[Gta04-owner] Echo cancellation

NeilBrown neilb at suse.de
Tue Feb 21 12:12:16 CET 2012

On Mon, 20 Feb 2012 11:03:07 +0100 Radek Polak <psonek2 at seznam.cz> wrote:

> Hi,
> i have started working on echo cancellation in the gsm voice routing program 
> [1].
> Why do we need this? If you try e.g. QtMoko v40 you will notice that the 
> speaker and mic volumes are very low during call. I have been experimenting 
> with higher volumes, but then the other party starts hearing herself which is 
> very annoying. And current low volumes are usable only indoors. Btw same 
> problem was on Freerunner. Freerunner has special AT commands for this and it 
> was all handled by modem firmware then.
> So I have added two new defines in the voice routing program:
> If you enable first one, it will use simple algorithm which lowers mic volume 
> and increases speaker volume when the other party is speaking and does the 
> opposite when you are speaking.
> Second define uses speex library which has echo cancellation algorithm for VOIP 
> calls. You can find some info about it here[2].
> I have not tested it very much yet, but the walkie talkie algorithm seems to 
> work quite good. Using speex does not work for me yet - maybe i am doing 
> something wrong.

This is all good news - thanks.

Apparently there is echo cancelling code in the Linux kernel.
In drivers/staging/echo/

It is called oslec: open source line echo cancelling

I don't know how one uses it.

Could could include the same code directly in you program maybe, if other
approaches don't work.

Just FYI,

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