Example: Just after 10 seconds, the 1st card in my example will be emitting
sample 441010 (44101 * 10), and the other card will be emitting sample
440300 (44030 * 10). This means that if the original audio has been recorded
at exactly 44100, the cards are already 0.016 seconds apart from eachother!
(44030 is an example of a really crappy clock chip on a card, but it's not
unheard of)
OK, so what is the workaround? Couldn't the card that is behind be made to catch up between songs? Couldn't every 1000th sample be dropped on the crappier card? Etc. In any case, in your example, the cards would be about 1 second out of sync for every 20 minutes of play time. In my use case, this really does not matter, as, again, the speakers are in different rooms. If the software can be made to cope (which it surely should be made to, if the problem is as prevalent as you describe) then afaic there is no problem.
Let me re-iterate: Without syncing the soundcards, this /will/ happen. This
is not a legend or some far-fetched possibility that people speak of but
which really never affects real life.
I touched on this above. So how do I sync the cards? Is there a specific method to do this with alsa?
Just imagine two wall-clocks. Can you really expect them to keep the exact
same time over years of continuous running without anyone re-setting them?
Cheers
Reuben
