[LAD] Playing Audio Over CAT5

Phil Frost indigo at bitglue.com
Mon Oct 1 14:12:48 UTC 2007

On Sun, Sep 30, 2007 at 11:55:30PM -0400, Stephen Sinclair wrote:
> >       I checked out netjack, but i dont think i want that, as i said i want
> > the audio from the router directly to the speaker through CAT5 and balun
> > assembly. Wat i am confused about is after the decoding how, wud i send it
> > over the ethernet and how wud analog signals travel over ethernet.
> Hello Tosif,
> I think what you are confused about is the definition of "Ethernet".
> Ethernet is a standard for sending digital bits of information through
> a wire.  Quite often we use CAT5 cables for this purpose, and it has
> become the standard to do so.
> Sometimes audio/video equipment also can make use of CAT5 cable,
> because it is a good twisted-pair standard with certain properties
> that make it attractive for sending signals with low noise.
> However, the fact that Ethernet and A/V equipment both use CAT5 cables
> does not mean that they are related in any way.  Your WRT is an
> Ethernet device, which knows how to encode and decode IP traffic for
> networking purposes.  However it has absolutely no analog connection
> to the CAT5 cable.
> So, I'm afraid to say, your idea of sending analog audio signals over
> CAT5 from your WRT will simply not work.  However, as suggested, using
> a good streaming program like netjack, you might be able to encode a
> digital audio signal and send it somewhere to a device that can decode
> it to analog.  But sending an audio signal along CAT5 straight from
> the WRT to the speaker is out of the question.
> I suggest looking into other solutions.
> Funny, this reminds me of the time when I was young and I tried to put
> a Commodore 64 digital tape into my living room tape player.  It
> sounded awful.  :)

Well, 10base-t and 100base-tx use only 2 of the 4 twisted pairs
available on a cat-5 cable. You could run 2 balanced or 3 unbalanced
analog audio signals over the same cable.

It's unlikely your hub or switch will pass these signals, and there is
the chance that your hub, switch, or NIC will get fried by them. If you
run the analog signal at line level and use active monitors, the risk is
probably small, but if you are running the cat5 between the amplifier
and the speakers, the voltages involved could potentially be much higher
and thus more likely to damage network hardware.

However, I think a more interesting project would be to send packets
from a plain computer with ethernet hardware such that the digital
packets it sends sound something like audio. The audio quality would be
horrible of course, but maybe if you read enough about the physical
encoding of data on ethernet networks, you could construct IP packets
which make music with maybe some simple analog filtering.

A similar project <http://www.erikyyy.de/tempest/> displays patterns on
a CRT which can be received on a nearby AM radio.

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