Make sure that in the "System Settings Default Input" that INSTEAD of it being on default input, that either the "USB Mic" is the setting, or "Line-In" is the setting, depending on which you are using.
If you can't see your mic levels in your audio recording program on a Mac, go to your "Audio Midi" settings. You can find these if you go to- 1. Applications, 2. Utilities, 3. Audio Midi settings. Open this up.