Computer Dictionary of Information Technology

Digital Audio Tape

(DAT) A format for storing music on magnetic tape, developed in the mid-1980s by Sony and Philips. As digital music was popularized by compact discs, the need for a digital recording format for the consumer existed. The problem is that digital music contains over 5 megabytes of data per minute before error correction and supplementary information. Before DAT, the only way to record digitally was to use a video or a reel-to-reel recorder.

DAT uses a rotary-head (or "helical scan") format, where the read/write head spins diagonally across the tape like a video cassette recorder. Thus the proper name is "R-DAT", where "R" for rotary distinguishes it from "S-DAT", a stationary design that did not make it out of the laboratories. Studio reel-to-reel decks are able to use stationary heads because they can have wider tape and faster tape speeds, but for the desired small medium of DAT the rotary-head compromise was made despite the potential problems with more moving parts.

Most DAT recorders appear to be a cross between a typical analog cassette deck and a compact disc player. In addition to the music, one can record subcode information such as the number of the track (so one can jump between songs in a certain order) or absolute time (counted from the beginning of the tape). The tape speed is much faster than a regular deck (one can rewind 30 minutes of music in 10-25 seconds), though not quite as fast as a compact disc player. DAT decks have both analog and digital inputs and outputs.

DAT tapes have only one recordable side and can be as long 120 minutes.

DAT defines the following recording modes with the following performance specifications...

   2 channel 48KHz Sample rate, 16-bit linear encoding
   120 min max.
   Frequency Response 2-22KHz (+-0.5dB)
   SN = 93 dB   DR = 93 dB

   2 channel 44.1Khz Sample rate, 16-bit linear encoding
   120 min max
   Frequency Response 2-22KHz (+-0.5dB)
   SN = 93 dB   DR = 93 dB

   2 channel 32KHz Sample Rate, 12-bit non-linear encoding
   240 min max
   Frequency Response 2-14.5KHz (+-0.5dB)
   SN = 92 dB   DR = 92 dB

   4 channel 32KHz (not supported by any deck)

DAT is also used for recording computer data. Most computer DAT recorders use DDS format which is the same as audio DAT but they usually have completely different connectors and it is not always possible to read tapes from one system on the other. Computer tapes can be used in audio machines but are usually more expensive. You can record for two minutes on each metre of tape.