If your "instrument/note memories" thesis is correct, then it's not too hard to imagine that Brainr's initial setup would involve a calibration process to work

If your "instrument/note memories" thesis is correct, then it's not too hard to imagine that Brainr's initial setup would involve a calibration process to work out what your* particular mapping of sound memories is shaped like. * to give this putative "plays the music in your head" app a terrible name