Little to No Sound on External Mic with Macbook M3

[psmacleod]

I have two Macbooks: an Intel 13-inch that's a few years old, and a recent 16-inch M3 Pro. They are both running Sonoma 14.6.1. When I use the Intel mac, with my Logitech HD Pro C920 webcam as the microphone, zoom calls work fine, and I see normal sound levels on Zoom's audio settings dialog. With the same camera plugged into the M3 pro, I get little to no sound on the webcam mic, it might just show one red bar, and if I really play a hard guitar chord I can hear a little attenuated blip when I do the "Test mic" procedure. Sound output is via an Audient EVO16. I usually use Original sound for musicians, because this is for guitar lessons, but the same thing happens with "Zoom background noise removal", and "Automatically adjust microphone volume" makes no difference.

The microphone in the webcam is selected as the system sound input, and I get normal sound bar levels in the system sound dialog. It also works fine with Skype and Google Meet. Is there something else that I can do to get this to work with Zoom?