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From: cmoore@amdimage.UUCP (chris moore)
Newsgroups: net.audio
Subject: Re: CD Reflections - 44.1k?
Message-ID: <42@amdimage.UUCP>
Date: Tue, 22-Jan-85 19:29:29 EST
Article-I.D.: amdimage.42
Posted: Tue Jan 22 19:29:29 1985
Date-Received: Sat, 26-Jan-85 07:15:33 EST
References: <15100001@hpfcmp.UUCP> <3411@mit-eddie.UUCP> <1420@hplabs.UUCP> <755@clyde.UUCP> <258@petrus.UUCP> <272@mtxinu.UUCP> <267@petrusTue, 22-Jan-85 19:29:29 EST
Organization: AMDIMAGE, Sunnyvale, CA
Lines: 26

> > 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?  
> > Ed Gould		    mt Xinu, 739 Allston Way, Berkeley, CA  94710  USA
> ... High speed modems work by sending
> more than one bit per transition on the line, e.g., the Bell 212 sends
> two bits per signal transition, which can therefore take one of 2^2 or
> 4 possible states....  

This brings up an often misundertood point - there _is_ a difference
between 1200 bps and 1200 baud.  The baud rate is the number of
signal transitions on the line.  By recording 2 bits per baud interval,
the Bell 212 modem sends 1200 _bps_ at 600 _baud_.  The V.24bis
2400 bps modem sends 4 bits per transition, thereby givin 2400 bps
at 600 baud.  600 baud is considered to be the practical limit for
full duplex communications, and 1200 baud is the limit for half duplex.
The bell 202 uses 1200 baud, but only one modem can transmit at a time.


-- 

"You can't get out backwards, you have to go forwards to go back"

 Chris Moore (408) 749-4692
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