[Speex-dev] AEC with different soundcards

[Mark Pietras]

I've been testing the AEC and have experienced it working on one sound card, and not working when using different cards for capture/playback so I know it's a real problem.  And yes I know the documentation says it won't work "regardless of what you may think."  I'm the inquisitive type; I'm looking to understand just what exactly is happening here.

One discussion in the archives: John Ridges says "The AEC can only cancel linear changes to the audio path, and so the AEC never converges." I guess I don't understand the "linear changes" part of that statement.  Seems to me that the "perfect" echo cancel position could basically land "between" samples, and given that the AEC will adapt to changes over time anyway, I guess I just don't understand why it matters if the clocks drift.  That is, why doesn't the "adaptation" just drift too?  Hoping someone could explain in layman's terms... Thanks, Mark.
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