[sdiy] Driving SSI2144 freq control with PWM from a microcontroller

[Neil Johnson]

I wrote:
> Genuinely curious question: since you're driving a low-pass filter
> anyway, why not dispense with filtering the PWM and, assuming the PWM
> clock is way above audio, just drive the frequency control pin
> directly?

Mike Bryant wrote:
> Don't you mess up the effects of any log element that way ?

Possibly, but I don't see that as a problem - just add a(nother) lookup table.

> But definitely works for a linear synth.  My first microcontroller based synth (a Z80) in the early 80s used PWM for VCFs and VCAs.

Yup, the Australian ETI synths used switched-capacitor filters IIRC.

Neil