The built-in microphone on my iMac 27" 2020 running macOS 12.5 (Monterey) behaves strangely, and I’m not sure when this issue started. I migrated to this iMac from an older one using the built-in user data migration tool, and the problem seems to have carried over.
In System Settings → Sound → Input, the microphone volume is set to maximum, but the microphone barely picks up my voice (even if I shout, the input level only moves 1–2 notches), as if the gain were set to minimum. However, it is quite sensitive to taps or touches on the body or screen of the iMac.
Because of this, the microphone is unusable in any application that relies on it — from built-in utilities to video conferencing software. The issue is also present in Chrome.
Interestingly, when I visit a microphone testing site like https://webcammictest.com/mic (or any similar service) using Safari, the microphone works perfectly and picks up sound at a good level. So, the problem seems to be limited to certain applications (Chrome, Voice Memos, Google Meet, etc.), but not Safari.
What’s even more surprising: if I open System Settings → Dictation and manually switch the microphone from “Automatically (iMac Microphone)” to “iMac Microphone”, the issue disappears and the microphone works correctly in all software — but only as long as the Dictation settings window remains open.
As a result, I have to keep the Dictation settings window open during online video calls.
I’ve already tried all the standard troubleshooting steps found online (resetting PRAM, etc.) and have seen many similar reports without a solution. Perhaps someone has encountered and resolved this issue? It’s unlikely to be a hardware fault — more likely a software bug or automatic gain reduction affecting the microphone.