[Linphone-developers] Apparent echo issue when using HeadsetInOut with iOS

[Cameron Ambrose]

I was unhappy with the voice suppression processing in iOS as it was often 
turning my VoIP app into a half-duplex communication system.

So I deactivated it by changing

kAudioUnitSubType_VoiceProcessingIO to kAudioUnitSubType_RemoteIO

and commenting out

card->capabilities|=MS_SND_CARD_CAP_BUILTIN_ECHO_CANCELLER;

in msiounit.m

Since doing that, I am getting a very prominent echo where the audio from the 
POTS handset is reflecting back as if the liblinphone received audio was being 
directly fed into the mic. I have eliminated that feedback path as a 
possibility and the echoed audio is so clear, it almost sounds like it is 
directly coupled. The volume of the echo is also directly proportional to the 
headset volume. This effect appears to be limited to the HeadsetInOut Audio 
Route. When I use SpeakerAndMicrophone (and do my best to plug the iPad 
microphone) or HeadphonesAndMicrophone, I get no echo.

Is this an issue in iOS or is there something happening in the msio AudioUnit. 
Can anyone reproduce this issue? Any suggestions would be greatly appreciated.

liblinphone version :  3.6.99-233-gfa16748
iPad running iOS 6.1.3

Cameron