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Path: utzoo!linus!philabs!prls!amdimage!steve
From: steve@amdimage.UUCP ( system admin)
Newsgroups: net.audio
Subject: Re: Digital Remastering
Message-ID: <283@amdimage.UUCP>
Date: Sat, 1-Jun-85 18:20:55 EDT
Article-I.D.: amdimage.283
Posted: Sat Jun  1 18:20:55 1985
Date-Received: Mon, 3-Jun-85 00:30:17 EDT
Distribution: net
Organization: AMDIMAGE, Sunnyvale, CA
Lines: 47

There seems to be a lot of talk about digital recording, and 
quite a few questions too. First, digital recordings and analog
recordings are both done on magnetic tape (yuck), at least 
until a CD-ROM appears in the recording studio. This means that 
the recording has a very limited life, due to tape stretching,
nearby magnetic fields, etc. The one thing that digital recordings
do to improve this is introduce a highly sophisticated error
correction technique known as the Cross Interleaved Reed-Solomon
Code. Without going into the details of what the code does, 
suffice it to say that the raw recording bit-error rate is
in the neighborhood of 10E(-4) to 10E(-5), and by using the
Reed-Solomon code you can reduce your bit-error rate to about
10E(-15). This is 10 orders of magnitude improvement.

As for parity calculations, they only yield a 50% improvement
in error *detection* (not the same as correction).  Even protocols
like XMODEM only yield about a 10E4 improvement in bit-error
rate, and this depends on the packet size transmitted.

Off onto another subject, thid discussion of CDs vs. LPs.
The one thing that most of the discussions on the net have 
failed to point out is the dynamic range of an analog recording
can *never* be as good as that of digital recording. This is because
of the compression involved to be able to keep your turntable's
cartridge from mistracking when very loud passages are played
back (1812 Overture cannons). The digital recording is still 
a matter of bits being interprets and your CDs laser can track
any bit pattern you throw at it. 

As an editorial in the June issue of Digital Audio observed,
the reason audiophiles aren't attracted to CDs is they like to
fiddle. They're not happy unless they've just rebalanced their
tonearm to perfection or replaced every capacitor in their preamp.
CDs don't have much of anything to fiddle with except the programming
features.

Anyhow, if you're really interested in the technical points of
CDs, I recommend the article "Communications Aspects of the
Compact Disc Digital Audio System" by J.B.H. Peek in the
Feb. 1985 issue of the IEEE Communications Magazine. Dr. Peek
works for Philips Research Labs.

Enjoy, 

steve

amdcad!amdimage!steve