[sdiy] HPFs and ADSRs

[David G. Dixon]

> > I also learned how annoying it would be to have only one envelope for
> > modulating both the VCF and the VCA, again from the MS-20.
> > After I finish my preamp/envelope follower, I guess my next project will
> > have to be a couple of SVFs and a couple of ADSRs.
> 
> Be aware that MS-20 highpass filter is quite different from SVF. Without
> resonance, it's 1-pole highpass and increasing resonance shifts it
> somewhat towards 2-pole.

Yes.  I was looking at Rene Schmitz's clone, but it's a pretty weird LP/HP
topology, with the second stage fixed in lowpass mode, and the resonance not
seeming to be hooked up to anything in highpass mode (is this a mistake on
the schematic?).  I wonder how different it would sound from an SVF, or even
a simple cascaded-OTA (or cascaded-VCA) 2P HPF?  Any thoughts?