DAB - Digital Audio Broadcasting. The new digital radio format that uses digital signals to carry both FM Stereo and AM radio stations to a suitable digital radio receiver. Currently available on SKY Digital and becoming readily available in the UK to people posessing a DAB radio tuner.  
DAC - Digital-to-Analogue Converter. Processes a digital signal and changes it to a analogue. DAC's are found in all digital source components such as CD, DVD and Minidisc. Separate DAC's can be added to most digital sources that can improve the resulting sound by reducing interference between internal components.  
DAT - Digital Audio Tape is a high quality recording format commonly used by professionals. Home DAT recording never really took off due to worries by the record industry that pirates would be able to make unlimited, perfect copies of commercial music software.  

DATA - Information in a digital form is called Data.

DATA REDUCTION - the process of reducing the amount of data recorded onto a digital media to increase the available space. This is generally done by removing data that the human ear can't hear, or by removing sounds that are masked by louder parts of the music. Some video data is reduced (or 'compressed') by only recording the changes between one frame and the next, rather that storing the entire frames as occurs in analogue picture transmissions.  
DCC - the original digital recording media that competed with Minidisc to replace cassette for home recording. Minidisc won the race and DCC is now rarely used. One of the good features of DCC was that existing analogue cassettes could be played back on DCC decks.  
DDD - found on CD cases to show that the music was recorded, mastered and stored digitally.  
dB (DECIBEL) - A measure of change in sound pressure. A change of 1 dB is just about audible, while an increase of +10 dB will greatly increase the volume. Sound volumes and pressure levels are rated in becibel values.  
DECODER - A component that contains hardware for decoding an raw signal and converting it into another format that can be used by particular equipment. DVD sound data passes through a Dolby Digital decoder to turn it into the separate analogue audio channels before being amplified, while UK digital satellite television signals pass through an MPEG2 decoder to reveal the sound and picture information.  
DIGITAL - The technology of recording, transmitting and storing information as digital data comprising of a series of ON and OFF signals. A digital signal takes up much less space than a traditional analogue signal, and the signal quality is not reduced when passed between different components. This is why high quality recordings can be made from CD to Minidisc or CD-R.  
DIGITAL OUTPUT - A socket for sending a raw, unprocessed digital signal to another component. A CD player may have a Digital Output for sending the data to an external DAC or Minidisc deck, while a DVD player will have one to connect to an external digital surround sound decoder. Uses either Optical (light) or Coaxial (electrical) cable.  
DIGITAL INPUT - The socket that receives digital data from another component through either an optical or coaxial digital cable.  
DSP - Digital Soundfield Processing features found on Home Cinema amplifiers and processors that change the properties of a sountrack to enhance the viewing experience and making the movie locations more realistic.  
DISCRETE - Used in Home Cinema to describe separate digital audio surround channels - Dolby Digital has 5.1 discrete channels of audio.  
DISTORTION - Unwanted interference from hardware or cables.  
DOLBY LABORATORIES - The company that developed the most common home and cinema sound formats in use today. Visit the Dolby Website from the Links Page.  
DOLBY B, C and S - Noise reduction systems found on tape decks. The background noise of a recording remains at a constant level regardless of the recording level of the soundtrack. The system records the soundtrack at a much higher level and deliberately reduced to the correct level on playback. This not only reduces the volume of the loud soundtrack but also the volume of the background noise making unwanted hiss harder to hear.  
DOLBY DIGITAL - Dolby Digital is cinema sound format using five separate channels of digital audio and five speakers plus a dedicated sub-woofer channel to create detailed and accurate surround sound. Often referred to as AC-3 5.1.  
DOLBY DIGITAL SURROUND EX - The new digital surround sound format first used on the new Star Wars movie in May 1999 in the USA. This format adds a rear centre speaker channel for more realistic placement of effects.  
DOLBY HX PRO - A system that allows higher frequencies to be recorded onto tape cassette allowing more audio information and therefore a more detailed sound.  
DOLBY SURROUND - The addition of a centre dialogue channel to a stereo soundtrack to create three channel surround sound from two channel stereo soundtracks in the cinema. Requires a Dolby Surround decoder to separate the extra channels. Sources such as VHS video tape, DVD, Laserdisc and some television transmissions carry the home cinema variant of Dolby Surround that also carries a fourth channel for a centre dialogue speaker. A Dolby Pro-Logic decoder is needed to decode home Dolby Surround software.  
DOLBY PRO-LOGIC - The system that decodes a four channel Dolby Surround soundtrack used in home cinema. A Pro-Logic decoder will also create realistic virtual centre and rear channels from any stereo source, even when no surround information has been encoded.  
DOLBY 3 STEREO - Used in the cinema and in some home cinema amplifiers to create virtual surround effects using just three front speakers, left, right and centre. Not as convincing as a true surround system using rear speakers, but the next best thing is space is limited for rear speaker placement.  
DROP-OUT - A brief loss of audio occurring due to a damaged CD, a poor quality analogue tape recording, or a tape head losing contact with the tape surface.  
DTS - Digital Theatre Systems' cinema sound format using 5.1 discrete audio channels for surround sound. Many consider DTS to be superior to Dolby Digital as DTS uses less Data Reduction leaving more of the original sound in the soundtrack. DTS-ES is a new 6.1 channel format featuring centre-rear speaker.  
DTS-EX - The latest version of the DTS format adds an additional matrixed rear-centre channel to cinema audio systems, similar to Dolby Digital Surround-EX.  
DTS OUTPUT - A special feature of the latest generation DVD players for use with the forthcoming DTS encoded DVD discs. Laserdisc's and CD's with DTS sound store the audio data as a PCM signal which means that they can be sent to a DTS decoder using a normal digital cable. DVD, however, stores DTS as a Bitstream signal that requires a different type of output dedicated to DTS.  
DUAL MONO - An amplifier that handles an two channel stereo signal an two separate mono signals to reduce internal interference and improve the resulting sound quality.  
DUBBED or DUBBING - when an alternative language has been added to a movie for foreign viewers, the soundtrack has been Dubbed.  
DVD - Digital Versatile Disc (NOT Digital Video Disc) - The new CD sized disc with a high capacity storage surface seven times larger than normal CD. Currently in use as a storage media for home cinema (DVD-Video) and Personal Computers (DVD-ROM), future uses include video games consoles (Playstation2) and high quality DVD-Audio. Recordable DVD has been developed as a likely replacement for CD-R, video cassette and tapes found in video cameras. DVD-Video has the best picture resolution currently available for the Home Cinema market with 500 horizontal lines compared with Laserdisc (400 lines) and VHS video (240 lines)  
DVD AUDIO - The next generation audio format that is competing with SACD to replace CD. It uses the higher storage capacity of DVD to increase the amount of recorded audio information. Faster DAC's will be used to decode the increased amount of information. It is possible for text and a limited amount of video to be included along side the audio.  
DVD-ROM - Software for Personal Computers stored on DVD rather than CD offering a minimum of 4700 MB and a maximum of 18800 MB capacity compared to 640 MB on CD.  
DYNAMIC RANGE - The range, specified in Decibels (dB) between the maximum and minimum signals that can be reproduced be audio equipment.