I think I have a clue. It seems the audio distortion starts from applying [D113680](https://phabricator.services.mozilla.com/D113680). I suspect there are more [`AudioInputProcessing::NotifyInputData`](https://searchfox.org/mozilla-central/rev/be9c0ff754a04b32226b68aa014a8137ac29bd53/dom/media/webrtc/MediaEngineWebRTCAudio.cpp#1127) calls than [`AudioInputProcessing::ProcessInput`](https://searchfox.org/mozilla-central/rev/be9c0ff754a04b32226b68aa014a8137ac29bd53/dom/media/webrtc/MediaEngineWebRTCAudio.cpp#1229) so some audio/voice input data are dropped without being processing.
Bug 1725810 Comment 15 Edit History
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I think I have a clue. It seems the audio distortion starts from applying [D114807](https://phabricator.services.mozilla.com/D114807). I suspect there are more [`AudioInputProcessing::NotifyInputData`](https://searchfox.org/mozilla-central/rev/be9c0ff754a04b32226b68aa014a8137ac29bd53/dom/media/webrtc/MediaEngineWebRTCAudio.cpp#1127) calls than [`AudioInputProcessing::ProcessInput`](https://searchfox.org/mozilla-central/rev/be9c0ff754a04b32226b68aa014a8137ac29bd53/dom/media/webrtc/MediaEngineWebRTCAudio.cpp#1229) so some audio/voice input data are dropped without being processing.