Technical Note: Bluetooth & Automatic Volume Adjustment

October 26, 2022

The symptoms for this are that:

  • You’re probably using MacOS,
  • and your bluetooth headset is automatically, seemingly randomly, muting and unmuting during calls,
  • but this muting is not reflected in the visible state of the call software,
  • leading you to believe that it’s a problem with the bluetooth headset itself.

The solution to this is to find and disable automatic microphone volume adjustment in the application.

I can reproduce the problem with the “Aftershockz” bone-conduction headset I’m quite fond of. While this problem was not easy to diagnose, the solution is one checkbox.

In more detail, many conference applications, Zoom and Teams in particular, have an “automatically adjust microphone volume” option somewhere under the hood. This will in some cases auto-adjust your microphone volume to zero, which in turn results in the operating system sending a signal to your headset telling it to mute the mic in the hardware. The hardware will do that, but this change of state will not be reflected in the zoom client.

And there’s just enough lag in this process, particularly if you’re trying to solve it by pushing the buttons on the headset that unmute you, that nothing quite happens with the immediacy that we normally expect from discernible causality. So you can end up with the software tricking you into the impression that your headset is in some bizarro state of hardware failure, which is not the case.

A quick google search suggests that this is an endemic problem at the intersection of “MacOS confcall apps (Zoom, Teams, bunch of others…) that try to be clever with volume management” and “Bluetooth devices that try to manage power aggressively”, and digging into the preferences to uncheck the “automatically adjust microphone volume” option solves the problem immediately.

Bluetooth has not worked right anywhere since Nokia died, I have no idea how any human who has not been heads down over this class of problems for decades would even start forming a mental model of what might be happening here much less how to fix it, and despite taking some pride in this there are times that I actively resent having to be really good at solving problems that shouldn’t exist in the first place.