[Speex-dev] DPLL in aec samples

[Dario Andrade]

> 
> 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.

I agree. Unfortunatelly we're stuck with PC and Microsoft.

> 
> 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.

The thing is that in lots of cases we have different sound boards for
in/out.
USB microphones are very common nowadays, not to mention DV audio.

I wouldn't doubt if the same soundboard had different clock for in/out,
though. That would be a weird design, but what's not weird in computer
design these days?

Keep up with good work,
Cheers,
Dario Andrade

> 
> 	Jean-Marc
> 
> 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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> >