You can reset all your Spectre meters to any desired audio input by following these simple steps:
- Quit Spectre, if open
- Go to System Preferences > Sound, go to the Input tab, and set your desired default audio input
- Delete your Spectre preferences file
- 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.