[Linphone-developers] Echo and stuttering on Sony Xperia Z2 tablet

[Balder Mørk]

Hi,
Both linphone and my app using liblinphone suffer from echo and 
stuttering when using the built-in mic and speakers in the Sony Z2 
tablet. I'm using two identical tablets running the same version of 
linphone/liblinphone, and Android 4.4.4. My own app uses liblinphone 
2.3.2. I've tried enabling echo limiting and echo canceling, none of 
them, or just one of them. None of the four combinations solve the 
problem. The stutter seems to happen when the other party hears his own 
voice for a fraction of a second, so I'm guessing that's the echo 
limiter trying to eliminate feedback. Are there any good tips or 
step-by-step guides to eliminating such problems for tablets?

Here are some relevant lines from liblinphone startup.

Native android sound support available.
This device (Sony/SGP511/msm8974) declares it has a built-in echo canceller.
No AEC information available for model [Sony/SGP511], trying with 
platform name [msm8974].
Found AEC information for [Sony/SGP511/msm8974] from internal table
Sound device information for [Sony/SGP511/msm8974] is: builtin=[yes], 
delay=[0] ms
Could not set voip=on: err=-38.
Hardware output sampling rate is 48000
Hardware is known to have bugs at default sampling rate, using 16000 Hz 
instead.
Minimal AudioRecord buf frame size at 16000 Hz is 2048
Could not set voip=off: err=-38.
Card 'libmedia: android sound card' added
SDK version [19] detected
This device (Sony/SGP511/msm8974) declares it has a built-in echo canceller.
No AEC information available for model [Sony/SGP511], trying with 
platform name [msm8974].
Found AEC information for [Sony/SGP511/msm8974] from internal table
Sound device information for [Sony/SGP511/msm8974] is: builtin=[yes], 
delay=[0] ms
Card 'ANDROID SND (deprecated): Android Sound card' added

To me, it looks like the tablet has a built-in echo canceller, yet 
Hacks.hasBuiltInEchoCanceller() returns false. 
LinphoneCore.needsEchoCalibration() also returns false though, so I'm 
not quite sure what to make of this.

Also, LinphoneCall.isEchoCancellationEnabled() seems to ignore whatever 
I pass to LinphoneCall.enableEchoCancellation() during a call. It looks 
like I need to use the method in LinphoneCore to change the value.

I'm grateful for any tips or guides to solve my problem. Let me know if 
I should provide more information.


regards,
Balder Mørk