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Using the right sound device

Ensure you have the correct audio device in your gsmopen (celliax) configuration file. Eg: plughw:0 is the first soundcard, plughw:1 is the second, etc. If your motherboard has a soundcard, and you add another one to be used by gsmopen, it will be plughw:1. You can check how the sound devices are named on your platform with: aplay -l | grep card it will give you the number to put on "plughw:N" in the configuration file.

Activate the sound device (volumes)

Check the volume for both play and capture, and check that capture is activated (press spacebar when alsamixer in capture mode): alsamixer -c[soundcard_number] -Vplay alsamixer -c[soundcard_number] -Vcapture we had good results with capt(31) autogain(on) speaker(75), your mileage can vary. Try to find the values that works best on your machine. If you get double digits (bounces) on incoming (eg: receiving) DTMFs, try to lower the capture volume. The lower the capture volume, the better.