[LAU] open hw soundcard (was Re: status usb2 for sound)

Folderol folderol at ukfsn.org
Tue Nov 10 14:30:55 EST 2009

On Tue, 10 Nov 2009 12:34:14 +0100 (CET)
karl at aspodata.se (Karl Hammar) wrote:

> Ken Restivo:
> > On Mon, Nov 09, 2009 at 01:42:00AM +0100, Karl Hammar wrote:
> ...
> > > Lets say we have pc <> switch <> lots of network boards for a single mic
> > > PC could broadcast the clock to all micboards and the would hopefully
> > > arrive without noticeable skew or jitter. And the micboards could
> > > answer with that timestamp and the converted value. In this case
> > > the PC requests each sample one at a time from all micboards.
> ...
> > Instead of messing with USB2 protocols, design a board that
> > attaches a ADC/DAC to a microcontroller and shoves the raw floats
> > in and out over... Gigabit Ethernet??!
> Yes, or maybe raw ADC ints.

The idea or ints (or long ints if there is bandwidth and ADC accuracy)
appeals to me because there would be no additional latency.
> > I don't know if any of the cheap microcontrollers out there-- or
> > the free network stacks available for them-- could also handle the
> > speed of a large amount of audio.
> My near future project will use AT91SAM9260 (arm9, 32bit, 200MHz),
> and linux.

Sounds interesting.

> > But the thought of a hardware audio interface that talks NetJACK
> > natively, however, is really intriguing. Use OSC to control the
> > interface....
> I don't know netjack nor osc, but maybe someone else does, would they
> be good, lightweigth, and easy to implement for this?

I also don't know either of these, but I get the impression they
require serious computing power at both (all) ends. Raw sends and
receives seems more achievable to me. Sync everything to just one big
daddy computer that does all the real work.

> > Hmm. It'd be more than just a native Linux-supported audio
> > interface, it'd be a JACK-specific audio interface.
> Why not, maybe not cheeper, but open and hacker friendly.
> > The devil's in the details, though. Which DAC/ADC chip?
> > Which microcontroller? How much RAM? Which network stack?
> > Which preamp circuitry? How many channels?
> > Etc, etc. It's not a trivial project.
> Well start from the top:
> 1, test netjack and osc if they are things to use
>    (someone else has to come with the expertise for that)
> 2, the same with dummy audio values from the microcontroller to see
>    if its performance holds, I have an evaluation board that one
>    could do that on
> 3, the same add any ADC and an ext. preamp to get real sound

Are there any direct fast digital-ethernet modules on the market? Just
how fast can you get a serial stream to run through this?
> 4, refine the ADC part to satisfaction

The rules are
1 Layout
2 Layout
3 Layout

> 5, add preamp part
> 6, add power-over-ethernet so its just ONE cable
> 7a, start to miniturize, possible makeing it small enought to sit
>     directly on the mic,
>  or...
> 7b, add channels

I'd be more interested in that actually. I'd be thinking of not just
microphones anyway.

> I could do steps 2, 3, possible 4, 6 and possible 7.
> Nice, don't you think so?
> And, since ethernet is driven through transformers we won't have any
> ground loops, etc. On the negative side is that ethernet cables are
> more stiff than microphone cables, they have the wrong color ... it
> woun't look that good, and they are not that durable, same with its
> connector, but there are industrial version ethernet connectors one
> could possible use with more suitable cables.
> Regards,
> /Karl

Does anyone know if there are any ethernet based recording studios?
That could give a few clues about bandwidth, number of channels etc.

Will J Godfrey
Say you have a poem and I have a tune.
Exchange them and we can both have a poem, a tune, and a song.

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