Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!apple!usc!bloom-beacon!mit-eddie!mit-amt!mit-caf!grnberg
From: grnberg@mit-caf.MIT.EDU (David R. Greenberg)
Newsgroups: sci.electronics
Subject: Re: RS-232 for voice
Message-ID: <2958@mit-caf.MIT.EDU>
Date: 3 Aug 89 03:07:52 GMT
References: <9185@kean.mun.ca> <3999@cps3xx.UUCP> <8840@attctc.Dallas.TX.US> <6686@dayton.UUCP>
Reply-To: grnberg@mit-caf.UUCP (David R. Greenberg)
Organization: Microsystems Technology Laboratories, MIT
Lines: 20

In article <6686@dayton.UUCP> J. Deters writes:

>In article <8840@attctc.Dallas.TX.US> Steve Sampson writes:

>[paragraph about serially digitizing audio data paraphrased]
>>The quality is very acceptable.  I tried the circuit at 8 kHz and it
>>was just a little less than telephone quality.
>
>Only problem with this is the phone co. limits you to 3kHz bandwidth!
>
>There ain't no free lunch.

Fortunately, quadrature amplitude modulation (QAM) has been used to transmit
at 9.6 Kbps over the (slightly greater than) 3 KHz telephone bandwidth.
In QAM, the pulses used to transmit data are shaped to fit the necessary
bandwidth, but may have one of a discrete number of possible amplitudes
and phases and therefore may contain several bits worth of information
apiece.

- David