[PD] [vcf~] with resonance?

Martin Peach chakekatzil at gmail.com
Wed Apr 25 23:40:48 CEST 2018


On Wed, Apr 25, 2018 at 12:46 PM, William Huston <williamahuston at 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:
> https://youtu.be/XA_WnyA7D6k
>
> 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~]
|
[*~ -0.9]  <-change this number to set resonance (between 0 and -1)
|
[clip~ -1 1] <- stops it from blowing up, but gives distortion with too
much feedback
|
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
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#N canvas 306 47 732 597 10;
#X obj 231 231 lop~ 440;
#X obj 231 274 lop~ 440;
#X obj 231 311 lop~ 440;
#X obj 231 351 lop~ 440;
#X obj 231 417 dac~;
#X obj 308 349 hsl 128 15 0 127 0 1 empty empty empty -2 -8 0 10 -4034
-1 -1 7700 1;
#X obj 305 373 / 128;
#X obj 230 388 *~;
#X obj 133 74 r~ \$0-fb;
#X obj 136 437 s~ \$0-fb;
#X obj 133 101 *~ -1;
#X obj 231 171 noise~;
#X obj 285 163 hsl 128 15 0 127 0 1 empty empty empty -2 -8 0 10 -4034
-1 -1 2300 1;
#X obj 282 187 / 128;
#X obj 232 204 *~;
#X obj 133 128 clip~ -1 1;
#X obj 197 84 / 10000;
#X obj 338 217 nbx 7 14 -1e+037 1e+037 0 1 empty empty empty 0 -8 0
10 -4034 -1 -1 229 256;
#X obj 197 54 nbx 7 14 -20000 0 0 1 empty empty empty 0 -8 0 10 -4034
-1 -1 -16960 256;
#X obj 103 221 vsl 15 128 0 100 0 0 empty empty empty 0 -9 0 10 -260097
-1 -1 12549 1;
#X obj 103 194 env~ 64;
#X connect 0 0 1 0;
#X connect 1 0 2 0;
#X connect 2 0 3 0;
#X connect 3 0 7 0;
#X connect 3 0 9 0;
#X connect 5 0 6 0;
#X connect 6 0 7 1;
#X connect 7 0 4 0;
#X connect 7 0 4 1;
#X connect 8 0 10 0;
#X connect 10 0 15 0;
#X connect 11 0 14 0;
#X connect 12 0 13 0;
#X connect 13 0 14 1;
#X connect 14 0 0 0;
#X connect 15 0 0 0;
#X connect 15 0 20 0;
#X connect 16 0 10 1;
#X connect 17 0 0 1;
#X connect 17 0 1 1;
#X connect 17 0 2 1;
#X connect 17 0 3 1;
#X connect 18 0 16 0;
#X connect 20 0 19 0;


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