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From: mraspuzzi@kl2116.DEC (Michael Raspuzzi)
Newsgroups: net.audio
Subject: Re: Lost bits in digital recording
Message-ID: <2547@decwrl.UUCP>
Date: Fri, 7-Jun-85 09:40:32 EDT
Article-I.D.: decwrl.2547
Posted: Fri Jun  7 09:40:32 1985
Date-Received: Sun, 9-Jun-85 02:21:08 EDT
Sender: daemon@decwrl.UUCP
Organization: DEC Engineering Network
Lines: 28

>3.  About digital recordings:  Even though CD-player blurbs talk about
>"error-correction", I'll bet there is none -  there's no time
>for it.  The real issue is, if there is an incorrect bit now and then,
>could you hear it ?  NO!  A single glitch in a digital record
>leads to white noise of very low amplitude, as I have verified by
>toying with artificial data sets simulating my experimental
>data.  You can't hear it.  Think of this another way.  Suppose
>Beethoven is playing along, and then one bit gets out of place.
>This causes a click of duration 20 microsec.  How sensitive
>would you be to that?  Not very sensitive.  These glitches 
>would have to be quite frequent to be annoying.  They're not -
>we're talking about rare events anyway, or else digital recording
>would never get off the ground to begin with (see point #1 above).
>Stop worrying and get some sleep.
 
Of course there is error correction! A popular misconception about the CD 
players is that they work like LPs. That is the "data" (music) is read and
sent to the amp (of course after it has been converted from digital to analog).
Most CD players do NOT work like that. The data is read off disc but is then
stored in memory. From there they are CLOCKED out using a vibrating quartz
crystal (usually). With all that time between read and clock out, this gives
the circuitry plenty of time for any error correction.
 
Mike Raspuzzi
DEC Software Specialist
ARPA: mraspuzzi%kl2116.dec@decwrl
...decwrl!dec-rhea!dec-kl2116!mraspuzzi
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