Here a standard demo/prototype of my tests using Lent Algorithm !

After 20 years of Keith Lent paper, remains a great choice :-)



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Sent From The Moon and Written With My Thumbs !

On Thu, Jan 17, 2019 at 6:31 PM robert bristow-johnson <> wrote:

> ---------------------------- Original Message ----------------------------
> Subject: Re: [music-dsp] Auto-tune sounds like vocoder
> From: "Eder Souza" <>
> Date: Thu, January 17, 2019 6:46 am
> To: "A discussion list for music-related DSP" <
> --------------------------------------------------------------------------
> > When I read the original patent US5973252A (Pitch detection and
> intonation
> > correction apparatus and method), in the vague description of how the
> pitch
> > shift is made, I wondered if everything seemed to be as simple as I would
> > be imagining...
> >
> > For pitch shift (auto Tune):
> > Just get the fracional period, use the fracional position period to cut
> off
> > or add periods whithout apply overlap and add (just splice and add/remove
> > in the exact period position, yeah this is why do you need a very strong
> > pitch detector, to join or discard in the exact period position to not
> get
> > clicks), this will expand or compress the signal, then now just resample
> > the signal to pitch shift (Ok now the formants go down).
> this is the standard kinda time-domain pitch shifting that goes by a
> variety of names: TDHS, maybe WSOLA.  it's what Eventide originally did
> (and i think what Autotune originally did).  when you splice out a period,
> that is time-compression (which speeds things up) and then for a pitch
> shifter, you have to resample that to slow down the time-compressed audio.
> that moves both the pitch and the formants down.  for upshifting you are
> spicing in an extra period (which is time-stretching) and then resampling
> that to speed it up which moves the pitch and formants up.  in this method,
> the cycles of the quasi-periodic waveform or stretched or scrunched in the
> resampling.  and in this method octave errors might not hurt you because
> all that means is you splice in or out two entire periods, instead of one,
> and it's still a reasonably glitch-free splice.  this is particularly the
> case for WSOLA, which is not directly worried about the pitch at all, but
> in Waveform Similarity (which *is* indirectly related to pitch).
> this is different than the Lent/Hamon method (sometimes called PSOLA), in
> which you window off a single cycle and call it a "wavelet" or a "grain".
> you do *not* stretch nor scrunch that wavelet or grain (unless you *do*
> wanna move the formants) but output the most current wavelet or grain,
> overlapping and adding, at the rate of the output pitch.  when upshifting,
> there is more overlapping and some grains will be used twice.  when
> downshifting, there is less overlapping and some grains will be skipped and
> not used.
> >
> > So I think that the current effect "Robotic or vocoded" happens when you
> > try change the formants (warping to original formants or just warping to
> a
> > new position).
> >
> > In the past I write the Keith Lent code to do Auto Tune(pitch correction)
> > and my results are cool...
> >
> > PS: I wrote to test the pitch detector described in the patent above
> (just
> > to proof of concept), and yeah this works great!
> well, i dunno where Autotune is now, but back in the '90s, i thought it
> sucked (the Wave Mechanics products, PurePitch and PitchDoctor were much
> better).  and Autotune back then did not use the Lent alg, so if there was
> a lot of shifting (like 3 or 4 semitones or more), Autotune definitely
> munchkinized the voice.
> --
> r b-j               
> "Imagination is more important than knowledge."
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