Resource Center: How to Speak A/V
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Entries starting with: damping: The application of mechanical impedance, such as from a rubber or silicone material, to the suspension of a speaker diaphragm to reduce the amplitude of a resonance. D’Appolito array: A symmetrical vertical array of speaker drivers, such as a tweeter midway between two woofers or two midrange drivers; the purpose is to limit vertical dispersion. data rate: The rate at which digital information is transmitted or received; in audio and video, the rate is typically measured in kilobits per second (kbps) or megabits per second (Mbps), but it can also be measured in bytes per second. Despite referring to digital data, “kilo” and “mega” here retain their normal metric meanings of 1,000 and 1,000,000, respectively. dBf: Decibels referred to a standard power level of 1 femtowatt (one quadrillionth of a watt) at a tuner or receiver’s FM-antenna terminals. dBFS: Decibels referred to a 0-dB level of digital full-scale, the maximum numerical signal level encodable by a digital audio system. DB-25: One of the family of computer-style D-sub connectors with 25-pin plugs and jacks; sometimes used for transferring multichannel analog audio. DCDi (Directional Correlation Deinterlacing): A video-processing technique, developed by Faroudja, for converting standard interlaced video signals into progressive-scan format. Specifically designed for programs that were originally shot on video rather than film, DCDi processes motion-video information separately from still-video information to produce smoother lines in moving images; see deinterlacing. decibel (dB): The most commonly used measurement unit in audio, a decibel is a logarithmic unit expressing the ratio of two powers, currents, voltages, or sound-pressure levels (SPLs). An increase of 10 dB represents a tenfold increase in power, and an increase of 20 dB represents a tenfold increase in voltage. Doubling the power in watts delivered to a speaker raises its output SPL by about 3 dB. decorrelation: A THX process that scrambles the relative phase of the signals sent to the surround speakers in a home theater system in order to increase the sense of surround-field envelopment. defeat: To bypass the actions of a signal processor, tone controls, or other circuitry. defect tracking: A measure of how well a DVD or CD player’s laser pickup and tracking circuits handle flaws on a disc. deinterlacing: The process of converting an interlaced video signal (for example, the video on a DVD) to a progressive-scan video signal. delta-sigma: A circuit technique used in analog-to-digital and digital-to-analog converters in which it is the change (delta) in the signal and not the signal itself that is encoded. At very high rates of oversampling the changes are small and can be accurately encoded using only 1-bit PCM. See 1-bit D/A converter. depth of field: The range of object distances in a camera image that are in focus at a given aperture and zoom setting. DHCP (Dynamic Host Configuration Protocol): A computer protocol that enables a networked device to automatically extract its IP address from a server that’s also on the network. diaphragm: The moving surface in an audio transducer such as a speaker or microphone; the device in a camera that creates the aperture (also called the “iris”). digital: A digit is a number, and digital devices use numbers in some way. A digital tuner, for example, may use numbers only on its front-panel display, or it may use digital frequency-synthesis tuning circuits. Digits can also be used to represent analog signals, as in digital audio or video. A CD carries a pattern representing a series of 16-bit binary numbers (16-digit strings of 1s and 0s); a CD player converts these numbers into a continuously changing (analog) voltage that represents the recorded music. digital audio output: A coaxial or fiber-optic output found on some CD and DVD players and digital recorders that is used to send digital audio signals to a component with a digital audio input; see SPDIF. digital audio server: A component containing a hard-disk drive and a CD recorder that can rip CDs to the hard drive, encode audio signals from other sources, and send and receive files to/from computers or other digital audio devices on a home network. digital cable-ready: A video component, typically a digital TV, featuring a slot for a CableCARD that enables decoding of premium channels. Digital 8: A development of the 8mm videocassette system that uses standard 8mm tape but records a DV-type digital signal. Digital 8 camcorders will play both Digital 8 and 8mm analog tapes. Digital Light Processing (DLP): A technology developed by Texas Instruments and used in video front projectors and rear-projection TVs that uses a Digital Micromirror Device to create images. Digital Micromirror Device (DMD): A chip used in DLP video projectors whose surface is covered with more than half a million tiny movable mirrors that create images by selectively reflecting light from a lamp. digital signal processing/processor (DSP): A general term for the mathematical manipulation of signals that are in digital form. DSP can be used for a wide variety of tasks, including ambience enhancement, equalization, filtering, time-alignment, and noise reduction of audio and video signals. A digital signal processor can be either a separate component or a part of one. digital subscriber line: see DSL. digital-to-analog (D/A) converter (or DAC): An electronic circuit that converts a series of binary codes (or digital “words”) into a continuous analog voltage. digital TV (DTV): Broadcasts of digital television signals in the U.S. following the standards issued by the ATSC, which specify the 18 formats to be used. The most common high-definition (HDTV) formats are variants of 1080i (1,080 interlaced scan lines) and 720p (720 progressive scan lines), while the standard-definition (SDTV) formats use 480 progressive scan lines (480p) or 480 interlaced scan lines (480i). Though the SDTV formats can have both widescreen (16:9) and conventional (4:3) aspect ratios, HDTV is widescreen only. digital video recorder (DVR): see hard-disk recorder. digitizing: The process of analog-to-digital conversion, which consists of the separate processes of sampling and quantization. D-ILA (Direct-drive Image Light Amplifier): JVC’s reflective liquid-crystal technology used for high-resolution displays, a variant of LCoS (liquid crystal on silicon). dipole: A type of speaker that radiates sound equally in two directions but with opposite phase or polarity (see bipole); often used today for the surround channels in a home theater system. Alternatively, a type of antenna that receives radio signals primarily from the two directions broadside to it — for example, the T-shape antenna often supplied with receivers. direct-radiating speaker: Basically, any kind of speaker that’s not a dipole or a bipole; until dipole surround speakers, most speakers were direct-radiating. Direct Stream Digital (DSD): A Philips/Sony-developed delta-sigma system for recording high-quality digital audio, used in professional recording equipment and the Super Audio CD system. direct-view TV: Usually refers to a CRT set whose single picture tube is intended for viewing head on, not projecting onto a screen. dispersion: How far off its central axis a speaker’s sound can still be heard clearly, particularly at high frequencies; expressed in degrees or in terms of the frequency-response rolloff (in decibels, or dB) at various angles relative to the on-axis response. dissolve: A video scene-transition technique where the old scene is faded down while the new scene is faded up; see fade. distortion: Broadly speaking, any unwanted alteration of a signal; see harmonic distortion, total harmonic distortion, and noise. dither: A very low-level random noise added before digital quantization that turns quantization distortion into more audibly or visibly benign random noise. Dolby Digital (DD): The Dolby Labs format for digital surround sound providing up to 5.1 channels; used in DVDs, the digital TV system, and some laserdiscs; formerly called AC-3 (for Audio Code 3). Dolby Digital EX: A system of encoding a quasi-6.1-channel signal within the 5.1-channel framework of a standard Dolby Digital data stream. The sixth channel is encoded by matrix techniques on the left and right surround channels of the Dolby Digital signal. The first licensed decoding system was THX Surround EX, but some digital surround receivers and processors use a generic matrix-decoding system for 6.1 playback. Dolby Pro Logic (DPL): An enhancement to Dolby Surround decoding that extracts a center channel and improves channel separation by means of logic-steering circuitry. Most DPL decoders today operate in the digital domain. Dolby Pro Logic II and IIx (DPL II, DPL IIx): DPL II is a digital enhancement of DPL that can manipulate a Dolby Surround-encoded or plain two-channel stereo signal to simulate 5.1-channel playback, with separate modes optimized for Movies and Music. DPL IIx adds 6.1/7.1-channel playback for systems with one or two back surround speakers. Dolby Surround: The consumer name for the Dolby Stereo system used for movie soundtracks. Dolby Surround encoding matrixes four channels — left, center, right, and surround — into two stereo-compatible channels (LT/RT) that can be carried on any two-channel sound medium. Basic Dolby Surround decoding extracts the single surround channel to feed a pair of speakers at the sides or back of the room; such decoders have now largely been superseded by Dolby Pro Logic decoders as well as by Dolby Digital systems. dot pitch: The horizontal spacing between repetitions of the red, green, and blue phosphor pattern in a color CRT. It’s measured in millimeters. download: To transfer data such as music, video, text, or still images from an online source to a local storage medium, whether a computer hard-disk drive or a removable flash-memory device; also, transferring audio or other data from a computer to a portable device. driver: An individual woofer, midrange, or tweeter, or other sound-producing transducer within a speaker. DSL (digital subscriber line): A method of high-speed data transfer over ordinary copper telephone lines (see broadband). D-sub: A family of multipin connectors originally for data applications but now finding use in various audio/video capacities. The “D” refers to the connector’s shape. DTCP (Digital Transmission Content Protection): A copy-protection scheme developed by Intel to prevent programming transmitted via a digital connection like FireWire (a.k.a. IEEE 1394 or i.Link) from being copied without permission of the copyright holder. DTS: A multichannel codec developed by Digital Theater Systems and used to carry a 5.1-channel soundtrack on DVDs, CDs, and laserdiscs. DTS is a rival to the more common Dolby Digital format. DTS Extended Surround (DTS-ES): A development of DTS that adds 6.1-channel capability. There were originally two types of DTS-ES, Matrix and Discrete, but all DTS-ES recordings made now are Discrete. DTS-ES Matrix can be decoded by any decoder that also handles DTS-ES Discrete. DTVLink: An IEEE 1394 (a.k.a. FireWire, i.Link) interface found on a digital TV, HDTV tuner, or digital video recorder that meets certain Consumer Electronics Association specifications for interoperability. dubbing: The process of copying a recording, the result being a “dub.” DV: A videotape format that records video and audio as digital signals, most familiar in the MiniDV form used in camcorders (see MiniDV). DVI (Digital Visual Interface): A high-speed digital interface for visual data (both video and still images), originally used for connecting computers with display devices but then adapted for HDTVs, HDTV monitors, and HDTV tuners as well as DVD players; now being superseded by HDMI connectors, which carry digital audio as well; see HDMI. DV in/out: see IEEE 1394. DVD: A high-capacity optical-disc format that enables vast amounts of audio, video, or computer data to be encoded on a laser-read disc the size of a CD. DVD-Audio: A music-oriented DVD format that can carry up to six channels of audio at up to 24 bits resolution, with or without video or interactive content; typical sampling rates are 48, 96, and 192 kHz. Most also carry Dolby Digital or stereo soundtracks for playback (though not at high resolution) on DVD-Video machines that lack DVD-Audio decoders. DVD changer: A DVD player that holds three or more discs at a time. DVD Forum: An international association of hardware manufacturers, movie studios, and recording companies that defines the specs for the DVD format and licenses the right to produce and sell discs and players. DVD-RAM: A rewritable (erasable) recordable DVD format officially supported by the DVD Forum. DVD-RAM discs are compatible only with DVD players designated to play them. DVD+R: A write-once (nonerasable) recordable DVD format. DVD+RW: A rewritable (erasable) recordable DVD format. DVD+RW discs are said to be playable on most newer DVD players. DVD-R: A write-once (nonerasable) recordable DVD format officially supported by the DVD Forum. DVD-RW: A rewritable (erasable) recordable DVD format officially supported by the DVD Forum. DVD-RW can be recorded in two modes, Video (essentially the same as standard DVD-Video) and VR, which allows for extensive editing. Video mode DVD-RW discs are said to be playable on most newer DVD players, but VR mode recordings are less widely compatible. DVD-Video: A DVD format used almost exclusively for movies and other image-intensive program material; it employs MPEG-2 video encoding and Dolby Digital or DTS multichannel plus PCM stereo audio encoding. Most movie DVDs offer up to 5.1 channels of surround sound, and today most come in widescreen format. D-VHS: A development of the Super VHS system that records video and audio as digital data on a special VHS-size videocassette. D-VHS machines will also play standard analog S-VHS and VHS tapes. Some prerecorded HDTV movies are available in this format. dynamic headroom: The difference, in decibels (dB), between an amplifier’s rated continuous average power (at 1 kHz) and the power it can deliver in short bursts (up to 20 milliseconds) for clean, undistorted musical peaks or extreme sound effects; higher figures are better. dynamic range: The difference, in decibels (dB), between the loudest and quietest parts in a recording or between the overload level and the noise floor of a component or a recording medium; higher figures are better. dynamic speaker: A speaker using the most common type of driver technology, in which a diaphragm, usually shaped like an inverted cone, is moved by a voice coil. dynamics: A subjective term describing the ability of a component to render loud and soft musical passages. Abbreviations |
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