[PlanetCCRMA] Re: Tascam US-122 audio problem

Andrew Burgess aab@cichlid.com
Tue Feb 22 19:42:01 2005

>> The short answer is no. It could be possible if the
>> cards are
>> synchronized (ie: running from the same clock) but I
>> don't know the
>> details. 
>I just done a bit of reading up on Jack and reached
>that conclusion when I read it was sample accurate. I
>guess that means only equipment with word clock can be
>used simulatiously. The only other thing I could think
>of is software based re-sampling of all audio. I don't
>know much about programming but I would guess that
>that would be fairly processor intensive.

If you are only correcting for clock accuracy and using the same sample rate
(e.g. two soundcards running at 48K) then you only need delete/insert a sample
every few 100,000 or million samples. Smooth it a little and it shouldn't be too
bad cpu-wise.

The problem I am finding is determining exactly how much the clocks differ.
I've been using gettimeofday(2) timestamps when the playback callback
is invoked but this seems to drift around alot.

I'm going to look for timestamps in ALSA next time I mess with it.