[LAU] Output to 2 sound cards simultaneously

Arnold Krille arnold at arnoldarts.de
Fri Sep 28 04:05:36 EDT 2007

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) 

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 

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 

> 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!

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