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- D-CHARACTERS
- A character set used in ISO 9660 Level 1 filenames, if the standard is strictly adhered to (which is not always necessary). Consists of capital A to Z, digits 0 to 9, and the underscore symbol ( _ ).
- D/A CONVERTER (Digital-to-Analog Converter)
- A device that coverts digital data into an analog waveform.
- D1/D2/D3/D5/D6
- Professional digital video recording and playback formats. The use of fully digitized video minimizes or eliminates many problems such as generation loss and distortion.
- D1 is a component video digital recording format that uses data conforming to the ITU-R BT.601-2 (CCIR-601) standard and records on 19mm (3/4”) magnetic tape. (Often used incorrectly to indicate component digital video.)
- D2 is a composite video digital recording format that uses data conforming to SMPTE 244M and records on 19mm (3/4”) magnetic tape. (Often used incorrectly to indicate composite digital video.)
- D3 is a composite video digital recording format that uses data conforming to SMPTE 244M and records on 1/2” magnetic tape.
- D5 is a component video digital recording format that uses data conforming to the ITU-R BT.601-2 (CCIR 601) standard and records on 1/2” magnetic tape.
- D6 is a digital HDTV recording format using D1 tape.
- DAO (Disc-At-Once)
- Mode of writing an entire disc without turning off the recording laser. All of the information to be recorded needs to be staged on the computer’s hard disk prior to recording. The mode is especially useful for creating a master disc for subsequent mass replication thus eliminating the linking and run-in/run-out blocks associated with multisession and packet recording modes, which are often interpreted as uncorrectable errors during the mastering process. It requires the pre-mastering software to send a 'cue sheet' to the CD-R drive that describes the disc layout.
- DAT (Digital Audio Tape)
- A consumer digital audio record/playback system developed by Sony, with a signal quality capability surpassing that of the CD. The DAT format was introduced in the mid 1980s as the first widely distributed consumer digital recording product. It accommodates the high bit rate transfer necessary for digital audio recording by using a rotating head similar to those used in current VCRs. Though the actual tape speed is rather slow, the rotating head gives the system a high relative tape to head speed ratio.
Its introduction in the U.S. was initially met with resistance from record companies and music publishers who claimed that rampant copying would impact their sales. Because of this resistance, its U.S. introduction was delayed, subsequently hampering its acceptance as a viable consumer format. It has since been adopted as a useful format by professionals.
An interesting note is that these same organizations opposed the introduction of the standard audio cassette in the early 1970s for similar reasons. Since the mid 1980s, pre-recorded audio cassette sales have outpaced all other forms of music distribution media combined.
- DATA AREA
- In ISO 9660, the space on a CD-ROM where the user data is written. It begins at the physical sector address 00:02:16.
- DATA COMPRESSION
- (See COMPRESSION)
- DAW (Digital Audio Workstation)
- A computer system containing dedicated hardware and software for editing, processing and mixing digital audio.
- dB (deciBel)
- (See DECIBEL)
- dBk (deciBel - kilowatt)
- A measure of power relative to 1 kilowatt. 0 dBk equals 1 kW.
- dBm (deciBel - milliwatt)
- A measure of power relative to 1 mW. 0 dBm equals 1 mW.
- dBmv
- A measure of voltage gain relative to 1 millivolt at 75 ohms.
- dBr
- This notation expresses the relationship between two program signal levels. It denotes the difference in dB between a measured program signal magnitude and a defined reference magnitude called zero relative level.
- dBu
- 1. A United Kingdom term that shows comparison between a measured value of voltage and a reference value of 0.775 Volt, expressed under conditions in which the impedance at the point of measurement (and of the reference source) are not considered.
2. dB relative to 1 microvolt.
- dBV (deciBel - volt)
- A measure of voltage gain relative to 1 volt.
- dBW (deciBel - watt)
- A measure of power relative to 1 watt. 0 dBm equals 1 watt.
- DCC (Digital Compact Cassette)
- A consumer digital audio record/playback system developed by Philips. The DCC audio format was introduced by Philips in the early 1990s as an alternative to the DAT recording format. It boasts backward compatibility with the original analog audio cassette it was designed to replace through the use of a shell roughly the same size and shape as the standard cassette.
- DD (Dolby Digital)
- (See DOLBY DIGITAL)
- DECIBEL
- A relative and dimensionless unit to measure the ratio of two quantities. In audio, the decibel is used as a measure of voltage, current, or power gain equal to 1/10 of a bel and technically represented by the equations; 20 log (Vout/Vin), 20 log (Iout/In) or 10 log (Pout/Pin) respectively. Put another way, it is a unit for expressing the ratio of two amounts of electric or acoustic signal power. This is equal to 20 times the common logarithm of the voltage or current ratio.
- DECAY TIME
- The length of time it takes an audio limiter or compressor to release it's action on an audio signal. (See ATTACK TIME)
- DECODE
- To expand a compressed audio signal or separate a composite video signal into its component parts.
- DEFINITION
- The aggregate of fine details available on a video 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 CORRECTION
- When a video 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.
- DIGITAL
- An adjective used to describe a method of representing data using binary numbers. An analog signal is converted to digital using an analog-to-digital (A/D) converter chip by taking samples of the signal at a fixed time interval (sampling frequency). Assigning a discrete binary number to each of these samples, the digital stream is then recorded onto some data storage media (typically magnetic tape, optical disk or hard drive.) Upon playback, a digital-to-analog (D/A) converter chip reads the binary data stream and reconstructs the original analog signal.
Unlike analog storage methods, data stored or transferred in digital form is immune to noise, distortion, crosstalk and signal degradation over time and virtually eliminates generation loss, as every digital-to-digital copy is theoretically an exact duplicate of the original. In this way, multi-generational dubs can be made without degradation. In actuality of course, digital systems are not perfect and specialized hardware/software error correction schemes are used to correct all but the most severe data losses.
Examples of digitally stored information are the compact disc, laserdisc and the data on a computer hard drive. In addition, digitally based equipment often offers advantages in cost, features, performance and reliability when compared to analog equipment. (See ANALOG)
- DIGITAL DELAY
- A term used to describe a "black box" which delays an audio signal in millisecond increments for use in recording studios or public address systems. The signal is converted internally to a digital signal and passed through various components "bucket brigade style" to delay the processed signal compared to the original signal.
- DIN (Deutsche Industrie Norme)
- An international connector standard. DIN connectors carry both audio and video signals and are common on equipment in Europe.
- DISSOLVE
- A process whereby one video signal is gradually faded out while a second image simultaneously replaces the original one.
- 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 colors 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
- A device which splits (distributes) one audio and/or video source to several audio/video devices.
- In audio, distribution amplifiers are typically used to make single source signals available to multiple devices without compromising the integrity of the original signal, by compensating for long cable runs, properly terminating all circuits and keeping interaction between all devices to a minimum.
- In video, distribution amplifiers are used in duplication studios where many tape copies must be generated from one source or in multiple display setups where many monitors must carry the same picture, etc.
- DITHER
- Random data or noise that linearizes digital audio. Adding dither can actually increase the apparent resolution of audio signals which are operating in the lowest ranges (least-significant bits) of both A/D and D/A converters and also reduce requantizing distortion. Virtually all modern A/D converters add dither to the analog signals they process; therefore, when you add dither to a digital signal, you are actually redithering or dithering again.
- DOLBY®
- 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.
- DOLBY DIGITAL
- A multi-channel audio format that allows 1 to 7.1 channels of sound for playback on equipment with a Dolby Digital-compatible decoder. This lossy audio compression format is common in movie theaters, standard on DVD-Video discs and will be used in future HDTV broadcasts. Fortunately, even in the absence of a proper decoder, all DVD-Video players will “downmix” the signal into two-channel surround. (See also DTS)
- DOW (Direct OverWrite)
- Method of writing new data over existing data in a single-pass. CD-RW is an example of a Direct Overwrite system.
- 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.
- DSD (Direct Stream Digital)
- Digital audio recording format used for the new SACD (Super Audio CD) developed by Sony. Unlike the PCM recording format used for the standard CD, DSD uses 1-bit sampling at 2.88MHz and requires 353kB of storage per mono second (i.e. 4 times more than 16-bit PCM audio at 44.1kHz.)
- DSK (Downstream Keying)
- A feature 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 color 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.
- DTRS (Digital Tape Recording System)
- An 8-channel digital audio tape recorder format utilizing Hi-8 videocassettes, developed by Tascam.
- DTS (Digital Theater Systems)
- A competing multi-channel audio format that encodes 1 to 7.1 channels of sound for playback on equipment with a DTS-compatible decoder. This lossy audio compression format is common in movie theaters, on some DVD-Video discs and laserdiscs. (See also DOLBY DIGITAL)
- DUB
- A duplicate copy made from one recording medium to another.
- DUBBING
- The action of adding or replacing audio, synchronized to a film or video picture. Virtually all modern motion pictures do some form of "dubbing" after the initial footage has been shot, to replace actors spoken lines or add sound effects. Audio dubbing is also a VCR feature allowing replacement of the audio signals on a previously recorded tape without disturbing the video signal.
- DUCKING
- The action of lowering the volume level of one audio segment in order for another simultaneous audio segment or live event to have more prominence.
- DUPLICATION
- Making multiple copies of a compact disc with a device which writes each CD one at a time.
- DVD (Digital Versatile Disc)
- A disc format jointly developed and agreed upon by Toshiba, Matsushita, Sony, Philips, Time Warner, Pioneer, JVC, Hitachi and Mitsubishi Electronics. DVD has become the universal format for high density audio and video compact discs utilizing higher data transfer rates. For computer applications, the disc is called DVD-ROM and for audio, DVD-Audio. Like the CD, it is available in a number of different “flavors”. Unlike the CD, it is available in a number of capacities ranging from 4.7GB to 17GB. (See DVD-Video)
- DVD-R (DVD-Recordable)
- The write-once DVD format standard. DVD-R discs are the DVD counterpart to CD-R discs.
- DVD-R DL (DVD-Recordable Dual Layer)
- The write-once DVD 2x capacity format standard. Also called DVD-R9, it is capable of holding 7.95GB of data.
- DVD-RAM (DVD-Rewritable Memory)
- A new type of rewritable compact disc that provides much greater data storage than today’s CD-RW systems. The caddy-mounted discs will initially provide 2.6GB per side on single or double-sided discs.
- DVD-ROM (Digital Versatile Disc-Read Only Memory)
- This read-only format supports discs with capacities from 4.7GB (enough for an MPEG-2 compressed full-length movie) to 17GB, and access rates of 600KBps to 1.3MBps. DVD-ROMs are backward-compatible with CD-ROMs.
- DVD-RW (DVD-ReWritable)
- Recordable and erasable media version of the DVD-R format standard. DVD-RW media can only be written and erased in a DVD-RW recorder, not in a normal DVD-R recorder, though a DVD-RW recorder can also record write-once media.
- DVD-Video
- A consumer DVD format for displaying full-length digital movies. DVD-Video players attach to a television like a videocassette player. DVD-Video utilizes a high quality digital video signal capable of nearly 500 lines of horizontal resolution. Unlike the DVD-ROM, the digital video format includes a Content Scrambling System (CSS) to prevent users from copying discs. This means that today’s DVD-ROM players cannot play DVD-Video discs without a hardware or software upgrade to decode the encrypted discs.
- DVD+R (DVD+Recordable)
- An incompatible competitor to the DVD-R format standard, this write-once DVD is being promoted by Hewlett-Packard, Philips and Sony.
- DVD+R DL (DVD+Recordable Double Layer)
- A write-once DVD 2x capacity format. Also called DVD+R9, it is capable of holding 7.95GB of data.
- DVD+RW (DVD+ReWritable)
- An incompatible competitor to the DVD-RW and DVD-RAM format standard, this rewritable DVD is being promoted by Hewlett-Packard, Philips and Sony. DVD+RW media can only be written and erased in a DVD+RW recorder, not in a normal DVD+R recorder, though a DVD+RW recorder can also record write-once media.
- DVE (Digital Video Effects)
- These effects are found in special effects generators which employ digital signal processing to create two or three dimensional wipe effects.
- DVI (Digital Video Interface)
- Multimedia standard for computer generated text and graphics merged in video production.
- DYNAMIC MICROPHONE
- A microphone that converts (transduces) acoustic energy into electrical energy using electromagnetic principles. Because of their simple construction, these mics tend to be very robust. In simple terms they operate on the same (but opposite) principle as a hi-fi speaker cone which accounts for them also being known as moving coil microphones.
- DYNAMIC RANGE
- The range, typically expressed in dB, between the loudest and softest sounds a sound source can produce without distortion.
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