[Gta04-owner] Echo cancellation

[Radek Polak]

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.

I am leaving home until Sunday so i will not work on this now.

Regards

Radek


[1] https://github.com/radekp/gta04-gsm-voice-routing
[2] http://www.speex.org/docs/manual/speex-
manual/node7.html#SECTION00740000000000000000