Time/Frequency Representations from an Artistic Point of View

Richard Dobson rwd at cableinet.co.uk
Thu Mar 4 07:08:59 EST 1999

I think the main sticking point is the 'without artefacts' issue.
Setting aside the visual transformations (which I gather IRCAM's
Metasynth is pretty good at), we (CDP+ Trevor Wishart) have got a lot of
mileage out of the Phase Vocoder (in fact,  a lot of IRCAM's SPV is
based on Trevor's original work). Artefacts can certainly arise, mainly
with regard to transients (ref the earlier thread on this topic) - the
trouble being, from your point of view, that composers such as Trevor
actually like them, so don't try too hard to eliminate them! I still
feel it should be possible to get cleaner performance from pvoc in this
respect, but I really don't have enough dsp nous to work out what has to

Various higher-quality commercial solutions have been mentioned on this
list (not least the prosoniq stuff); but as CDP is a non-profit-making
org, we can't afford to license such things, even if they were available
under those terms, so we are stuck with pvoc for the time being. And I
think there is sill plenty of scope compositionally with that. But for
'clean' timetretching, maybe other solutions are preferable.
Nevertheless, by a careful combination of pitch shifting and incremental
stretching, I have often been able to get very good clean results with
pvoc - it isn't a one-pass process though. Spectral morphing can be very
successful with pvoc (no stretching involved, just manipulation of
analysis channels), though, again, it is very rare to find a one-pass
solution to a trasformation task.

The criteria can vary so much from composer to composer (hate artefacts
v love artefacts), that a 'general' solution to the time/frequency issue
may just not exist.

Richard Dobson

> Michael Gogins wrote:
> One of the cool things you can do in computer music is time/frequency
> morphing. I am interested in it for several purposes, but the usual
> techniques don't satisfy me. I'd appreciate some feedback or
> discussion of the underlying issues.

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