Problems with full duplex Audio

soeren at heisrath.org soeren at heisrath.org
Fri May 30 14:30:32 CEST 2008


Hi list,

I'm currently writing an application that can be used for either voip
or encrypted speech communications over gsm data connections (aka (HS)CSD).

When i tested it on the neo, I've encountered the problem that audio
recording while playing back doesn't work that well. It records data for
approx. one second, pauses for another second and then records
again. This problem only occurs when recording data and playing audio
data simultaneously - recording or playing alone works flawless. 

Now I wonder if that's a pulseaudio/cpu performance problem, a problem with
the audio chip used in the neo or my mixer settings [0]. Pulseaudio's cpu
usage is around 20% pacat consumes another 20%-30% according to top or ps.

When testing it with the "pacat" application from the pulseaudio project
website [1], you can (probably) reproduce that error - try the following:

  pacat -r | pacat -p

(If you can't or don't want to compile it, get it from [2])

Doing that test with netcat over the usb ethernet device from my host to
the moko and vice versa showed that the problem only occurs in the
recording stream while playback (on the moko side) works just fine.

Has anybody else tested full duplex audio on the neo yet? Could any of
the freerunner owners (if there are any) try that pacat-test - if it
works on the freerunner, that would mean that my gta01 is just too slow...


Thanks for any advice

  - Soeren

__
0 - http://soeren.heisrath.org/stuff/mokomixersettings
1 - http://0pointer.de/lennart/projects/pulseaudio/doxygen/pacat_8c-example.html
2 - http://soeren.heisrath.org/stuff/pacat
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