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Digital Audio Tape (DAT) (part 7)

Progress is happening so fast these days that a product hardly has chance to come onto the market before it is superseded, and that might happen to DAT, at least DAT for domestic consumption...

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Progress is happening so fast these days that a product hardly has chance to come onto the market before it is superseded, and that might happen to DAT, at least DAT for domestic consumption. I’ll never believe anything until I actually see it in the shops so I think it best that I accord the following the status of rumour:

Sony have announced a new digital recording system which is ostensibly for dictation machines only. It’s called the Micro DAT and uses a cassette smaller than even a conventional micro-cassette. ‘Large scale’ DAT is already working to incredibly fine tolerances so Sony have come up with a new system where the rotary heads throw the data onto the tape in identifiable blocks. On playback, the heads don’t attempt to gather the data in the correct order, but sweep up whatever information they come across in a more or less random fashion and store in a buffer from where it is reassembled back into the correct order. The recording format is 12 bit rather than DAT’s 16 and the sampling rate is only high enough to give a frequency response up to 15kHz (which is the same as FM radio). This level of sound quality would probably be more than a match for the typical personal stereo, and apparently machines could be produced very cheaply. Will this system see the light of day, or is it Sony’s implied threat that if we don’t accept DAT, they’ll keep throwing new formats at us until we succumb?

Rather less substantial is the rumour of Philip’s Digital Compact Cassette which will use a cassette either very similar or identical in form to a conventional cassette, but of course with a higher quality tape inside. Instead of a rotary head like DAT it uses an eight track stationary head to record a stereo signal at a rather lower level of quality. Will this format rise up and steal the digital rug from under Sony’s feet, or should Philips stick to making lightbulbs? We’ll have to wait and see.

DAT Modes of Operation

The DAT system was designed with several operating modes for different purposes. The standard mode is 2-channel, 16 bit, 48kHz sampling which was designed to give good audio quality while being incompatible with Compact Disc (to prevent digital copying). All machines support this mode, and will also play back in the pre-recorded tape mode, which is the same apart from 44.1kHz sampling. Some machines will also record in this mode, which is essential if you intend to make a Compact Disc from your master without going through either an additional analogue stage or a sampling rate convertor.

Other modes are not so well publicised, nor so useful: there is a 32kHz mode which is compatible with satellite broadcasting; a long play mode which samples at 32kHz and cuts the format down to 12 bits; a 4-channel mode which is also 32kHz, 12 bit. The final mode of operation is one where pre-recorded tapes are duplicated with a wider than normal track for increased reliability and speed of production at the expense of a reduced maximum playing time.

Although the 48kHz DAT format is perfectly good in itself, the 44.1kHz standard is necessary for full compatibility with Compact Disc. I would advise any studio owner to buy a machine that can record at both 44.1 and 48kHz, preferably without SCMS.

By David Mellor Thursday January 1, 2004
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