Adjusting Bluetooth microphone hardware volume
On some bluetooth headsets the microphone volume seems to be quite low. On some headsets I have it also seems the headset adjusts it automatically. It could be nice if Pipewire could adjust the source volume level.
In theory (see the HFP spec), the HFP command +VGM: XX adjusts the microphone volume. Tried to test this on a few headsets (JBL LIVE650BTNC, JBL Endurance RUNBT, Happy Plugs Air 1). All of them claim to support volume control in AT+BRSF. The first two don't issue AT+VGM=XX on startup. The last one issues AT+VGM=XX on startup, and apparently the +VGM: commands do have some effect, since on disconnect/reconnect the AT+VGM=XX sent by the headset shows the value previously set. However, on none of the headsets does the VGM value actually affect the volume of the recorded audio. (In contrast, +VGS: command adjusts the playback volume fine.)
There may be some feature on the headsets (echo canceling etc.) that disables control of the microphone gain. This would need to be figured out.