[sdiy] Formant filters, yay!

Kylee Kennedy kmkennedy at gmail.com
Tue Mar 21 23:53:26 CET 2017


Formants:

http://dood.al/pinktrombone/


Just use this site.
Kylee

On Thu, Mar 16, 2017 at 8:14 AM, Olivier Gillet <ol.gillet at gmail.com> wrote:

> > Incidentally, whether you sync the windowed waveform or not is one of
> the differences between the several flavours of this type of thing. Some
> places say you should, other places seem not to bother.
>
> Braids' "Z***" models are exactly that:
> https://github.com/pichenettes/eurorack/blob/master/braids/digital_
> oscillator.cc#L328
>
> You can play with the phase at reset, but also change whether the
> windowed waveform is scaled between -1 and 1 ; or between 0 and 1
> (with the corresponding adjustment for DC offset) - this will simulate
> whether the low frequencies of the window are eliminated or not.
>
> With a bit of work you could continually transition between the
> various filter responses. And with a bit of "waveform algebra", you
> can also simulate a filtered square or pulse...
>
> On the Cortex M3/M4 I use, it turns out to be more computationally
> expensive than synthesizing a band-limited oscillator filtered by a
> digital SVF - but it's still a fun technique. It doesn't produce
> exactly the same waveforms, since the envelope of the impulse response
> of a resonant filter is an exponential, not a linear function.
>
> One more thing: you have to do a bit of work to prevent aliasing. When
> the master oscillator resets (when its phase wraps around), the phase
> of the slave oscillator must be reset to master_phase /
> master_frequency * formant_frequency (not to 0). I have to update
> Braids with that!
>
> > Since then I've also done a much more specifically vocal version, again
> on dsPIC, using five sets of windowed sine waves to generate a full vowel
> spectrum. The nice thing is that you can add together five sine
> oscillators, then window the sum, and you get five tuneable formants and
> one basic pitch.
> > It sounded vocal, ish, but I wasn't that impressed. It made a series of
> AEIOU-type sounds when you twiddled it, but seemed like a lot of work for
> that result. I've had pretty similar sounds out of a couple of resonant
> filters.
>
> Individually control the shape / width of each formant's window; allow
> overlap to simulate very resonant formants, and you reach the next
> stage: FOF!
>
> But I agree that nowadays, these techniques do not really make sense
> since it's less computationally expensive to do things with a bunch of
> IIR filters or a lattice filter. A couple of updates ago, Braids'
> implementation of FOF got replaced by a band-limited pulse filtered by
> 3 parallel SVF and nobody seemed to notice :)
>
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