Digital Audio Tape

storage, music (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.

(1995-02-09)