You can reset all your Spectre meters to any desired audio input by following these simple steps:

  1. Quit Spectre, if open
  2. Go to System Preferences > Sound, go to the Input tab, and set your desired default audio input
  3. Delete your Spectre preferences file
  4. Re-launch Spectre

You should now find that Spectre has defaulted to the same audio input you set in System Preferences > Sound for all meters.