Wesley W. Terpstra wrote:
> I have two 4 channel cards.
> So far I have had success combining the two PCMs on one card like:
>
> pcm.c1b {
> type multi;
> slaves.a.pcm "hw:0,0";
> slaves.b.pcm "hw:0,1;
> ...
> Then things (like mplayer) can do surround sound on this card without
> problems. Switching to "hw:1,0" and "hw:1,1" also works, making the other
> soundcard do surround.
>
> However, the moment I try to use "hw:0,0" and "hw:1,0" together or any other
> combination which spans the two cards, I run into trouble. I was hoping that
> I would be able to combine these two cards to get 7.1 channels.
>
> There was some talk about synchronization issues between the two cards.
> I wonder if this might be the problem? The cards are identical, however and
> have dedicated IRQs, so I don't see why there should be a problem in this
> regard...?
These synchronization problems aren't related to interrupts.
Your two cards each use their own clock, so even if you tell them to
use the same sample rate, one will be slightly faster than the other.
If you want to synchronize multiple cards, you need ones that allow to
synchronize to an external clock. (Many USB devices actually are
synchronized to the USB clock.)
HTH
Clemens
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