
The Shannon limit for voice lines is likely somewhere around 25kbps.
We are rapidly approaching it. The fastest affordable full-duplex
modems currently on the market are V32bis, which is 14400bps.


CELP manages to sound decent at 4800 bps.

In theory, if you built a speech recognition system that turned voice
into ASCII, and a perfect synthesis system on the other end that
sounded just like the person you were speaking to, you could get it
down to the information content of the speech.

With various kinds of LPC, you can get it down to 2400 bps or prehaps
even less, at which point it sounds horrible.

4800 bps is more than adequite for our purposes.

--
Perry Metzger		pmetzger@shearson.com