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D

D1 - D2 - D3.
Digital video recording and playback formats. The D1 system uses component video while the D2 and D3 systems use composite video. By using fully digitized video in recording and playback, many problems such as generation loss and distortion are minimized or eliminated. The digital formats use mainly a 19mm wide magnetic tape (3/4")
D'Appolito Configuration.
A speaker configuration in which a tweeter is "sandwiched" between two midrange drivers.
DAC (Digital to Analog Converter).
Electronic device that decodes digital data (ones and zeroes) into an analog waveform electrical signal that can be amplified and played by loudspeakers (or that can be used by a video display to form an image in the case of video DACs).
Damping.
An audio system's ability to stop playing a signal after it has ended.
Damping Factor.
The ability of an amplifier to tightly control the movement of a speaker driver and stop its movement as the signal ends.
DAT (Digital Audiotape).
A consumer digital audio recording and playback system developed by Sony, with a signal quality capability surpassing that of the CD.
Database.
Data Grade Projector.
Cathode Ray Tube based video projector capable of horizontal scan rates of 31,500 Hz allowing the projector to display line doubled video and computer VGA graphics (at 640 by 480 resolution).
dB (Decibel).
Logarithmic scale measuring the intensity of sound (the sound pressure level); a 10 decibel (dB) increase represents in a doubling of sound level.
DB-25.
Special form of interconnect wire commonly used to connect computers to printers but used in audio to transmit six channels of audio information over a single cable; 25 pin connection and special wire design able to transmit large amounts of line level data at a time
BDMS.
Database Management System.
DBS (Direct Broadcast Satellite).
Digital format for music and video that beams high-powered signals across North America from satellites orbiting above the equator to 18-inch satellite dishes providing a wide range of programming in a high-quality digital format.
DBX.
A scheme for reducing audio noise in recordings by encoding and decoding. Effect is more pronounced than with Dolby.
DDR
Digital Disk Recorder, records digital video (or other data) on a disk and plays it back.
Decay.
One of the four basic stages of an envelope. Refers to the time the sound takes to settle into its sustain level.
Decorrelation.
Technique used in home THX systems to create a more diffuse, full surround sound environment by splitting up the mono surround channel of matrix surround sound systems (Dolby Pro-Logic) into two channels and feeding them alternate information.
Decode.
To separate a composite video signal into its component parts.
Default.
The ``normal'' or ``startup'' state of a hardware device or software application.
Definition.
The aggregate of fine details available on-screen. The higher the image definition, the greater the number of details that can be discerned. During video recording and subsequent playback, several factors can conspire to cause a loss of definition. Among these are the limited frequency response of magnetic tapes and signal losses associated with electronic circuitry employed in the recording process. These losses occur because fine details appear in the highest frequency region of a video signal and this portion is usually the first casualty of signal degradation. Each additional generation of a videotape results in fewer and fewer fine details as losses are accumulated.
Delay.
As commonly used in surround sound audio terms, the delay is the time difference between when a front speaker plays a sound and a rear or surround speaker plays a corresponding sound.
Delay correction.
When an electronic signal travels through electronic circuitry or even through long coaxial cable runs, delay problems may occur. This is manifested as a displaced image and special electronic circuitry is needed to correct it.
Demodulator.
An electronic circuit which separates the audio and video signals from the RF carrier frequency.
Depth of field.
The range of objects in front of a camera lens which are in focus. Smaller f-stops provide greater depth of field, i.e., more of the scene, near to far, will be in focus.
Diaphragm.
The moving part of a speaker driver that generates sound through its movements which in turn create movement of air around the speaker.
Diffraction.
Break-up or distortion of a sound wave created when the sound wave hits a speaker cabinet, grille cover, or other similar component of the speaker that is creating the sound. Diffuse Sound quality described by being hard to localize and fully filling a listening area; spread out.
Digital.
A method of representing data using binary numbers. An analog signal is converted to digital by the use of an analog-to-digital (A/D) converter chip by taking samples of the signal at a fixed time interval (sampling frequency). Assigning a binary number to these samples, this digital stream is then recorded onto magnetic tape. Upon playback, a digital-to-analog (D/A) converter chip reads the binary data and reconstructs the original analog signal. This process virtually eliminates generation loss as every digital-to-digital copy is theoretically an exact duplicate of the original allowing multi-generational dubs to be made without degradation. In actuality of course, digital systems are not perfect and specialized hardware/software is used to correct all but the most severe data loss. Digital signals are virtually immune to noise, distortion, crosstalk, and other quality problems. In addition, digitally based equipment often offers advantages in cost, features, performance and reliability when compared to analog equipment.
Digital Audio.
Method of encoding analog audio signals into digital bits of information typically using pulse code modulation resulting in high-quality signals that suffer from very little distortion and noise compared to analog signals, are easy to record and edit without degradation, are easy to transmit and record and can be modified or adjusted quickly and without signal degradation.
Digital Field Memory.
A feature of certain laserdisc players allowing the use of "special effects" such as slow motion, single frame step playback, pause with the image on the screen and more in any laserdisc format.
Digital Surround Sound.
Surround sound format in which all five channels (left front, front center, right front, right rear, left rear and an optional sixth sub-woofer channel) are discrete and full-range (the subwoofer channel is not full range), recorded in digital audio, and compressed to fit in a smaller space
Digital Synthesis.
The use of numbers to create sounds. Method most often used in today's synthesizers for generating sounds, as compared to analog method employed previously.
Digital Television.
Digital video broadcast standard adopted by the FCC to replace the analog NTSC format; digital television standard composed of 18 formats including 6 high definition (HDTV) formats and 12 standard definition (SDTV) formats.
DIMM. (Dual Inline Memory Module)
A module containing RAM Chips that slots into a motherboard's DIMM slots. A memory board that is effectively a double SIMM. It uses a 168 pin connector, and its 63 bit wide bus allows single modules to be installed in Pentium systems.
Din Plug.
A five-pin connector used by MIDI equipment.
Dipolar Speaker.
Speaker featuring speaker drivers on two opposite sides of a speaker enclosure and wired to operate out of phase (as one driver moves in the other moves out) creating a null to the sides of the speaker (very little sound emanating to the sides) and a broad, spread-out sound in general.
Direct View Video Display.
Video display in which the light produced by a cathode ray tube is viewed directly without first bouncing off a screen; common type of television and video monitor ranging in size from 12 inches to 40 inches (measured diagonally) having a glass screen and being fairly deep.
Directivity.
Perception of how well the sound from a speaker can be located as coming from that speaker; degree to which sound from a speaker travels in a straight line to the listener and can be perceived as coming from a specific source.
Director
Director is a time-based authoring tool. Information is placed on a timeline - defined in terms of frames - and events may be triggered in a specific frame. This makes assembling a Director presentation rather like scripting a film or scoring a piece of music, which is reflected in some of the terminology used.

Director is really two pieces of software - the Director environment itself, through which you can create multimedia presentations using the Score and other interface components and the Lingo scripting language.

DirecTV.
Direct broadcast satellite content provider sending out signals including the networks, most major cable channels, pay-per-view movies, sports programming and audio channels.
Discrete.
Separate with no interaction between elements.
Dispersion.
Describes the radiation pattern of sound waves from a sound source (the sound source being a speaker in terms of audio/video); definition of the amount of air all around a speaker excited by the sound waves it produces.
Distortion.
In video, distortion usually refers to changes in the luminance or chrominance portions of a signal. It may contort the picture and produce improper contrast, faulty luminance levels, twisted images, erroneous colours and snow. In audio, distortion refers to any undesired changes in the waveform of a signal caused by the introduction of spurious elements. The most common audio distortions are harmonic distortion, intermodulation distortion, crossover distortion, transient distortion and phase distortion.
Distribution Amplifier.
An amplifier used to boost a low-level signal travelling over a long distance.
Dithering.
An image rendering technique to make fewer colours look like more colours by placing certain coloured dots close to each other.
Diversity Receiver.
Wireless microphone receiver that can "listen" to a signal from the mike using two antennas. It picks the antenna giving the best signal, thus yielding more reliable reception (fewer audio dropouts).
DivX.
Form of DVD that adds special encryption technology to play specially encoded Divx DVD discs on a pay-per-view basis.
DLP (Digital Light Processing)
Digital video display technology that uses a vast array of tiny mirrors (around 500,000) that pivot on or off to reflect or not reflect red, green and blue light. DLT or Digital Linear Tape A digital tape in a cassette that stores large amounts of data and can play it quickly. The magnetic stripes go the length of the tape.
Dolby 3-Channel.
A pseudo form of surround sound somewhere between stereo two-speaker operation and a full surround sound set-up with surround sound speakers in the rear; Dolby 3-channel uses the front speakers only - the front left, front center and front right speakers.
Dolby B Noise Reduction.
Reduces high frequency hiss noise by 10 decibels.
Dolby C Noise Reduction.
Reduces high frequency hiss noise by 20 decibels.
Dolby Digital.
Discrete digital surround sound format based on Dolby's AC-3 compression scheme to be found on DVDs, some laserdiscs and digital television.
Dolby HX Pro.
Feature used when recording to a tape that extends high frequency range of cassettes and increases high frequency headroom by adjusting tape bias.
Dolby Pro-Logic.
Analog surround sound format using matrix surround technology to encode four channels of audio information (left, center, right and surround) onto two channels creating a surround sound sonic environment for properly encoded movies and other programming.
Dolby Reference
Level Volume level of an audio system with the volume at the 0 decibel setting resulting in 85 decibel volume with a test tone and 105 decibel peaks.
Domain (Database)
A domain is the set of allowable values for one or more attributes.
DOS (Disk Operating System).
  1. Software that controls the computer and manages communications between the programs and the hardware.
  2. Text Based operating system that sits below Windows 95/98 on a PC.
Dot.
A single spot or dot of phosphor found in a cathode ray tube.
Dot Crawl.
Line of slightly but continuously moving dots found where there is a sharp colour separation in a vertical line (for instance, where a bright blue rectangle meets a bright red rectangle in an image) resulting from poor chrominance/luminance filtering.
Dot Pitch.
The horizontal (left to right) distance between the centers of two adjacent (next to each other) phosphor triads (grouping of one red, one green and one blue phosphor) found in a direct-view video display. Driver Individual moving element of a complete speaker system which is attached to the speaker enclosure and which vibrates, generally in a back and forth piston like motion, to produce sound waves when power is applied from an amplifier.
DRAM. (Dymanic Random Access Memory).
The most common type of RAM chips used on DIMMs and SIMMs.
Driver.
A program used by the operating system to communicate with a piece of hardware.
Drop Frame.
  1. American system of time code generation that adjusts the generated data every minute to compensate for the spread of the NTSC television system running at 29.97 frames per second.
  2. SMPTE time code mode that keeps accurate time of day by skipping 108 frames per hour following a formula.
Drum Machine.
An electronic device, usually controllable via MIDI commands, that contains samples of acoustic drum sounds. Used to create percussion parts and patterns.
DOLBY(TM).
A compression/expansion (companding) noise reduction system developed by Ray Dolby, widely used in consumer, professional and broadcast audio applications. Signal-to-noise ratio* improvement is accomplished by processing a signal before recording and reverse-processing the signal upon playback.
Dropout.
A momentary partial or complete loss of picture and/or sound caused by such things as dust, dirt on the videotape or heads, crumpled videotape or flaws in the oxide layer of magnetic tape. Uncompensated dropout produces white or black streaks in the picture.
DSK (Downstream Keying).
An effect available in some special effects generators and video mixers in which one video signal is keyed on top of another video signal. The lightest portions of the DSK signal replace the source video leaving the dark areas showing the original video image. Optionally, the DSK signal can be inverted so the dark portions are keyed rather than the lightest portions allowing a solid colour to be added to the keyed portions. The DSK input is most commonly a video camera or character generator. The DSK signal must be genlocked to the other signals.
DSP (Digital Signal Processing).
Manipulation or alteration of analog signals (commonly audio or video signals) after conversion to a digital format.
DSS (Digital Satellite System).
Broadcast video and audio format that beams high-quality digital programming down to small 18-inch satellite dishes from geostationary satellites rotating around the equator.
DTS (Digital Theater Systems).
Discrete, digital 5.1 surround sound format used for movies and music; competitor of Dolby Digital featuring similar but incompatible compression and coding technologies to place six channels of sound on a DVD or on both digital audio tracks of a laserdisc. Dual-Side Play A feature found on certain laserdisc players allowing the playback of both sides of a laserdisc without requiring the viewer to physically flip the disc.
Dubbing.
Recording audio or video signals from one source to create a copy recording; making a copy.
D-VCR (Digital Video Cassette Recorder).
Audio/video playback and recording device that uses digital information on a standard VHS size tape to produce high-quality, digital video.
DVD (Digital Versatile Disc).
Compact disc sized, 5-inch diameter optical disc capable of holding digital video and audio information for movies, music, computer games, and more. Technological successor to the CD ROM that can store up to 17Gb of data. Read using a DVD-ROM drive on a pc (which can be also read CR-ROMs). There are recordable and rewriteable versions.

DVD vs. CD
Bits are packed more closely on DVD
Spacing between loops on CD - 1.6 µm and min distance between pits on surface is 0.834 µm
Spacing between loops on DVD - 0.74 µm and min distance between pits on surface is 0.4 µm
7-fold increase in storage capacity

DVD employs 2nd layer of pits & lands on top of the 1st layer - dual-layer
Semi-reflective layer on top of reflective layer - by adjusting focus, DVD drive lasers can read each layer separately Almost doubles capacity of disc - 8.5GB
Lower reflectivity of 2nd layer limits storage capacity - not fully double capacity
DVD can be double sided as opposed to single-sided on CDs - this doubles capacity to up to 17GB

DVE(TM) (Digital Video Effects).
These effects are found in special effects generators which employ digital signal processing to create two or three dimensional wipe effects. DVE generators are getting less expensive and the kind of effects they create getting more popular.
DVI (Digital Video Interface).
Multimedia standard for computer generated text and graphics merged in video production. Dynamation Preprogrammed pseudo random motion of particle systems such as snow, rain, fountains, explosions, or flocks of birds. Dynamic contrast control Camera circuit extending its contrast ratio beyond the normal 30:1, allowing very bright and very dark areas to exist in the same picture.
Dynamics.
The relative loudness or softness of a piece of music.
Dynamic Headroom.
The ability of an amplifier to put out more power than its average power output for a short time in order to faithfully reproduce sudden, loud sounds without distorting or clipping.
Dynamic Range.
Difference between the highest and lowest sound levels a sound system reproduces; also the difference between the overload level (the highest possible output) and the noise floor (point where output is at a minimum - if output goes lower it is obscured by distortions or noise making it unusable).
Dynamic Speaker.
Common type of loudspeaker using traditional speaker drivers consisting of diaphragms, voice coils, stationary magnets, suspensions, spiders, and baskets in which a signal applied to the voice coil moves it and the attached speaker diaphragm in relation to the stationary magnet and basket.
Dynamics.
Term used to describe how well a particular sound system can accurately portray sound from the lowest amplitude (lowest volume) signals to those of very high amplitude or volume.

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