Work without MIDI keyboard

It would be cool to extend this app, so that it works even without a MIDI instrument. For instance, you could sit in front of your computer with a **guitar**, and it would detect in real-time the pitches of the notes being played, and display them in a similar fashion.

Of course, you might want to do a separate screen saying "make sure your instrument is in tune, and that you are sitting in a quiet location", or something like that.