[lug] Ethernet sound card - digital solution

[John Dollison]

Something I completely forgot about....
Many modern sound cards have Dolby 5.1 surround sound, and include a digital
output channel.  That digital signal can be hooked up to the input of most
modern stereo systems.  Since it's all digital, from hard drive to stereo
system, there should be 0.0% signal loss and distortion.

John D

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----- Original Message -----
From: "Peter Hutnick" <peter-lists at hutnick.com>
To: <lug at lug.boulder.co.us>
Sent: Thursday, September 05, 2002 6:20 PM
Subject: [lug] Ethernet sound card


I've been knocking a (possibly stupid) idea around in my head.  Like every
other Joe in town I want to be able to get music from my PC to my stereo.
I'm not real satisfied with any of the obvious solutions.  I think that
there is a better way.

Obvious ways and their problems:

1. Plug sound card output into stereo.
 - Less than ideal quality
 - Very limited distance between the PC and the stereo

2. USB "sound card"
 - Not much better run length
 - Not cheap >a buck and a quarter

3. Component MP3 player
 - expensive
 - limited to codecs/data rates/processing power of the box (or serious
hacking)
 - limited storage (yes, many are hackable)
   OR
 - tied to "server software" on a PC


My idea is to build something similar to a USB sound card, but use
Ethernet as the interface.

Something like:

 You play a song on the PC with your favorite player. (This could be as
simple as cating a file to the appropriate device file.)
 The sound driver breaks the audio down into chunks of a fixed size, wraps
an Ethernet frame around it (with the appropriate MAC) and flings them
onto the wire (at a fixed rate).
 The "sound card" grabs all packets with its MAC off the wire (I think
that this description is technically faulty, but it gets the point
across), strips the Ethernet frame and dumps the data into a FIFO.
 The FIFO streams into a DAC, which terminates into a pair of RCAs.
 If there is a stereo on the other end of the RCAs you get sound!

I am well aware that I have glossed over some non-trivial stuff here . . .
that's why I'm writing to the list!  Is anybody and EE type that can tell
me what the big problems with this are?  Is getting the data out of the
Ethernet controller and into a buffer feasible without using a processor?
If so I think that this could be build cheap around a DAC out of a broken
CD player!

-Peter


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