Glossary of DVD Terminology "D"

DAC - Digital-to-analog converter. Circuitry that converts digital data (such as audio or video) to analog data.

DAE - Digital audio extraction. Reading digital audio data directly from a CD audio disc.

DAT - Digital Audio Ttape. A magnetic audio tape format that uses PCM to store digitised audio or digital data.

Data area - The physical area of a DVD disc between the lead in and the lead out (or middle area) which contains the stored data content of the disc.

Data rate - The volume of data measured over time; the rate at which digital information can be conveyed. Usually expressed as bits per second with notations of kbps (thousand/sec), Mbps (million/sec), and Gbps (billion/sec). Digital audio date rate is generally computed as the number of samples per second times the bit size of the sample. For example, the data rate of uncompressed 16-bit, 48-kHz, two-channel audio is 1536 kbps. Digital video bit rate is generally computed as the number of bits per pixel times the number of pixels per line times the number of lines per frame times the number of frames per second. For example, the data rate of a DVD movie before compression is usually 12 ´ 720 ´ 480 ´ 24 = 99.5 Mbps. Compression reduces the data rate. Digital data rate is sometimes inaccurately equated with bandwidth.

dB - See decibel.

DBS - Digital Broadcast Satellite. The general term for 18-inch digital satellite systems.

DC - Direct Current. Electrical current flowing in one direction only. Adopted in the video world to refer to a signal with zero frequency. Compare to AC.

DCC - Digital compact cassette. A digital audio tape format based on the popular compact cassette. Abandoned by Philips in 1996.

DCT - Discrete cosine transform. A mathematical process used in MPEG video encoding to transform blocks of pixel values into blocks of spatial frequency values with lower-frequency components organized into the upper-left corner, allowing the high-frequency components in the lower-right corner to be discounted or discarded. Also Digital Component Technology, a videotape format.

DDP - Disc Description Protocol. A specification for storing all the information needed to master a DVD (including CSS protection) on a DLT.

DDWG Digital Display Working Group - (see DVI).

decibel (dB) - A unit of measurement expressing ratios using logarithmic scales related to human aural or visual perception. Many different measurements are based on a reference point of 0 dB; for example a standard level of sound or power.

Decimation - A form of subsampling which discards existing samples (pixels, in the case of spatial decimation, or pictures, in the case of temporal decimation). The resulting information is reduced in size but may suffer from aliasing.

Decode - To reverse the transformation process of an encoding method. Decoding processes are usually predetermind by the encode / decode parameters.

Decoder - 1) A circuit that decodes compressed audio or video, taking an encoded input stream and producing output such as audio or video. DVD players use the decoders to recreate information that was compressed by systems such as MPEG-2 and Dolby Digital; 2) a circuit that converts composite video to component video or matrixed audio to multiple channels.

Delta picture (or delta frame)- A video picture based on the changes from the picture before (or after) it. MPEG P pictures and B pictures are examples. Contrast with key picture.

Digital Signal Processor (DSP) - A digital circuit that can be programmed to perform digital data manipulation tasks such as decoding or audio effects.

Digital video noise reduction (DVNR) - Digitally removing noise from video by comparing frames in sequence to spot temporal aberrations.

Digital - Expressed in digits. A set of discrete numeric values, as used by a computer. Analog information can be digitized by sampling.

Digitise - To convert analog information to digital information by sampling.

DIN - Deutsches Institut für Normung/German Institute for Standardization. (See Appendix C.)

Directory - The part of a disc that indicates what files are stored on the disc and where they are located.

DirectShow - A software standard developed by Microsoft for playback of digital video and audio in the Windows operating system. Replaces the older MCI and Video for Windows software.

Disc key - A value used to encrypt and decrypt (scramble) a title key on DVD-Video discs.

Disc menu - The main menu of a DVD-Video disc, from which titles are selected. Also called the system menu or title selection menu. Sometimes confusingly called the title menu, which more accurately refers to the menu within a title from which audio, subpicture, chapters, and so forth can be selected.

Discrete cosine transform (DCT) - An invertible, discrete, orthogonal transformation. A mathematical process used in MPEG video encoding to transform blocks of pixel values into blocks of spatial frequency values with lower-frequency components organized into the upper-left corner, allowing the high-frequency components in the lower-right corner to be discounted or discarded.

Discrete Surround Sound - Audio in which each channel is stored and transmitted separate from and independent of other channels. Multiple independent channels directed to loudspeakers in front of and behind the listener allow precise control of the soundfield in order to generate localized sounds and simulate moving sound sources.

Display rate - The number of times per second the image in a video system is refreshed. Progressive scan systems such as film or HDTV change the image once per frame. Interlace scan systems such as standard television change the image twice per frame, with two fields in each frame. Film has a frame rate of 24 fps, but each frame is shown twice by the projector for a display rate of 48 fps. 525/60 (NTSC) television has a rate of 29.97 frames per second (59.94 fields per second). 625/50 (PAL/SECAM) television has a rate of 25 frames per second (50 fields per second).

Divx - Digital Video Express. A short-lived pay-per-viewing-period variation of DVD.

DLT - Digital linear tape. A digital archive standard using half-inch tapes, commonly used for submitting a premastered DVD disc image to a replication service.

Dolby Digital - A perceptual coding system for audio, developed by Dolby Laboratories and accepted as an international standard. Dolby Digital is the most common means of encoding audio for DVD-Video and is the mandatory audio compression system for 525/60 (NTSC) discs.

Dolby Pro Logic - The technique (or the circuit which applies the technique) of extracting surround audio channels from a matrix-encoded audio signal. Dolby Pro Logic is a decoding technique only, but is often mistakenly used to refer to Dolby Surround audio encoding.

Dolby Surround - The standard for matrix encoding surround-sound channels in a stereo signal by applying a set of defined mathematical functions when combining centre and surround channels with left and right channels. The centre and surround channels can then be extracted by a decoder such as a Dolby Pro Logic circuit which applies the inverse of the mathematical functions. A Dolby Surround decoder extracts surround channels, while a Dolby Pro Logic decoder uses additional processing to create a centre channel. The process is essentially independent of the recording or transmission format. Both Dolby Digital and MPEG audio compression systems are compatible with Dolby Surround audio.

Downmix - To convert a multi-channel audio track into a two-channel stereo track by combining the channels with the Dolby Surround process. All DVD players are required to provide downmixed audio output from Dolby Digital audio tracks.

Downsampling - See subsampling.

DRC - See dynamic range compression.

driver - A software component that enables an application to communicate with a hardware device.

DSD - Direct Stream Digital. An uncompressed audio bitstream coding method developed by Sony. An alternative to PCM. Used by SACD.

DSI - Data search information. Navigation and search information contained in the DVD-Video data stream. DSI and PCI together make up an overhead of about 1 Mbps.

DSP - Digital signal processor (or processing).

DSVCD - Double Super Video Compact Disc. Long-playing (100-minute) variation of SVCD.

DTS - Digital Theater Sound. A perceptual audio-coding system developed for theaters. A competitor to Dolby Digital and an optional audio track format for DVD-Video and DVD-Audio.

DTS-ES - A version of DTS decoding that is compatible with 6.1-channel Dolby Surround EX. DTS-ES Discrete is a variation of DTS encoding and decoding that carries a discrete rear center channel instead of a matrixed channel.

DTV - Digital television. In general, any system that encodes video and audio in digital form. In specific, the Digital Television System proposed by the ATSC or the digital TV standard proposed by the Digital TV Team founded by Microsoft, Intel, and Compaq.

Duplication - The reproduction of media. Generally refers to producing discs in small quantities, as opposed to large-scale replication.

DV - Digital Video. Usually refers to the digital videocassette standard developed by Sony and JVC.

DVB - Digital video broadcast. A European standard for broadcast, cable, and digital satellite video transmission.

DVC - Digital video cassette. Early name for DV.

DVCAM - Sony’s proprietary version of DV.

DVCD - Double Video Compact Disc. Long-playing (100-minute) variation of VCD.

DVCPro - Matsushita’s proprietary version of DV.

DVD - An acronym that officially stands for nothing, but is often expanded as Digital Video Disc or Digital Versatile Disc. The audio/video/data storage system based on 12- and 8-cm optical discs.

DVD-Audio (DVD-A) - The audio-only format of DVD. Primarily uses PCM audio with MLP encoding, along with an optional subset of DVD-Video features.

DVD-R - A version of DVD on which data can be recorded once. Uses dye sublimation recording technology.

DVD-RAM - A version of DVD on which data can be recorded more than once. Uses phase-change recording technology.

DVD-ROM - The base format of DVD. ROM stands for read-only memory, referring to the fact that standard DVD-ROM and DVD-Video discs can’t be recorded on. A DVD-ROM can store essentially any form of digital data.

DVD-Video (DVD-V) - A standard for storing and reproducing audio and video on DVD-ROM discs, based on MPEG video, Dolby Digital and MPEG audio, and other proprietary data formats.

DVI (Digital Visual Interface) - The digital video interface standard developed by the Digital Display Working Group (DDWG). A replacement for analog VGA monitor interface.

DVNR - (see digital video noise reduction)

DVS - Descriptive video services. Descriptive narration of video for blind or sight-impaired viewers.

Dye polymer - The chemical used in DVD-R and CD-R media that darkens when heated by a high-power laser.

Dye-sublimation - Optical disc recording technology that uses a high-powered laser to burn readable marks into a layer of organic dye. Other recording formats include magneto-optical and phase-change.

Dynamic range compression - A technique of reducing the range between loud and soft sounds in order to make dialogue more audible, especially when listening at low volume levels. Used in the downmix process of multichannel Dolby Digital sound tracks.

Dynamic range - The difference between the loudest and softest sound in an audio signal. The dynamic range of digital audio is determined by the sample size. Increasing the sample size does not allow louder sounds; it increases the resolution of the signal, thus allowing softer sounds to be separated from the noise floor (and allowing more amplification with less distortion). Dynamic range refers to the difference between the maximum level of distortion-free signal and the minimum limit reproducible by the equipment.