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From: Jon.Fairbairn@computer-lab.cambridge.ac.uk (Jon Fairbairn)
Newsgroups: rec.audio.high-end
Subject: Re: data compression
Message-ID: <12101@uwm.edu>
Date: 13 May 91 12:58:23 GMT
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A while ago I made a posting "Why DCC should die," because I was incensed at
Philips' cynical timing of their announcement to coincide with the launch of
consumer RDAT in the UK.  I got hardly any response, probably because no-one
had heard of DCC at the time.  The posting is in the archives, so I shan't 
write the whole thing again, but here are some salient points.

1)
As has been noted, the DCC encoding (PASC) isn't lossless.  The idea is that
some sounds are inaudible because they are masked by others.  So the masked
sounds can be left out.  This relies on a naive (or perhaps willful)
assumption that says that what isn't normally heard will never be heard.  I
don't believe this.  I'm sure I'm not alone in having missed something ninety
nine times and then heard it on the hundredth.  OK, so maybe I needed to be
reading the score to hear it, but once I know what's in the score I can hear
it without reading it.   Did the listening tests in the design process go to
such lengths? I doubt it. I hate to think what PASC does to young people
learning to listen to complex orchestral music.

2) Very little has been said about reliability.  The more that data is
compressed the more information is lost when one bit is lost.  Unlike CD,
tape wears away, so the number of bits lost increases with time.  I think
RDAT uses more redundancy than CD, but even then tape wear will degrade the
sound eventually.  What happens to DCC?

3) Even heavily compressed, the DCC tapes can only record the same length as 
compact cassettes.   If you don't mind the effects of PASC (and for a lot of
music it really will be OK), then you can use it with RDAT format to get
eight hour tapes.

In case anyone thinks that I believe CD and RDAT are perfect, no I don't.

Jon (Jon.Fairbairn@cl.cam.ac.uk)

Please don't send me email if it has to go through ukc.uk -- that costs real
money to receive.