Thanks for testing that.
Just to confirm, you are using FMOD for the recording and playing of the sound? If so, you shouldn’t have to lock and unlock the sound. In the example, you are recording directly to the sound that is being played.
Another user had some issues with stuttering here: Vivox to Unity OnAudioFilterRead to FMOD programmer sound. Stutters/crackling - #15 by dougmolina. It may have some useful information.
Potentially, it may also be that the buffer is not long enough:
exinfo.length = (myFreq * sizeof(short) * myChannelsCount);
result = system->getRecordDriverInfo(DEVICE_INDEX, NULL, 0, NULL, &nativeRate, NULL, &nativeChannels, NULL);
exinfo.length = nativeRate * sizeof(short) * nativeChannels; /* 1 second buffer, size here doesn't change latency */
Hope this helps!