Re: [sdiy] Additive VCO

[Roman]

My initial thouht is - there's no way it could work. But if you do it precisely, it may be interesting. Harmonics don't have to be exactly 2,3,4 etc. times the frequency of fundamental to make the sound interesting. Better yet, if they are slightly detuned, like 2.001, 3.001, 3.999, the sound will evolve and not be so boring static like, say Kawai K3.

I had an idea like this some time ago. I wanted to make several VCOs that are kept in tune by means of soft-sync. It may be hard to achieve for harmonics greater than, say, 20.

Another solution is to use waveshapers on fundamental triangle OSC. Split the slopes by 2,3,4,5, etc and make them wrap on split points. Easy to say, but circuitry may be complicated.

And if you can achieve pure sinewave of fundamental frequency, you can use Tschebyshev polynominals to make hundreds (yeah, tell me I'm crazy) of harmonics. That'll require one multiplier like AD633 and other minor stuff like opamp for each harmonic.

One last thought - if you want real harmonics, and want them all to stay in tune, use DSP and do it all digital.

Roman

---- Wiadomość Oryginalna ----
Od: "M.A. Koot" <makoot at gmx.net>
Do: synth-diy at dropmix.xs4all.nl
Data: Mon, 8 Mar 2004 00:25:18 +0100 (MET)
Temat: [sdiy] Additive VCO

>Hi everyone,
>
>I'm trying to design an additive-VCO, there aren't too many around, and
>that's why I would like to at least try it myself.
>My initial idea is by having one expo-converter, having the output devided
>over several Opamp-adders (to create the harmonic-offset). Those Opamp-adders
>have 2 inputs each then, one with the CVin, and one with the offset voltage.
>Each of those opamp outputs then go to seperate Sine-VCO's, one sine for
>each opamp-output.
>Then finaly mixing all the signals together, and that should be it.
>The things I'm troubling with though, is how many harmonics (i.e.
>Sine-VCO's) should I have at least to create a decent Additive VCO? I was thinking of
>about 16 Sine-VCO's. 
>Another thing that popped up is: How "correct" do they have to be?
>I can assume that if you want to create fairly true additive waves, with
>Fourier in mind, they have to be pretty accurate, increasingly with the
>harmonic-number probably.. But I wouldn't know how this would be in "real life". 
>I hope anybody could help me, does anybody maby already have some experience
>in this?.
>
>Thanks, cheers,
>Michiel
>
>-- 
>+++ NEU bei GMX und erstmalig in Deutschland: TÜV-geprüfter Virenschutz +++
>100% Virenerkennung nach Wildlist. Infos: http://www.gmx.net/virenschutz
>
>