I have a patch that generates the coefficients for [cpole~] according to the [vcf~]'s inputs and I was able to draw a freq response according to the cpole's z-transform.

it wasn't easy - I had help of a friend understanding the source code of vcf~ and in tjis forum someone solved all the z-transform issues for me. http://dsp.stackexchange.com/questions/17917/real-and-imaginary-frequency-responses-of-a-single-complex-pole

well, here's the patch for anyone who cares understanding vcf better. The patch is a mess and very dirty, but I will clean it up and put it in my computer music course examples soon.

cheers