[sdiy] Oscillator waveforms imperfections and formants

Rutger Vlek rutgervlek at gmail.com
Sat Jul 17 22:13:20 CEST 2021


Dear list,

Being an early Genesis fan I know the solo's of Tony Banks on the Arp Pro
Soloist very well, but only recently discovered the rather unique
architecture of this synth, and primarily it's capability to generate fixed
width pulse waves (the width is not a fixed percentage of the wavelength,
but really fixed in miliseconds).

Then I started reading about the theory of Pulse forming synthesis, and how
that was applied in the Variophon, for analog physical modelling of wind
instruments. The main message as I understood is that a fixed pulse width
waveform yields formants areas in its spectrum (independent of the
waveform's perceived pitch).

Then I had a look at my MI Braids oscillator and the impurities of the CSAW
oscillator model, modelled after de CS80 waveform. And I wondered about the
things:
1. Could the oscillator reset time of analog oscillators impose a high
frequency fomant area in the spectrum?
2. Assuming that the shape of the CSAW is modelling oscillator reset time,
shouldn't the artifact remain static in time, and independent of pitch? The
Braids model artifact changes proportionally to wavelength... Is that also
what a real CS80 would do?

Rutger

Op di 13 jul. 2021 07:11 schreef Roman <modular at go2.pl>:

> Or MIDECO if it only was available at the moment.
>
> Roman
>
>
> ---- Użytkownik Florian Anwander napisał ----
>
> Hello Francesco
>
> Am 09.07.21 um 16:09 schrieb francesco mulassano via Synth-diy:
>
> as a feature, however, I would really like to use the original scheme as
> much as possible and remain analog as possible (apart from midi, lfo and
> reverb)
>
> Then I would not care for MIDI->CV, because the stringmachines di not use
> VCOs.
>
> All you need is a MIDI to (61-folded) switch interface.
> You may do it yourself with an arduino,
> or use something like http://www.doepfer.de/mtc.htm
>
> Florian
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