[Speex-dev] DPLL in aec samples

Jean-Marc Valin Jean-Marc.Valin at USherbrooke.ca
Fri Nov 11 13:12:26 PST 2005

OK, I'm tired of arguing. All those who think they're going to do AEC on
different un-synced cards, just go for it. However, please do not
complain and/or ask questions about that on this list. AEC is already a
hard enough problem when you have a sane sound setup that I see no point
in trying to do anything with drifting clocks.

As for soundcards with different clocks for in and out, I don't buy
this. It would cost the manufacturer an extra clock *just* to make
capture and playback out of sync? Now maybe Windows (or the card itself)
cannot start playback and capture at the same time. That actually
doesn't matter at all because it only introduces a *constant* delay
between the signals. 


Le vendredi 11 novembre 2005 à 15:00 -0300, Dario Andrade a écrit :
> May I still try to sync them using some kind of DPLL (digital phase locked
> loop) mechanism? Something like
> matching clocks and interpolating samples to try to sync them together?
> Do the interpolated samples get to be eligible for an aec in your opinion?
> Thanks,
> Dario
> > To everyone on the list: do *NOT* attempt to do echo cancellation with
> > signals sampled using different clocks. This will *NOT* work. Just a
> > 0.1% difference between the two sampling rates (it's sometimes worse
> > than that) means that the impulse response drifts by 8 samples every
> > second. There's just no way to efficiently track this.  Or at least no
> > way that doesn't involve something 100x more complex than what I have
> > now. So if you want to use two different soundcards, you should either:
> > 1) Have professionals cards connected with a clock sync
> > 2) Have an atomic clock in both cards
> > 3) Forget about echo cancellation
> > 
> > 	Jean-Marc
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