[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:
> 
> USE_WALKIE_TALKIE_AEC
> USE_SPEEX_AEC
> 
> 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
 http://www.rowetel.com/ucasterisk/oslec.html

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,

NeilBrown
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