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From: ww@macwcw.meediv.lanl.gov (William Ward)
Newsgroups: sci.electronics
Subject: Re: Digital Output On CD Players
Summary: Standards are available
Keywords: AES/EBU and S/P-DIF
Message-ID: <600@topgun.UUCP>
Date: 15 May 91 20:56:26 GMT
References: <1991Apr28.131743.3630@research.canon.oz.au> <7480020@hpfcso.FC.HP.COM> <1991May12.181457.10@cmkrnl.uucp>
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Organization: Los Alamos National Laboratory
Lines: 46

In article <1991May12.181457.10@cmkrnl.uucp> jeh@cmkrnl.uucp writes:
>In article <7480020@hpfcso.FC.HP.COM>, mll@hpfcso.FC.HP.COM (Mark Luce)
writes:
>> There are more and more of these types of products on the market. The idea
>> is to keep the signal in digital form as long as possible...
>
>good lord, man, we KNOW that much.  The question is, how do you go from the
>signal at the digital out jack to (for example) 2x16-bit parallel data?  

It been a while since the original entry was posted...I thought someone more
knowledgeable would have responded by now, so, I'll go ahead and through in my
$0.02 worth.

There are two standards for serial digital audio data exchange:  AES/EBU
(sometimes an XLR connector) and S/P-DIF.  I don't know where you would look
for the standards documents (the Audio Engineering Society would be one
starting point), but knowing the names should help.  I've seen an AES/EBU
document put out by Sony, I think, some 40 pages long with all the info about
the serial word format, error correction bits/schemes, etc..  At a recent
equipment exhibition, I saw a German company (HEAD Acoustics Gmbh) that was
showing a neat binaural processing system (with a dummy head stereo mic as
input and electrostatic headphones for output) that was based on a vanilla 286
machine that had NO A/D or D/A converters attached...they cleverly did all of
their processing using a DAT machine that is part of the package, exchanging
data over the digital ports with their own special hardware to interface (it
could be some 3rd party, I don't know).  National Instruments was displaying
their new DSP board (320C30-based) at the same exhibition, so I said to their
engineers, "Hey, you've got a serial digital input on that thing, why can't you
add some software to do digital audio I/O?"  I'm not sure if anything ever came
of that yet.  I think they could find a good market there.

If anyone is lucky enough to have a good DSP board in their PC, you could
probably get what you need with trivial hardware and some programming using
information from the standards.  But, for the real question, "How can I use the
data with hardware that costs less than my CD player?", I really don't have an
answer.  The standards may give enough info for a good hardware jock to come up
with a circuit, and there are sure to be VLSI chips that would help a great
deal, if you can find them.  But the DSP route is a good one because gives you
some options to answer the next question:  "OK, I've got parallel data coming
in at 176 kbytes/second...what do I do with it?"

Bill Ward

Disclaimer:  I am not an EE, so the above could be complete drivel.  My
knowledge of Head Acoustics and National Instruments products comes only from a
visit to the exhibit mentioned and a few brochures.