[Asterisk-Users] Echo cancellation

[Peter Zeltins]

> The library has several DSP features, including AGC, denoising, and
> echo cancellation.  These are all provided via integration with
> preprocessing from the SPEEX library.  I don't know if DAN allows you
> to turn on/off echo cancellation or not.  However, the echo
> cancellation code from speex is still very immature, and not quite
> there yet.  In particular, it is almost completely ineffective is AGC
> is also being used, because the echo canceller leaves a smaller
> residual echo in the signal, and the AGC then boosts up the residual
> echo to full volume.

Thanks for clearing this up - I was kinda curios what all those settings
are. Echo cancellation in my setup seems to increase echo (both with AGC
turned on or off), callers are reporting it sounds like speaking into barrel
or something.

> One thing you can do if you can't configure your card properly is use a
> "push to talk" feature.  This would need to be implemented in DIAX,
> although example code exists in other clients.  Basically, this looks
> for the user to press some "hotkey" before speaking (like a
> walkie-talkie"), and keeps audio muted unless the key is pressed.

That would be last ditch solution - not very convenient when I have to press
"talk" button every time. I've been able to reduce echo by decreasing
headphone volume and mike sensitivity, and turning "echo cancellation" off,
but it's still there a little bit. Also it seems to depend on PSTN end - if
I make a local call out to PSTN there is almost no echo, but calls to
mobiles (GSM) are plagued by echo to a much greater degree. Wonder why???

Peter