Re: [Phys-l] De-chording polyphonic music with software.

[John Mallinckrodt <ajm@csupomona.edu>]

Wow!  This is amazing.  Note that the software is evidently doing  
something much more difficult than a Fourier spectral analysis.  The  
implication is that it is determining which partials belong to each  
note being played simultaneously by a multiphonic instrument like a  
piano or a guitar and bundling them together so that each note can be  
transposed individually preserving its relative timbre without  
affecting the timbre of any other notes that are being played at the  
same time.  That does seem to me to be an impossible task in general  
because the problem is clearly underdetermined.  Consider, just for  
instance, playing a pair of notes separated by an octave and trying  
to determine which partials belong to which note.  It seems to me  
that this could only be accomplished by making some arbitrary--if,  
possibly, intelligent--decisions along the way.

I notice that the demonstrations are apparently limited to recordings  
of single instruments and I suspect that's no accident.  I'd be  
seriously blown away to hear piano notes altered within the context  
of a concerto!

John Mallinckrodt
Cal Poly Pomona

On Jul 18, 2008, at 9:12 AM, Bob Sciamanda wrote:

> 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:
>
> http://www.celemony.com/cms/index.php?id=dna
>
> Bob Sciamanda
> Physics, Edinboro Univ of PA (Em)
> trebor@winbeam.com
> http://www.winbeam.com/~trebor/
>
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