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Computing (FOLDOC) dictionary
Digital Audio Tape
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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
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.