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

[Karl Hammar]

Giso Grimm:
> Maybe I am something missing, but what about the clock synchronisation?

There are works to make ieee1588 (PTP) into linux, [1-4].
That might help.

In [5], they seem to get <10us offset from a master within 2minutes
converging time. [6] gives a little different picture.

> It would be nice to allow synchronisation of several devices via the
> network connection. This transport medium typically has a lot of jitter
> (even an unloaded gigabit system can be above 50µsec), however, the
> jitter of typical AD/DA converters should be in the order of
> nanoseconds.

Do you (or anyone else) know the maximum allowable jitter useful for
audio?

> And in the case of several devices, how is it possible to
> compensate the absolute delay? All devices should be in phase, with a
> deterministic inter-device delay.

We have to think about that, I have no answer today.

> If it is only a single device it should be possible to use netjack: Then
> it behaves as a small host with its own sound card, and running jack
> with netjack_client (or whatever it ins called in recent versions). Any
> remote PC can run jack with the net backend to connect. Well, with
> netjack for jack0.116.2 the connection request is made from the other
> direction, in this case the open sound card, but connect requests could
> be triggered via OSC. And Netjack2 for jack2 seems to work completely
> differently.

So, it amount to write an alsa driver then?

Regards,
/Karl

[1] http://www.ixxat.com/evaluation-kit-linux-live-cd_en,24073,5873.html
[2] http://ptpd.sourceforge.net/
[3] http://www.estamos.de/blog/2009/07/01/linux-2-6-30-hardware-assisted-time-stamping-of-network-packets/
[4] http://bombadil.infradead.org/pipermail/ptpd/2009-November/000012.html
[5] http://ptpd.sourceforge.net/ptpd_2005_1588_conference_paper.pdf
[6] http://www.linuxclustersinstitute.org/conferences/archive/2008/PDF/Ohly_92221.pdf

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