Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site mtxinu.UUCP Path: utzoo!watmath!clyde!cbosgd!ihnp4!zehntel!dual!unisoft!mtxinu!ed From: ed@mtxinu.UUCP (Ed Gould) Newsgroups: net.audio Subject: Re: CD Reflections - 44.1k? Message-ID: <272@mtxinu.UUCP> Date: Fri, 18-Jan-85 15:36:55 EST Article-I.D.: mtxinu.272 Posted: Fri Jan 18 15:36:55 1985 Date-Received: Mon, 21-Jan-85 07:50:36 EST References: <15100001@hpfcmp.UUCP> <3411@mit-eddie.UUCP> <1420@hplabs.UUCP> <755@clyde.UUCP> <258@petrus.UUCP> Organization: mt Xinu, Berkeley, CA Lines: 25 > The Nyquist theorem is valid for ANY bandlimited signal, it doesn't matter > whether it is periodic or not. ... > ... Check out your communications > theory textbook on this one. > > Phil When I studied signal theory briefly about 12 years ago, there was a theorem stating that it was *impossible* to push more information through a signal than the bandwidth of the signal, e.g., one can't send more than k bits per second through a k Hz bandlimnited channel. Telephone voice-grade channels are 2700 Hz limited, filtering to allow signals only from 300 Hz to 3000 Hz. So how do 4800 and 9600 bps modems work over dialup circuits? (The telco carriers, by the way, are strict about bandlimiting their signals, since they frequency- multiplex them onto higher-bandwidth channels.) The answer seems to be that the theory that generated that theorem wasn't completely correct. Maybe the Nyquist theorem shouldn't be regarded as gospel, either. -- Ed Gould mt Xinu, 739 Allston Way, Berkeley, CA 94710 USA {ucbvax,decvax}!mtxinu!ed +1 415 644 0146