Thanks for tip, I had a brief look at this paper before.
I think the issue it adresses is not the problem I encounter now.
But it might be interesting again at a later stage or if I return to the
time domain pitch shift.
This is how I do it now, it seems simple & correct but I am not 100% sure,
it still sounds bad except for zero pitch shifts, pure timestretches
without pitch shift sound ok-ish though
Especially compared to the previous version with time domain pitch
shifting it sounds much worse.
1.loop through bins -------------
calculate input phase difference
subtract phase step of hop size of the original bin //=
phase-frequency-deviation
multiply by frequency factor
add phase step of hop size of the target bin
wrap into -pi...pi range
accumulate to bins phaseaccumulator
-------- end loop
2.loop through bins ------------
calculate spectral envelopes/formant correction
-------- end loop
3.loop through bins ------------
shift bins
-------- end loop
4.iFFT
for 2., the formant correction, you have to do this before the bin shift :
loop through bins -------------
smooth amplitude spectrum according to ERB scale or similar
----- end loop
loop through bins -------------
shift bins of a copy of the smoothed spectrum in oppsite direction
(1/freq factor)
// smooth again, or don't, or use MIPmapping )
calculate amplitudes * spectrale envelope 2 / spectral envelope 1
----- end loop
this seems correct (?) and does both, pitch shifting and time stretching
However, it doesnt sound good, it actually sounds kind of resonant, and
tinny
(noise elements seem to be converted to ringing sinusoids) and strange
except when the shift is 0, and also sounds better for downshifts then
for upshifts
also missing is a transient detection (in time domain?) to reset phases
to the original phases, and a noise / sinusiod detection, which might
improve things
part of the bad sound may just be the fromant correction, it sounds a
little bit like there were
two voices speaking in synch, another part is the low number of overlaps
example:
https://soundcloud.com/traumlos_kalt/freq-domain-pv-shift-test-4e-2f-4c-test-2/s-6SJ93
1024 @ 22050 kHz
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