Suppose you record from a single microphone, onto a single track, a
polyphony of music from several instruments. Here is software which will
disect the resulting single sound track into its "component pieces" and
allow you to manipulate the individual pieces. You could, e.g., change a
single note within a chord, even though your original recording gives you
only the single track waveform of the composite chord; you could
individually manipulate the sound from each guitar string given only the
composite chord waveform, etc. (You can tune your guitar in
post-processing!) The results appear to be quite striking . . . limitations
are to be expected. Take a listen.
For a demo go to this URL and click on the play button of the video shown in
center screen: