Sound heavily distorted with conferencing mic-speaker

OK. I found the solution in case somebody else runs into the same issue. The sound distortion was caused by OVRLipSync plugin. I also found out how to fix this. So here comes the detailed solution for those who want to fix this in their projects.

It's the OVR Lip Sync Context script on the object with Audio Source that causes the distortion. It behaves like a audio effect and uses OnAudioFilterRead function to read the data from the AudioSource. But for some reason it also modifies the output data. The output data are perfectly fine until you try to play them on conference mic-speak device. I am not sure why. Obviously the Lip Sync won't work without it but here's the simple workaround.

In OVRLipSyncContext.cs find the OnAudioFilterRead method. Copy the sample array into a new separate array and at the end of the method, copy the saved array back to the sample array.

New class variable:
private float[] originalData = new float[256];

Method:
void OnAudioFilterRead(float[] data, int channels) {
int len = data.Length;
for(int i = 0; i < len; ++i) {
originalData [i] = data [i];
}

/*
... original function ...
*/

for(int i = 0; i < len; ++i) {
data [i] = originalData [i];
}

I know this makes LipSync a bit more CPU demanding, but I couldn't find a better solution.

PS: I know copying the sample array into a new separate array and performing lipsync on the new one would be less demanding but it gave me some wierd noises as well.