[sdiy] VCF caps in modern synths

[cheater cheater]

On Sun, Mar 28, 2021 at 4:47 PM Mattias Rickardsson <mr at analogue.org> wrote:
> I've never heard of aspers before, but it seems to refer to modulation in the lower audio frequencies (20-300 Hz) rather than harmonic distortion: https://community.sw.siemens.com/s/article/sound-modulation-metrics-fluctuation-strength-and-roughness

Your article talks about roughness in a very specific situation. See
the parallel thread for a paper by Hoeldrich which measures roughness
in full-band.

>> alternatively go to something like mV range and have a much more linear, tiny, capacitor - but at the cost of EMI adding a bunch of noise. Your choice. Fully-balanced synths anyone?
>
> since the self-modulation goes in the other direction for negative voltages, a straight-up balanced design wouldn't help much.

The capacitance is reduced (i.e. affected in "the same direction") for
both positive and negative voltages. The suggestion here was to have
very low voltages. The balancing would be used to remove EMI noise
from external interference. Not to cancel out the capacitance
reduction.

> Some research into the nonlinearities would be essential. Or why not go for C0G instead. :-)

C0G are specifically the ones that have the extreme variation in
capacitance based on applied voltage. They're the ones mentioned in
the article. So going for C0G is the worst thing you can do. I'm not
sure but I guess Colin's test was on a synth with NP0 capacitors or
ones that are built very similarly. Most ceramic capacitors with high
voltage ratings in a small package will be multi-layer, built just
like C0GNP0.