That's understood.
What is not completely understood by me is the technique in the paper,
and the very much related technique from the book.
How can this apply to arbitrary signals when it relies on sinusioids
seperated by several bins?
Also it seems I dont understand where the artefacts in my pitch shift
come from.
They seem to have to do with phases but it's not understood how exactly.
What is understood is that the neighbouring bins of a sinusoidal peak
have a phase -pi apart.
I dont see the effect of this though, they rotate in the same direction,
at the same speed.
But why is there no artefact of this kind when the signal is only stretched,
but not shifted?
Am 29.10.2018 um 19:50 schrieb Scott Cotton:
On Mon, 29 Oct 2018 at 19:12, gm <g...@voxangelica.net
<mailto:g...@voxangelica.net>> wrote:
Am 29.10.2018 um 05:43 schrieb Ethan Duni:
> You should have a search for papers by Jean Laroche and Mark
Dolson,
> such as "About This Phasiness Business" for some good
information on
> phase vocoder processing. They address time scale modification
mostly
> in that specific paper, but many of the insights apply in
general, and
> you will find references to other applications.
>
> Ethan
I think the technique from the paper only applies for monophonic
harmonic input -?
It picks amplitude peaks and reconstructs the phase on bins around
them
depending on the synthetic phase and
neighbouring input phase. I dont really see what it should do exactly
tbh, but
the criterion for a peak is that it is larger than four neighbouring
bins so this doesn't apply to arbitrary signals, I think.
I also tried Miller Puckets phase locking mentioned in his book The
Theory and Technique of Electronic
Music and also mentioned in the paper,
but a) I don't hear any difference and b) I don't see how and why it
should work.
From the structure displayed in the book, he adds two neighbouring
complex numbered bins,
multiplied. That is, he multiplies their real and imaginary part
respectivly
and adds that to the values of the bin - (Fig 9.18 p. 293).
Unfortunately this is not explained in detail,
I don't see what that would do other than adding a tiny
perturbation to
isolated peaks
and somehwat larger one to neighbouring bins of peaks?
I don't see how this should lock phases of neighbouring bins?
And again this doesn't apply to arbitrary signals?
No phase vocoder applies to arbitrary signals. PVs work for
polyphonic input where
- the change in frequency over time is slow; specifically slow enough
so that the
frequency calculation step over one hop can estimate "the" frequency
over the corresponding time slice.
- there is at most one sinusoidal "component" per bin (this is
unrealistic for many reasons), meaning
the time slice needs to be large enough and FFT large enough to
distinguish.
Note the above can't handle, for example, onsets for most musical
instruments.
Nonetheless, the errors when these conditions do not hold are such
that some are able to make
decent sounding TSM/pitch change phase vocoders for a widER variety of
input.
If you put a chirp into a PV and change the rate of frequency change
of the chirp, you'll hear the slow frequency
change problem. Before you hear it, you'll see it in the form of
little steps in the waveform
Scott
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Scott Cotton
http://www.iri-labs.com
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