Click on a letter or number to jump to listings of terms that correspond. [ 5 | A | B | C | D | E | F | G | H | I | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y ] Term Definition Demo D-ILA D-ILA = Direct Drive Image Light Amplifier. A development of the original light valve in which the reflectivity of the polarized liquid crystal surface is controlled directly by pixels arrayed on a semiconductor backing. Each pixel can be addressed individually. Hence an alternative description has evolved Liquid Crystal on Silicon, or LCOS. The technology allows for a very high aperture ratio, meaning that the pixels are harder to see. See: ILA, Light Valve, Aperture Ratio, Projector. D-VCR A video cassette recorder (VCR) which can record digital audio and video signals on standard VHS tape. D-VHS See: D-VCR D/A Converter A device that accepts a digital signal as an input and converts it to analog form at its output. D2B Optical This Digital Data Bus (D2B) was developed by Becker in 1995 in collaboration with Philips and C&C Electronics. D2B Optical was the first fiber-optic data transmission system to be used for audio and control data in vehicles with a data rate of approximately 5Mbit/s. DAB DAB (Digital Audio Broadcasting) is a technology standard for broadcasting audio using digital radio transmission. The term digital radio was first used for DAB in 2001. DAC See D/A Converter. Damping Reducing the energy in a vibrating or resonating system by adding electrically, mechanically or acoustically lossy materials or devices. Damping Factor In power amplifiers, it is a measure of the output impedance of the device. Expressed as a number arrived at by dividing the impedance into 8 ohms. For example, an amplifier with an output impedance of 0.04 ohms would have a damping factor of 8/.04=200. This, and higher numbers are common for solid state amps. Tube amplifiers have much higher output impedances and lower damping factors. In practice, the output impedance of the amplifier has almost no effect on loudspeaker damping, but it can have a significant effect on the frequency response of loudspeakers, most of which have frequency-dependent impedances. Within reason, higher numbers are better. DAT Digital Audio Tape. A popular version is R-DAT which employs rotary heads, as is done in VHS video recorders, but on tiny cassettes. Signals are digitally encoded. dB see Decibel. DBO (Dynamic Bass Optimization)A high pass filter with variable cutoff frequency and variable Q, designed to enhance the performance of subwoofers mounted in sealed and vented enclosures. DBO provides bass boost and protection from overexcursion at the lowest frequencies simultaneously. DC Direct Current. A condition in which the polarity of the voltage is constant, and current flows only in one direction. Batteries and rectified AC power supplies are examples of DC power sources. Decade A factor of ten. In frequency, humans can hear a range of about 3 decades: 20-200, 200-2000,2000-20,000 Hz. Decibel A logarithmic measure of relative voltage, current or power. A decibel is one-tenth of a bel, abbreviated dB. In terms of power, 3 dB = 2x, 10 dB = 10x. In terms of current or voltage: 6 dB = 2x. In terms of perceived loudness: 1 dB is just audible, a 10 dB sound level change represents double or half loudness. Demo Demonstration Diaphragm The vibrating portion of a loudspeaker driver that radiates sound. In woofers, diaphragms are commonly conical in shape. Tweeters are often dome shaped. Midrange speakers can be either. Diaphragmatic Absorbers Sound absorbers that remove energy from a sound field by making it do work, moving a surface. Most effective at low frequencies. Vibrations in walls, floors, ceilings, windows, etc are all indications of diaphragmatic absorption at work. Sometimes it is necessary to add custom built units to absorb more energy at specific low frequencies in order to control room resonances. See: Resistive absorbers, Reactive Absorbers. Die Cast Aluminum Baskets Driver baskets that are cast from aluminum. Cast baskets are much stronger than stamped steel and allow for tighter production tolerances and precise driver operation under even the most demanding situations. Diffraction When the direction of a sound wave is changed by obstacles or geometric changes in the sound path. Not to be confused with reflection or refraction. Hearing sound around a corner is an example. In loudspeaker systems, sound is diffracted by the edges of a baffle, in an amount depending on wavelength and the size and shape of the edge. It is a factor in the design. Diffuse Sound Field A sound field in a room that, at any point in the room, has equal energy arriving from all directions. This is an idealized concept that, in practical listening spaces, is never perfectly realized. Diffuser An acoustical device, or surface that, by its shape causes incoming sounds to be reflected outward in many different directions. Diffusion A lack of directional order in a sound field. More reflections from more directions add diffusion. Digital The representation of a quantity in numeric form, normally in binary. In audio, this means that waveforms of sounds are sampled at very high frequencies, and each sample is stored in numeric form, so that the waveform can subsequently be reconstructed. See A/D converter, D/A converter, Analog. Digital Light Processing Developed by Texas Instruments, the heart of this image projection device is a semiconductor chip, operating as a light switch. It contains a rectangular array of hinge-mounted microscopic mirrors; each of these micromirrors measures less than one-fifth the width of a human hair, and corresponds to one pixel in a projected image. Single-chip devices use a color wheel to reproduce color, while three-chip devices dedicate a chip to each of the primary colors, red, green and blue. Digital Multimeter A meter that measures voltage, current, and resistance, and displays the result in numerical form. Digital Satellite System A broadcast system in which digital video and audio signals are delivered to customers' homes by means of signals radiated from a satellite in stationary orbit and received by a small dish antenna. Digital Signal Processor see DSP Digital Television A generic term that describes any of several systems capable of delivering digital video signals. High Definition (HDTV), Intermediate Definition (IDTV), Enhanced-Definition (EDTV) and standard definition (SDTV) are some of the systems. See: HDTV, IDTV, EDTV, SDTV. Digital-to-analog converter See D/A Converter. DIN Stands for: Deutsches Institut für Normung e.V., the German Institute for Standardization. In audio we find such things as DIN connectors, and car audio head units with DIN specified dimensions. Diode An electronic device that blocks current flow in one direction, but allows it in the other. Dipole Classic definition: a loudspeaker that radiates sound from both the front and back faces of the diaphragm. The forward and backward radiated sounds are therefore of opposite polarity (out-of-phase), and they cancel each other when they meet at the +/- 90 degree axes, producing acoustic nulls. The radiation pattern is nominally that of a figure 8. This also applies to microphones, in terms of their directional sensitivity. Contemporary usage: a loudspeaker with bidirectionally aimed drivers that are connected out-of-phase. Since the drivers are not coincident, the null is not perfect, and the off axis frequency response can be very irregular. Direct Sound Sound that arrives at a listener's ear (or a microphone) directly from the sound source, without reflection. Direct Subwoofer Input A connection bypassing the internal crossover of a subwoofer, to allow the connection of A/V receivers and surround processors that already contain their own subwoofer crossovers and adjustments. See: Crossover Directional Interconnects/Wire Since audio is an alternating (AC) signal, overall the electrons in wires will spend exactly half of the time moving in one direction, and half of the time moving in the other. They end up where they started. Since there is no net flow of current, there can be no directional preference in the conducting wires. If there were directional behavior in interconnects or speaker wire, we would have the beginnings of diode behavior, meaning that one half of the audio signal would be distorted - clearly not a good idea. This is part of the 'smoke' of audio. There is, however, one legitimate situation where the orientation of an interconnect matters, and that is if one ground connection has been broken to eliminate a ground loop. In this case the end with the attached ground should be plugged into the signal source. See: Alternating Current, Ground Loop, Unbalanced Connection, Diode. Directivity A measure of the angular dispersion of sound radiating from a loudspeaker. It is known that, for good sound in rooms, loudspeaker system directivity should be relatively constant over most of the frequency range. See: Directivity Index. Directivity Index A numerical representation of the sound dispersion characteristics of a loudspeaker, expressed in dB. It is the difference between the measured on-axis frequency response and the sound power. 0 dB describes an omnidirectional loudspeaker, radiating sound equally in all directions. Increasing numbers describe an increasing bias for sound radiated in the forward direction. See On Axis, Sound Power, Directivity. Discrete In the audio context, discrete refers to sound recordings in which all channels are stored separately. Each channel is completely independent of each other channel. Discrete 5.1 media Discrete 5.1 media include DVD-Audio, DVD-Video and DTS-CDs. The popular 5.1-channel digital formats, like Dolby® Digital and DTS®, have three front channels (left, center and right) and two surround channels, all of which are full bandwidth, and a “.1” channel that is low-frequency only, and used for occasional special effects. Discrete Circuitry The use of separate components such as transistors, resistors, capacitors, and diodes in an electronic circuit instead of IC's (Integrated Circuits) in which these components are fabricated in microscopic size on a silicon chip. Performance and economic factors usually determine which alternative is chosen. Discrete Logic 7® technology See Logic 7 technology. Distortion When an audio signal has been changed by the nonlinear behavior of the microphones, electronics, and loudspeakers. The nonlinearities, whether acoustical, mechanical or electrical, change the audio signals which are passed through them. See: Linear Distortion, Non-Linear Distortion. Diversity Reception An antenna system, occasionally used in cars, employing two or more antennas in a system that constantly seeks out the one(s) with the strongest signal. Advantageous in difficult FM reception areas, like downtown in cities where multipath problems abound. See: Multipath. DLP See: Digital Light Processing DMM see Digital Multimeter. Dolby Pro Logic® An active matrix decoder for Dolby® Surround (Lt, Rt) signals outputting four audio channels (left, center, right and surround). See: Matrix Encode/Decode, Dolby® Surround, Dolby Pro Logic® II. Dolby Pro Logic® II A development of Dolby Pro Logic® in which there is some separation introduced into the two surround audio channels, as well as several other playback options, some of which apply to the playback of stereo music. Dolby® See Dolby® Digital; Dolby® Pro Logic®; Dolby ProLogic® II; Dolby® Stereo; Dolby® Surround; Dolby® B, C and S Dolby® B, C and S Noise reduction systems developed by Dolby Laboratories, and widely used in tape record/play devices. Dolby® Digital An audio signal encoding/decoding system, developed by Dolby Laboratories, that uses perceptual coding to reduce the data rate required to transmit, and the amount of digital space required to store, digital audio signals. Different consumer and professional versions use different amounts of compression, and therefore have different levels of audio quality. It can store mono, stereo and multichannel formats. See Perceptual Coding Dolby® Stereo The name commonly given to Dolby® Surround as it is used in movie theaters. Dolby® Surround A multichannel audio signal that has been matrix encoded for storage in two channels, called Left total and Right total (Lt,Rt). This is not a discrete system, as it incorporates a lot of crosstalk (sounds from one channel leaked into the others). The name also was used in early decoders that did not incorporate active steering to enhance the channel separation. See: Crosstalk, Channel Separation. Dolby® Digital (audio coding 3/AC-3) An audio signal encoding/decoding system, developed by Dolby Laboratories, that uses perceptual coding to reduce the data rate required to transmit, and the amount of digital space required to store, digital audio signals. It can store mono, stereo and multichannel formats. Different consumer and professional versions use different amounts of compression and, therefore, have different levels of audio quality. See Perceptual coding. Dome Loudspeaker A loudspeaker driver having a diaphragm shaped like a dome. Commonly used for tweeters and midrange units. Double-Blind Listening Test A listening test in which the listeners are not aware of the product identities (the first 'blind') and the person conducting the test also is unaware of, or has no control over, which products are being auditioned at any given time (the second 'blind'), and therefore cannot influence the results. Downmix Generally, the process of combining several channels of information into a smaller number of channels. Specifically, a feature of some Dolby Digital playback devices, allowing users to convert the multichannel digital audio into a two-channel Dolby ProLogic compatible signal (Lt, Rt), or a stereo signal, or a mono signal. In all of these downmixes the LFE channel is not included, therefore the downmixed signals are not exactly the same as the original. See: Dolby Digital, LFE, Lt, Rt. downmixing The process of converting a program created in a multichannel format so that it can be played through a system with fewer channels, e.g. 5.1 to stereo. DRC See: Dynamic Range Contol Driver Another name for a raw speaker or transducer, such as a woofer, midrange or tweeter. See: Compression Driver DRM DRM (Digital Radio Mondiale) is a digital radio system for short-, medium- and long-wave. Compared to conventional AM radio, DRM can fit more channels, at higher quality, into a given bandwidth. DSP Digital Signal Processing. Any form of manipulation performed on an audio or video signal while it is in digital form. The term DSP acquired an unfortunate reputation when, in the early days, it came to be associated with artificial reverberation (hall, stadium, etc.) effects that could be added in during playback. Many of these effects were not good. Now, the quality of DSP processing is undisputed, and limited only by the competence of the programmers. DSS See: Digital Satellite System DTCP DTCP (Digital Transmission Content Protection) is a digital encryption method that enables the transport of content-protected audio and video signals via a digital transmission channel from a source (e.g., DVD player) to an end point (e.g., amplifier or display). DTS® An audio signal encoding/decoding system, developed by DTS, Inc., that uses perceptual coding to reduce the data rate required to transmit, and the amount of digital space required to store, digital audio signals. It can store mono, stereo and multichannel formats. Different consumer and professional versions use different amounts of compression and, therefore, have different levels of audio quality. See Perceptual coding. DTS-CDs DTS-CDs are music CDs produced with five discrete channels for playback in multichannel format through suitable decoders. DTV See: Digital Television Dual Cone A speaker that includes a small cone attached to the apex of the woofer cone. At high frequencies, where the woofer cone is unable to respond to the movement of the voice coil fast enough, the small cone vibrates and helps to augment the high frequency response of the speaker. Dual-cone speakers are often used in enrty-level car-audio systems. Dual Voice Coil A speaker that includes two voice coils wound on the same voice coil former. The two voice coils, connected in either series or parallel provide a choice between two total impedance values. Dubbing In film sound, the act of mixing or re-recording components that make up a sound track is called dubbing. Dull In sound quality: the opposite of 'bright', implying a deficiency of high frequency sounds. DVC (Dynamic Volume Control) In car audio systems, this adjusts the volume and frequency response of the playback to compensate for the auditory masking effects of road, aerodynamic and mechanical noises in a moving vehicle. DVD Initially interpreted as meaning Digital Video Disc, but now that there are several uses for the medium, it is more popularly known as the Digital Versatile Disc. DVD, DVD-Video DVD initially stood for Digital Video Disc but, now that there are several uses for the medium, it is more popularly known as the Digital Versatile Disc. DVD-A (DVD-Audio) An audio version of DVD, in which multiple digital audio channels can be stored in uncompressed PCM form, or using a lossless compression algorithm (the digital audio signals are reconstructed without alteration). The massive storage capacity of DVD allows for many options. DVD-Audio An audio version of DVD, in which multiple digital audio channels can be stored in uncompressed PCM form, or using a lossless compression algorithm (the digital audio signals are reconstructed without alteration). The massive storage capacity of DVD allows for many options. DVD-Video DVD with a special directory structure for files that contain uncompressed or compressed audio signals, and still or moving images plus optional subtitles. Usually protected by various digital copy protection measures. DVI Digital Visual Interface. A standard created to convert analog signals into digital signals to interface with both analog and digital monitors. It handles bandwidths in excess of 160 MHz and thus supports UXGA and HDTV. Common in computers and some television and video products. Currently (2003) being combined with HDCP, a copy-protection scheme, for connections between some video sources and displays. See: HDCP, UXGA, HDTV. DVR Digital Video Recorder. A device that records and plays back streaming audio and video signals using a digital hard drive for storage. DX A short form for 'distance', referring to radio reception. Some radios have local/DX settings to optimize performance when close to or far from the transmitters. Dynamic Range The difference between the loudest and softest sounds that can be reproduced by a device or format. Usually expressed in dB. Dynamic Range Control DRC is a feature of some Dolby Digital decoders which enables users to reduce the dynamic range of the sound so that late-night listening need not disturb others in the house, or neighbors. See: Dynamic Range.