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

Ken Restivo ken at restivo.org
Tue Nov 10 05:23:14 EST 2009


On Mon, Nov 09, 2009 at 01:42:00AM +0100, Karl Hammar wrote:
> Folderol:
> > On Sun,  8 Nov 2009 16:53:31 +0100 (CET)
> > karl at aspodata.se (Karl Hammar) wrote:
> ...
> > > Would a network connection solve that problem?
> > > In that case the DACs and ADCs could reside on an embedded computer
> > > and stream the sound data to/from the pc. And one could envision
> > > such little things near each mic and ethernet cables or possible wifi
> > > to the control room.
> ...
> > Ethernet looks interesting, and I know there is stuff out there, but
> > have no idea what latency and timing issues there may be. I would
> > imagine syncing multiple 'drops' to a stable clock might be problematic.
> 
> 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.
> 
> Would that be good scheme?
> 
> A simple ping here, has a rund trip time of 0.25 to 0.8 ms depending
> on end equipment.
> 

That's a fascinating idea.

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??!

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.

But the thought of a hardware audio interface that talks NetJACK natively, however, is really intriguing. Use OSC to control the interface....

Hmm. It'd be more than just a native Linux-supported audio interface, it'd be a JACK-specific audio interface.

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.

-ken



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