[Gta04-owner] QtMoko audio state work

Radek Polak psonek2 at seznam.cz
Thu Jan 17 15:36:22 CET 2013

On Thursday, January 17, 2013 02:50:54 PM Neil Jerram wrote:

> On several occasions, on receipt of a real incoming call, I've just got a
> kind of distorted quiet growling noise
> instead of proper audio from the far
> end. 

For me the growling took just one 1 second - IMO it was some old recorded 
sample and after it finished the program was working normally.

The biggest problem was for me the volume - once i raised it, the echo 
cancelation was not working good. Maybe WebRTC has better algorithms then 

You can also try to play with alsa record/playback buffer sizes. The smaller 
the buffers are the smaller will be delay between recording and playing. And 
last thing that can be tried is speex AEC settings. Thats the line:

	speex_echo_state_init(256, 8192);

Basically the gsm-voice-routing should work like this:

rec UMTS -> SEND to AEC -> play on earpiece
rec MIC  -> cancel echo -> play on UMTS

"cancel echo" works by substracting "rec MIC - rec UMTS". It would be quite 
interesting to dump the recored sounds and also the AEC'ed sound to files and 
open them in some program to see how the sounds are shifted in time and to see 
how the AEC works.

IIRC speex has also another cancelling mode besides speex_echo_cancellation() 

Hmmm maybe i could start playing with it again - after one year i can find 
something new.



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