I have an Allen&Heath ZED428 soundboard with USB output, going to my brand new iMac. The Mac’s System Preferences indicates that the audio is coming through full-blast, maxing out the Codec input level. Yet Audacity reads NOTHING. Nada. Zero. Zip.
I have the Audacity settings set to the USB Audio Codec. When I have it set to a 2 Channel Stereo Input, I get just a tiny bit of sound on ONE channel. But for my purposes, I record on Mono, at which point I get NOTHING. Yet the System Preferences shows it coming in full-blast. Why is Audacity not getting anything at all?
As a fuzzy rule, the Stereo/Mono thing has to match. I thought one of my microphones was broken once because I had Audacity set to Stereo instead of Mono. The Mac built-in microphone appears both stereo and mono, leading you to think they’re all like that.
Audacity usually complains bitterly when you mismatch data settings. Try setting Audacity to 44100, 16-bit, Stereo. Audio CD settings.
Audacity > Preferences > Devices
Audacity > Preferences > Quality
See how that works.
Also make the exact same settings in /Applications/Utilities/Audio MIDI Setup.