D1/D2/D3/D5>D1/D2/D3/D5:
Digital video recording and playback formats. The D1 and D5 systems use 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").

• D1: a component digital video tape recording format that conforms to the specifications set in the CCIR 601 standard
• D2: an 8-bit composite digital videotape recording format in which the composite video signal is digitized by sampling it at the rate of 4 times the frequency of subcarrier
• D3 an unofficial term for a composite digital videotape recording format invented by Panasonic
• D5: a component digital videotape recording format that conforms to the specifications set in the CCIR 601 standard; Panasonic format.

DAT:
Digital Audio Tape. A consumer recording and playback medium developed by Sony, maintaining a signal quality equal to that of the CD.

Data Rate:
The speed of a data transfer process, normally expressed in bits per second or bytes per second.

dB>dB (Decibel):
A unit for expressing the ratio of two amounts of electric or acoustic signal power, used for measuring audio and video signals. Technically, this is equal to 20 times the common logarithm of the voltage or current ratio.

DBS:
Direct Broadcast Satellite. The provision of broadcasting from a satellite directly to a consumer user, usually using a small aperture antenna.

DCT>DCT:
Discrete Cosine Transform. A form of coding used in most of the current image compression systems for bit rate reduction. It is the main part of JPEG and I-frame MPEG compression.

DDR:
Digital Disk Recorder. A high performance disk recording device used for realtime random-access recording and playback of digital video.

Decoder:
A device used to recover the component signals from a composite encoded source. Decoders are used whenever a component output is required from a composited or "encoded" source.

Decode:
To separate a composite video signal into its component parts.

Decompression:
To reverse the procedure conducted by the compression software algorithm to return data to its original size and condition.

Definition>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 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.

Delivery System:
The equipment used by end users to run or "play" an interactive program.

Demodulator:
An electronic circuit which separates the audio and video signals from the RF carrier frequency.

Density:
The degree of darkness of an image. Also, percent of screen used in an image.

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.

Desktop Video:
The application of non-dedicated personal computer systems to the performance of video editing and post production tasks.

Device Driver:
Software that tells the computer how to talk to a peripheral device, such as a videodisc player or printer.

Deltaframe>Delta Frame:
Also called Difference Frame. Contains only the pixels different from the preceding Key Frame. Delta Frames reduce the overall size of the video clip to be stored on disk.

Digital>Digital:
A method of signal representation by a set of discrete numerical values, as opposed to a continuously fluctuating current or voltage or where information is transferred by electrical "on-off" or "high-low" pulses, instead of continuously varying ("analog") signals. 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 communications technology generally permits higher speeds of transmission with a lower error rate than can be achieved with analog technology. As an analog signal is received and amplified at each repeater station, any noise is also amplified. A digital signal, however, is detected and regenerated (not amplified) and any noise is lost unless it corresponds to a value which the regenerator interprets as a digital signal.

Digital-to-Analog Converter (DAC, D/A, D-to-A):
A device used to convert digital signals to analog signals.

Digital Component:
Component signals in which the values for each pixel are represented by a set of numbers.

Digitalvideo>Digital Video:
A video signal represented by computer-readable binary numbers that describe a finite set of colors and luminance levels.

Digitization:
Process of transforming analog video signal into digital information.

DIN:
Deutsche Industrie Norme. An international connector standard. DIN connectors carry both audio and video signals and are common on equipment in Europe.

Dissolve>Dissolve:
A process whereby one video signal is gradually faded out while a second image simultaneously replaces the original one.

Distortion>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.

Distributionamplifier>Distribution Amplifier (DA):
A device which splits (distributes) one audio and/or video source to several audio/video device inputs. Typically, 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.

Dithering:
Blurred transition from one color to another in a computer picture.

Dolby>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.

Downstream Keying (DSK):
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 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.

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.

DSP:
Digital Signal Processor. A specialized, programmable CPU capable of performing high-speed mathematical processing. Ideal for use in compression algorithms.

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 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.

DTR:
Digital Video Tape Recorder, also call DVTR.

Dub:
A duplicate copy made from one recording medium to another.

DVD:
Digital Video Disk. Optical disks that contain full-length motion pictures for viewing on a personal computer or through a set-up box.

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.