[sdiy] Innovative Oscillator Design (or not ?)

Roman Sowa modular at go2.pl
Tue Apr 9 10:42:11 CEST 2024


This is not doable with simple PWM. You talk about closed loop control, 
but then it will have to make huge corrections from cycle to cycle, 
leading to blurry, modulated waveform. Assuming 10kHz range, the low end 
using 8-bit PWM is like 40Hz, and next step is one octave higher. To 
make it work you have to constantly measure the VCO output voltage and 
not just the cycle period and adjust PWM multiple times during single slope.
The slopes of the triangle will not be smooth anyway, but steppy. The 
steps will have the slope the same as the highest frequency triangle, 
that is when PWM is at 100%.
PWM frequency is independent of VCO frequency, so at some frequencies 
you might expect intermodulation that will blend all over audio band.

Interesting idea and I don't hink I have ever seen it, although it 
highly resembles switched capacitor filter. Who knows, maybe there is a 
way to use commercially available switched cap filter ICs to work as 
VCO. But IMHO there is a lot more other simpler options to make VCO.

How about using common $2 Sigma-Delta DAC to control the integrator 
switch? It makes it so much easier. Wide range precise control of 24 
bits, every note is kept stable with single write to the DAC. The MCU 
only writes the DAC on pitch change, and possibly check tuning from time 
to time but it will not drift at all if you use proper integrator parts.

Roman

W dniu 2024-04-09 o 08:52, M J Bauer via Synth-diy pisze:
> Attn: Synth-DIY community...
> 
> A while back (2022), I had an idea for an oscillator design which could 
> be used in modular or hybrid synth's, but I have not yet tested the 
> concept. The oscillator may be digitally controlled or voltage 
> controlled, or both at once. I'm not sure if this technique has already 
> been tried and proven. I haven't seen any evidence of it, so I would be 
> grateful if anyone with a greater knowledge of the art can tell me if 
> this is a novel idea, or a concept that has appeared before. (See 
> attached summary.)
> 
> M.J. Bauer
> 
> 
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