Voice communication at 8KHz sampling rate for all android device using OpenSL

Issue

I need to create a VOIP app and I'm using OpenSL ES. I need to capture and play pcm audio data at 8KHz sampling rate for all android devices. But, when i capture audio at sampling rate 8KHz and play it at the same time (voice communication), it produces noise and the audio is distorted for some devices like Samsung Galaxy S3, S4 etc. I know, there's a specific preferred sampling rate for each device and I want to know is there any workaround or any way to work with 8KHz sampling rate only without any distortion?

I tried increasing buffer size and many other things but failed to find an optimum and generic solution. I need audio data sampled at 8KHz for my encoder and decoder. I took re-sampling audio data before it is passed to my encoder or decoder as my second thought, but its not the solution i'm looking for.

I found CSipSimple used OpenSL and I went through some of their codes too. But, yet I couldn't find a solution and may be I failed to understand where to concentrate. I'm stuck here!

Solution

Here's how I solved my problem:

I was working on audio streaming for Android using OpenSL ES and this tutorial helped me a lot. I followed the instructions here and got the thing working. Then i found audio streaming with this approach doesn't work very well for some devices (mostly samsung devices). I tried many things like increasing buffer size, disabling environmental reverb etc etc. I found this answer very useful for improving streaming performance.

Finally, I found the audio is distorted because of theadlocks I had to use for synchronizing the buffer switches. Using lock free structure is suggested for better audio performance. Then I went with another approach of Victor Lazzarini which is a lock free Audio IO. This article of Lock-free audio IO with OpenSL ES on Android helped a lot to implement a lock free structure along with a better audio performance.

Answered By - Reaz Murshed