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From: sjc@angband.UUCP (Steve Correll)
Newsgroups: net.audio
Subject: Re: CD reflections
Message-ID: <39@angband.UUCP>
Date: Sun, 13-Jan-85 17:39:01 EST
Article-I.D.: angband.39
Posted: Sun Jan 13 17:39:01 1985
Date-Received: Wed, 16-Jan-85 04:35:12 EST
Distribution: net
Organization: S-1 Project, LLNL
Lines: 21

>  HIGH END FIDELITY - If we assume (and perhaps we shouldn't)  that all we
>  need to capture are complex signals composed entirely of symetrical sine
>  waves whose  highest  overtone is 20KHz, a (2x)  digitizing  rate in the
>  vicinity  of 40KHz just won't do.  For  example,  suppose we  digitize a
>  pure  20KHz   signal  at  40KHz,   and  happen  to   capture   only  the
>  zero-crossings.

I believe the Nyquist criterion requires the sampling rate to be *strictly*
greater than (and therefore not equal to) twice the highest frequency of the
information. You are quite correct that sampling a 20kHz sinusoid at 40kHz
might capture only the zero-crossings, and thus lose information, even in
an ideal system. But sampling at greater than 40kHz (even infinitesimally
greater) will in theory represent the 20kHz sinusoid without loss of
information.

Incidentally, here's some hope for lower prices. Laury's in Chicago and
Sam Goody's in Washington DC were recently selling the older Telarc CDs for
$10. Maybe in another year or so all CDs...
-- 
                                                           --Steve Correll
sjc@s1-c.ARPA, ...!decvax!decwrl!mordor!sjc, or ...!ucbvax!dual!mordor!sjc