Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/17/84; site hplabs.UUCP
Path: utzoo!watmath!clyde!cbosgd!hplabs!piety
From: piety@hplabs.UUCP (Bob Piety )
Newsgroups: net.audio
Subject: Re: CD reflections
Message-ID: <1421@hplabs.UUCP>
Date: Mon, 14-Jan-85 11:03:22 EST
Article-I.D.: hplabs.1421
Posted: Mon Jan 14 11:03:22 1985
Date-Received: Tue, 15-Jan-85 01:42:48 EST
References: <39@angband.UUCP>
Distribution: net
Organization: Hewlett Packard Labs, Palo Alto CA
Lines: 25

> >  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.


If the sample signal has no frequency components above 20KHz, whether
naturally or filtered, then capturing only the zero-crossings of this signal
by sampling at 40KHz CAPTURES ALL THE INFORMATION THERE!!  If there were
perturbations on the 20KHz sinusoid, there would have to be a 
frequency-component there ABOVE 20KHz!  If there isn't, then ALL the
information has been captured.  NYQUIST WASN'T WRONG!


Bob