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

Karl Hammar karl at aspodata.se
Tue Nov 10 06:34:14 EST 2009

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.
> 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.
> 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?

> 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

4, refine the ADC part to satisfaction

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,


7b, add channels

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.


Karl Hammar                    Aspö Data               karl at aspodata.se
Lilla Aspö 148                                                 Networks
S-742 94 Östhammar          +46  173 140 57                   Computers
Sweden                     +46  70 511 97 84                 Consulting

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