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