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