[Gta04-owner] Echo cancellation
Dr. H. Nikolaus Schaller
hns at goldelico.com
Mon Feb 20 12:34:10 CET 2012
Am 20.02.2012 um 11:03 schrieb Radek Polak:
> i have started working on echo cancellation in the gsm voice routing program
> 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.
You can also play a little with the sound profiles of the Modem:
AT_OPCMPROF=3 Bluetooth Headset
This appears to modify the sidetone, noise suppressor and AGC
AFAIK, our sound codec (TPS65950) also has an AGC.
> 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.
> 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.
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