I think it would be a great tool to implement a audio block/module that finds the most prominent signal frequencies in an audio signal. And I think autocorrelation can be used. Then it should be possible to detect several tones (ex. chords) and do analyzing of the content to do cool stuff... (octaves, harmonies, guitar synths etc.)
This might be used as a starting point: http://www.instructables.com/id/Reli...SP-Techniques/
I am really impressed by the work you do and the audio library is genius!