Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!clyde.concordia.ca!uunet!cs.utexas.edu!wuarchive!decwrl!ucbvax!pasteur!helios.ee.lbl.gov!ucsd!brian
From: brian@ucsd.Edu (Brian Kantor)
Newsgroups: comp.protocols.tcp-ip
Subject: Re: Xerox Etherphone experiments?
Message-ID: <10522@ucsd.Edu>
Date: 19 Dec 89 17:14:01 GMT
References: <8912190110.AA25330@ucbvax.Berkeley.EDU>
Reply-To: brian@ucsd.edu (Brian Kantor)
Organization: The Avant-Garde of the Now, Ltd.
Lines: 26

Enough people have written to me to ask about using the SparcStation to
transmit audio that I figured I'd better stem the flow by publishing the
note here.

First of all, the wiring diagram for the SS1 audio plug is in the 4.0.3
release manual that came with the SS1.  You need an 8-pin mini-din plug
which can be kinda hard to find, but it's used by Macintoshes so check
with your local toy computer store.  Note that the chip used in the SS1
is a telephony chip (it's an AMD AM79C30, designed to be the audio
processor in an ISDN voice phone) so it hasn't got a lot of input
gain.  You'll need a high-output microphone.  I used a carbon mic with
a battery and a small transformer.  I've also run the line-level output
of my desk stereo into the SS1; again, I used a small audio transformer
to avoid ground hum and frying the codec chip.

The software I used is

	rsh hostname cat \> /dev/audio < /dev/audio

which gives about a 1-second propagation delay on our local Ethernet; I
suppose this is related to an 8k buffer in either rsh or cat (I haven't
looked).  When it's running, I'm sending a packet just about once a
second, which is so little traffic that I stopped worrying about it
there.  For duplex communication, I suppose you'd want to use something
else that uses a smaller buffer to get less delay.
	- Brian