If I run a simple test (load the app, load a song, start the metronome, stop the metronome, then pause the app), I'm not seeing any processing being done with MobileSheets in the background. I do think there may be scenarios where Apple's audio framework could still be processing and causing battery drain though, so I'm going to add some code to force the current audio session to be stopped if MobileSheets is put in the background (if the option to play audio in the background is disabled) or the screen is turned off. We can see if that helps with the battery drain.
Mike
Mike