music editing / decomposition
peter at crowther.demon.co.uk
Wed Sep 17 21:52:39 UTC 2003
> From: [...] Gary McGovern
> I've been told it doesn't exists but I can't believe it.
I'd be much more surprised if it *did* exist - most particularly for MP3.
> I've looking for software that will take an MP3 or similar and break it
> down into individual tracks (drums,guitar synth etc) and a score.
It's been done for single instruments; IIRC there's a hardware device out
there that will take a single, pitched note from eg. a guitar or flute and
turn the data into a MIDI stream. That's feasible - although even in this
case it gets confused about fundamental/harmonic on occasions. Take the
same guitar [bit difficult on a flute :-)] and play chords on it, and the
problem gets harder. Consider, for example, a power chord of root, fifth
and octave. The frequencies present in that get very confusing, as fifth is
1.5x root. Again, an analysis system that was expecting guitar might be
able to deal with this if the harmonics had the expected strengths; but a
more general system might reckon it was listening to an oboe with very
little of the fundamental, for example (the overtones on an oboe are
actually higher amplitude than the fundamental).
That outlines the problems for one instrument. Now consider the problems
with more than one. For example, I play in a folk band. We have two
melodeon [accordion] players, each playing a melodeon with four reeds per
note (so four sets of slightly detuned harmonics per note) via chorus units
(which detune again, so maybe 8-12 detuned sources per melodeon). One can
get some information from relative strengths of harmonics and, by
implication, stereo positioning - but it's hard. Much, though not all,
modern music is processed in this way to thicken the sound; it makes life
more difficult. Classical orchestral music has similar issues because of
multiple players of the parts, although something like a string quartet
might be a good starter for analysis.
MP3 makes all of this worse because it removes information. Stereo imaging
blurs; harmonic strengths change; phase information is lost. Actually, CD's
pretty bad for that too on the high frequencies - ask Ian Piumarta about the
difference between good vinyl on a Linn turntable and a CD! Ideally, one
needs more information rather than less.
Having said all of this, there's plenty of work in the field. An
interesting starting point might be:
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