Re: [LAU] Output to 2 sound cards simultaneously

Am Freitag, 28. September 2007 schrieb Mark Constable:
> On Friday 28 September 2007, Lee wrote:
> > > As a baseline, say I started with this, where could I go
> > > from here to get an app (ie; Amarok) to play back out two
> > > soundcards at once ?
> > It's one of those things that seems like it should be easy but is in
> > fact nearly impossible. The problem is that the sound cards cannot be
> > kept in sync on the hardware level.
> I can appreciate for input that would be a critical
> showstopper but for output it's not such a big deal.

It is a big deal even for output. One soundcards output-buffer will be emptied
before the other (because of slightly different 48kHz) and this soundcard
will fire its Interrupt before the other. And then things become unstable...

Either you have (professional) soundcards that allow some kind of syncing via
world-clock or similar or:
If you do have a lot of time and a hand with the soldering-iron you can try to
sync several soundcards on the hardware-level by removing the quartz from all
but one soundcard and then solder cables from the one remaining quartz to the
other soundcards. This is best done with several similar (and cheap)
soundcards.

Then you still have the problem of all soundcards sending Interrupts where one
would be enough. So you would have to mask the interrupts from all but one
soundcard...

Only after that you can really start the asound-magic to couple the soundcards
together. At least before the soldering step above it will _never_ work
reliably.

> On 2007-09-28 14:43, david wrote:
> > Hmm, maybe you could play it to JACK and have JACK route it to both
> > sound cards?

Jack routing to two soundcards depends on alsa providing two soundcards as
one. Back to start you go!

Arnold

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