. The DV format is memory-intensive even though it employs a form of real-time lossy video compression. A DV clip requires roughly 1 GB of storage for every five minutes of video. (Clips usually are stored on the computer as QuickTime or .avi files.) DV uses "intraframe" compression to encode video at 30 frames/second, thus making it edit-friendly. This is in contrast to the more problematic "interframe" compression, which is based on MPEG1 or MPEG2 codecs and makes editing more difficult because it reduces the number of full frames/second. DV can provide a clean image with up to 520 lines of resolution.


DVD (Digital Versatile Disc)    DVDs can store video, audio, still image, or computer data. 


DVD-Audio    A largely historic high-resolution audio format based on the very large storage capacity of the DVD disc. It offers 5.1 and 7.1 channels (the .1 is for subwoofer) and digital audio specifications of signals including 16/20/24-bit with 44.1/48/96/192kHz sampling rate. This format also includes Dolby AC-3, linear PCM, and MPEG-2. 


DVD Forum   An industry group of over forty manufacturers and technology providers that oversees development and implementation of the technical standards for DVD hardware and software.


DVD-R     The most common, virtually universal recordable DVD format. It is a write-once format, much like the CD-R, that cannot be erased or changed once it is recorded. DVD-R discs have to be finalized at the end of a recording session before they are playable in another DVD player.


DVD+R    A record-once DVD format introduced and backed by Philips and adopted by the other DVD+RW proponents. It promised easier use than DVD-R and was still playable in most current DVD players. DVD+R discs need to be finalized before they can play in another DVD player.


DVD-R DLA double-layer version of a DVD-R. Rarely used today. 


DVD+R DL    Essentially the same as DVD+R except for extended recording capability thanks to its double-layer (DL) structure. The physical differences between DVD+R and DVD+R DL discs may cause some compatibility issues. 


DVD-RW  The DVD equivalent of the rewriteable CD-RW. 


DVD+RW  DVD+RW is a rewritable DVD format backed by Philips, Yamaha, HP, Ricoh, Thomson (RCA), Mitsubishi, APEX, and Sony, among others. DVD+RW claims greater compatibility than DVD-RW with most DVD players. The DVD+RW format is also easier to use in that DVD+RW discs are finalized during recording rather than requiring a separate step at the end of the recording session.


DVD-RAM  More accurately known as DVD—Random Access Memory, DVD-RAM is a rewritable format originally promoted by Panasonic, Toshiba, and other companies. It is not playback-compatible with most standard DVD players or computer-based DVD-ROM drives. It does, however, allow on-disc editing.


DVD Regional Codes    A DVD coding system enforced by the movie industry that is intended to preserve movie distribution rights and agreements.  See the chapter on DVD for more information.


DVI  Short for Digital Visual Interface, an increasingly rare video-only format for connecting a source component to a video display. Now largely supplanted by HDMI


DVR  Short for Digital Video Recorder, a device for recording video programs directly to a hard drive for later playback. DVRs are usually contained in cable and satellite set-top boxes. 


Dynamic Headroom    Usually specified in decibels, dynamic headroom is a measure of an amplifier's ability to generate a significantly higher power level for short periods of time in order to accommodate musical peaks or extreme sound effects. A 3 dB dynamic headroom measurement indicates that the amplifier is able to generate twice the rated power for that brief interval. 


Dynamic Range  The difference, expressed in dB, between the softest and loudest sounds a particular component, system, or medium can process without adding excessive distortion or having the signal "buried" in a residual noise floor. Related to signal-to-noise ratio.


Dynamic Range Compression     Refers to a number of different technologies aimed at changing the relationship between the loudest and quietest parts of a soundtrack so that explosions, for example, are not as loud as they might otherwise be if uncompressed, and soft dialog is more easily heard because it is louder than it would be if the signal were not compressed. Usually reserved for so-called "late-night watching."


Dynamic Speaker   Any loudspeaker that uses dynamic drivers. (See also: moving coil.)













































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