On Wed, Apr 25, 2018 at 12:46 PM, William Huston <williamahuston@gmail.com> wrote:
Yes, thanks for the detailed response, Ed!

I was hoping for some guidance for a bolt-on method for adding resonance to vcf~,
but maybe it's not so easy? or the wrong approach?

My error was thinking resonance was implemented with feedback.

I don't think you were wrong.
 
From this video, it looks like resonance is caused by a bump in the filter shape at the cutoff frequency:
The bump in the filter response is a manifestation of resonance caused by feedback (the electronotes paper explains it as moving the poles toward the imaginary axis as feedback increases).

An analog-synth-like filter can be made with 4 [lop~]s in series with a [send~] at the output and a
[receive~]
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[*~ -0.9]  <-change this number to set resonance (between 0 and -1)
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[clip~ -1 1] <- stops it from blowing up, but gives distortion with too much feedback
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on the input. The main problem is that the resonance value changes with filter cutoff frequency. Also Pd's number boxes don't have fine enough resolution; I use negative values from 0-20000 then divide by 10000 to get better control.

Martin