DVD glossary

Data Area

Logical sectors in a volume containing descriptors, path tables, and files.

Data Bit

Information received from the host for storage or transmitted to the host after retrieval.

Data Field

A fixed length field containing the user information in a sector.

Decibel (dB)

Unit of measurement using a logarithmic scale to represent ratios of two values, A and B, calculated as log₁₀(A/B).

Defect Management

Replacement of unusable regions of media with either a subsequent block or a block in a separate spare area. Normally used for rewritable discs.

Deflection

Vertical, or axial, displacement error of a disc measured from a flat reference plane.

Descriptor

Structure that contains information describing a volume or file.

Deviation

Angular displacement error of a disc measured from the normal to a flat reference plane, also referred to as tilt.

Differential Phase

Use of phase, or time, differences instead of amplitude differences to provide a servo error signal.

Diffraction

Departure from perfect sharpness of the shadow edge of an illuminated object. Limits the minimum size of a focussed spot. See Huygens' principle.

Digital Sum Value (DSV)

Representation of the low frequency or DC component of a binary bit stream. The value +1 is assigned to a binary NRZ-I ONE and the value -1 is assigned to a binary NRZ-I ZERO. A cumulative sum of values is maintained for successive NRZ-I bits that may be used to select appropriate merging or channel bit patterns.

Digitize

Conversion of a sampled analog or continuous signal into a series of binary ones and zeros. Used for audio, graphic images, or physical measurements. Sampling frequency and number of binary elements affects accuracy of conversion back to analog form.

Directory

A file in a single extent belonging to only one directory hierarchy that contains contiguous records, each of which describe a file section or another directory.

Directory Hierarchy

One set of path tables and a multilevel set of directories defined by a volume descriptor and having a common character set and other properties.

Dropout

Significant loss of signal amplitude capable of affecting data and servo accuracy, usually related to a physical defect.

Duplication

Production of a copy using sequential, serial transfer of information elements from an original image to a duplicate. Low mastering and equipment costs and short preparation times are offset by low throughput, often limiting use to low volumes. Examples would be CD-R duplication from a digital master, or making copies of text using a line printer.

DVD

120 mm optical disc achieving higher data density through use of 650/635 nm lasers and, optionally, multiple information surfaces and/or layers.

Dye Polymer

Organic chemical that changes reflectivity when exposed to intense light of a particular wavelength.

DAC
Digital to Analog Converter. A device that converts digital pulses to analog signals.

Data Stream
See bitstream.

Data rate
The speed in which data is accessed/read, usually measured in kilobytes per second.

Data recorded area
The area of disc that can be used to store information. Other areas of the disc are reserved for lead-in, lead-out, clamping, and labels.

Data Search Information (DSI)
Along with PGCI, these packets are part of the 1.00 mbit/sec overhead in video applications (Book B). These packets contain navigation information which makes it possible to search and maintain seamless playback of the Video Object Unit (VOBU). The most important field in this packet is the sector address where the first reference frame of the video object begins. Advanced angle change and presentation timing are included to assist seamless playback.

DDP
Disc Description Protocol is a small file(s) that describe how to master a data image file for optical disc (DVD or CD). This is ANSI industry standard developed by Doug Carson and Associates. This information is used in the mastering process by the Laser Beam Recorders.

Decode
The process of decompressing a video clip and then converting its color space of from YUV to RGB.

Decoder
A device that decodes compressed audio (e.g. Dolby Digital) or video (e.g. MPEG-2) and produces the original information.

Decompress
The process of converting video and audio data from its compact form back to its original form for playback.

Deleted Scenes
Deleted Scenes are usually scenes that are removed from a program, for various reasons. Sometimes the scene was lousy, or was cut due to time restraints (or intrusive studio executives). Outtakes are usually goofs or bloopers that happened while filming the movie. Sometimes an outtake is considered a deleted scene as far as DVD packaging goes. Many times deleted scenes are reinserted into the film and the film is then called a "director's cut" or an "extended cut".

Delta frame
A frame containing only the data that has changed since the last frame. Delta frames are an efficient means of compressing image data.

Descriptive Video Service
The Descriptive Video Service is an optional language track designed for the visually impaired. It provides descriptive audio passages describing actions occurring on-screen.

Digital Comb Filter
To produce highly accurate Chrominance and Luminance signal separation, the chrominance and luminance signals are converted to a digital medium. This produces enhanced color purity and reduced dot craw.

Digitize
The process of converting an analog signal into digital data.

Digital Output
The majority of all DVD players will have at least a coaxial or optical output for sending the Dolby Digital bitstream to a Dolby Digital decoder. This decoder may be a stand-alone unit or built into a receiver.

Digital video
A video signal represented by computer-readable binary numbers that describe colors and brightness levels.

Dipole Speaker
A type of loudspeaker, designed to reproduce diffuse surround sound. This type of speaker has identical drivers that are 180 degrees out of phase with each other and radiate in opposite directions. This type of speaker is better suited for Dolby ProLogic surround sound than Dolby Digital.

Directory structure
For the video specification (Book B), this defines a common set of files that must be present on all DVD discs. Components include Root and Video_TS.

Direct View
A display device that uses tube technology, as opposed to front/rear projection technology.

Discrete Surround Sound
A type of surround sound where all channels are independent in their ability to play sound. Six channel surround sound (like Dolby Digital) can play six discrete channels to create an enveloping surround sound environment.

DLT
Digital Linear Tape, a high storage capacity (10-20 Gbytes) tape used as the input medium to master DVD. Media designated "type III" or "type IV" tapes are used for DVD

Documentary
Due to DVD's large storage capabilities, documentaries are created to give you a look at what went on behind-the-scenes while filming a movie. Some documentaries can be as long as the film itself, or only a few minutes in length (such shorts are often called "featurettes"). Most special edition will contain one or more of these behind-the-scenes features.

Dolby Digital (formerly AC-3)
This technology developed by Dolby Laboratories creates a digital bitstream of from one to six discrete source channels. When Dolby Digital is working in six-channel mode (5.1), five channels are full-frequency (20Hz-20kHz) while one channel is dedicated to low-frequency effects (LFE). Like Dolby Surround Pro Logic, it includes Left, Center and Right channels across the front of the room. Dolby Digital provides separate (discrete) left surround and right surround channels, for more precise localization of sounds and a more convincing, realistic ambience. Dolby Digital uses a lossy compression (around 12 to 1) algorithm and usually has a bit rate of 384 Kbps. Dolby Digital is the standard audio format for DVD and HDTV and is optionally supported on Laserdisc.
Dolby Digital decoder is required for playback, although all DVD players will "downmix" the signal into two-channel surround if you don't have the DD equipment. For more information - Dolby.com <http://www.dolby.com/>.

Dolby Digital EX
See 6.1 Channel Surround Sound

Dolby Digital THX EX
See 7.1 Channel Surround Sound

Dolby Pro Logic
An active matrixed surround sound technology that derives four channels (left, right, center, surround) from a two-channel source. The left, right, and center channels are full-frequency, while the surround channel is limited frequency and mono. Dolby ProLogic is the home theater equivalent of Dolby Stereo for films.

Dolby Pro Logic II
The next generation of Dolby Surround Pro Logic decoding technology. Dolby Pro Logic II can create a "simulated" 5.1 channel surround environment from a 4-Channel Dolby Surround signal. Pro Logic II is able to decode the thousands of existing Dolby Surround movies and TV shows already on the shelf, compatibly, and with enhanced image stability. The improvements in decoding techniques mean that the discreteness of the sound field elements are better-preserved in the decoding process than was possible with the now universally standard Pro Logic technology, developed in the mid 80s. Pro Logic II also incorporates special features for controlling the overall spatial dimensionality and frontal soundfield imaging that are particularly suited for autosound applications.

Downmix
The ability to playback mono, stereo, or multi-channel surround sound from an encoded soundtrack, depending on the playback system.

DTS Digital Surround
A high data rate, 5.1 channel surround sound technology developed by Digital Theater Systems. DTS Digital Surround is an encode/decode system that delivers six channels of master-quality, 20-bit audio. In the encoding process, the DTS algorithm encrypts six channels of 20-bit digital audio information in the space previously allotted for only two channels of 16-bit linear PCM. Then during playback, the DTS decoder reconstructs the original six channels of 20-bit digital audio. Each of these six channels is audibly superior to the 16-bit linear PCM audio found on conventional compact discs. The DTS digital surround sound uses data rates of 1.44 Mbps, nearly four times higher than Dolby Digital (384 kbps). It also uses a significantly less compression ratio of (3 to 1 vs Dolby Digital's 12 to 1).
In order to listen to the DTS soundtracks on DTS DVD titles you need a DTS compatible player and DTS receiver/decoder. If you don't have a player with a DTS digital output you can still use DTS titles but you won't hear multi-channel audio, just PCM stereo or 3 channel Dolby Digital depending on the title. All DTS compatible players should be compatible with Dolby Digital however.
For more information visit http://www.dtstech.com.

DTS Surround EX
See 6.1 Channel Surround Sound

DTS THX Surround EX
See 7.1 Channel Surround Sound

DTV
Digital Television. Applies to digital broadcasts in general and to the U.S. ATSC standard in specific. The ATSC standard includes both standard-definition (SD) and high-definition (HD) digital formats.

DVD
Digital Video Disc or Digital Versatile Disc. A high-density optical storage 6-inch disc capable of storing 4.7, 8.5, 9.4 or 17 gigabytes of data. DVD uses MPEG-2 video compression and Dolby Digital, or DTS audio.

DVD-5
Single-sided/single-layer DVD with 4.7 GB storage capability.

DVD-9
Single-sided/dual-layer DVD with 8.5 GB storage capability.

DVD-10
Double-sided/single-layer DVD with 9.4 GB storage capability.

DVD-18
Double-sided/dual-layer DVD with 17 GB storage capability.

DVD-Audio
Format of recording 16, 20 or 24 bit digital audio with a sample rate 44.1 - 192 kHz on DVD disc. DVD-Audio disc can also contain video, pictures or text.

DVD-R
Write-once type DVD-Recordable discs invented by Pioneer in 1998. This technology is used for master-disks recording.

DVD-RAM
DVD-Random Access Memory. Rewriteable type DVD disc with more than 2.6 GB or 4.7 GB (DVD-RAM Version 2) storage capacity per side supported by Panasonic, Hitachi and Toshiba. The main disadvantage of the technology - lack of backward compatibility, i.e. DVD-ROM drives and DVD players cannot read from DVD-RAM media.

DVD-ROM
DVD Read Only Memory. DVD-ROM is a version of DVD for computers, designed to replace the CD-ROM. It has the same capacity as DVD-Video that is far greater than normal CD-ROMs. To play DVD movies on a DVD-ROM drive you also need an MPEG-2 decoder board or software decoder.

DVD-ROM Features
DVD discs can be played on DVD-Video equipped personal computers. A new trend in the DVD world is to add computer-specific features to DVD-Video discs, that can only be played through DVD-ROM drives (PC Friendly Disks). These features can be screenplays, links to web sites (often called "web links"), advanced interactive games and text based information. These features are not accessible via DVD-Video players; one must have a DVD-ROM drive or DVD device with DVD-ROM capability.

DVD-RW
DVD-ReWritable. This format was developed by Pioneer and is partially compatible with modern DVD players and DVD-ROM drives. Can be used only for recording audio and video streams.

DVD+RW
Digital Versatile Disc plus Re-Writeable. This format is fully backward compatible with DVD players and DVD-ROM drives and can be used both for video recording and for data storage. Hewlett-Packard, Mitsubishi-Chemical/Verbatim, Philips, Ricoh, Sony, Yamaha and Thomson Multimedia support it. DVD+RW is still in development stage.

Dynamic Pan & Scan
DVD has the capability to pan across a widescreen image horizontally via instructions coded into the video bitstream itself. This would allow for the widescreen and the Pan & Scan versions to be contained in the same space as one version of the film. Currently, it is decided that players lack the ability to perform these calculations uniformly and smoothly, so this feature may never see the light of day.

Dynamic Range
The range between the loudest and quietest parts of an audio signal. TV sound is not very dynamic, with dialogue usually almost at the peak level of the signal. With film sound on DVD there is an large amount of headroom available for sounds louder that dialogue - up to 24dB. This is why the output level of a DVD player tends to be set low compared to that of a VCR.