Wed Feb 17 23:10:04 EST 2016

VCF tweaks

Assuming that basic operation is correct, and that the weird HF
behavior is an impedance problem:

   How to tune the gains?

Once that is done, tune the impedances.

First step in tuning the gain, is to determine the small-signal
transfer function of the diode/capacitor network.

The point of interest is where the resistor/capacitor ladder reaches
180 degrees phase shift.  What is the gain at that point, taking into
account the input impedance of the diff-amp.

What I want, is to compute sensitivities:
- Impedances
- Component value -> other signal property

What I'm thinking though is to stop making this cerebral: bring back
the iterative tweaking idea.  Take the circuit, and translate it into
a C program that computes the simulation output.  No matter how much
time it takes, and plot it / play it.  Keep all parameter values
parametric, and tweak them in the same way as other RAI interactive
tweaks work.

Once that works, other sensitivities would be simple to calculate, as
derivatives of the whole function, or of some kind of accumulation.

It is all functional.  Keep it all functional and all that stuff
should just work.