How to disable AGC (Automatic Gain Control) on iPhone?

[tmatsuo]

We're using react-native-live-audio-stream for recording breathing sound while wearing bluetooth headphones.
The recording itself seems to work, but the audio doesn't include most of the breathing sound, likely because of the AGC automatically applied by iOS. We'd like to disable AGC.

I'm trying to disable AGC with this patch:
https://gist.github.com/tmatsuo/57e5d2835ea6cc892c7ad0e071b341b6

However, it doesn't seem to work. The audio is still mostly silent.

Do you have any insights on how to achieve this?
Ideally it's great if we can modify this library and expose it as an option, but just hearing your thoughts would be helpful as well.

Thanks!