[PD] No "voltage-controlled" lowpass filter?

[Matt Barber]

> Hi,
>
> Is vcf~ (which is bandpass) the only available type of signal-controlled
> (smoothly-changing) filter? Doesn't the "voltage-controlled" version of
> lop~ and hip~ exist? Is it for a "mathematical" reason? (i.e.
> impossibility to implement in a relatively simple way)
>
> Or is it because it is trivial to "build" it in PD? If so, how?
>
> And if not, how would you "approximate" it, that is create in PD
> something similar to a simple low-pass filter whose cutoff frequency is
> controlled by a signal?
>


Attached are some abstractions I once threw together which should be
quite similar to the user-friendly ones.  Sorry for the very silly
help patch -- I hope I haven't made any stupid mistakes.

MB
-------------- next part --------------
#N canvas 195 68 319 395 10;
#X obj 38 34 inlet~;
#X obj 124 34 inlet~;
#X obj 38 253 rpole~;
#X obj 195 57 samplerate~;
#X obj 195 79 swap 1;
#X obj 195 102 /;
#X obj 195 34 loadbang;
#X obj 124 119 *~ 0;
#X obj 71 119 sig~ 1;
#X obj 71 180 -~;
#X obj 38 227 *~;
#X obj 38 278 outlet~;
#X obj 124 143 max~ 0;
#X obj 124 164 min~ 1;
#X obj 124 79 *~ 6.28318;
#X connect 0 0 10 0;
#X connect 1 0 14 0;
#X connect 2 0 11 0;
#X connect 3 0 4 0;
#X connect 4 0 5 0;
#X connect 4 1 5 1;
#X connect 5 0 7 1;
#X connect 6 0 3 0;
#X connect 7 0 12 0;
#X connect 8 0 9 0;
#X connect 9 0 2 1;
#X connect 10 0 2 0;
#X connect 12 0 13 0;
#X connect 13 0 9 1;
#X connect 13 0 10 1;
#X connect 14 0 7 0;
-------------- next part --------------
#N canvas 104 392 337 344 10;
#X obj 38 64 inlet~;
#X obj 94 64 inlet~;
#X obj 38 243 rpole~;
#X obj 185 88 samplerate~;
#X obj 185 109 swap 1;
#X obj 185 132 /;
#X obj 185 64 loadbang;
#X obj 94 149 *~ 0;
#X obj 38 292 outlet~;
#X obj 38 268 rzero~ 1;
#X obj 94 171 max~ -1;
#X obj 94 193 min~ 0;
#X obj 94 109 *~ -6.28318;
#X obj 93 227 +~ 1;
#X connect 0 0 2 0;
#X connect 1 0 12 0;
#X connect 2 0 9 0;
#X connect 3 0 4 0;
#X connect 4 0 5 0;
#X connect 4 1 5 1;
#X connect 5 0 7 1;
#X connect 6 0 3 0;
#X connect 7 0 10 0;
#X connect 9 0 8 0;
#X connect 10 0 11 0;
#X connect 11 0 13 0;
#X connect 12 0 7 0;
#X connect 13 0 2 1;
-------------- next part --------------
#N canvas 36 660 566 311 10;
#X obj 145 169 -~;
#X obj 281 165 -~;
#X obj 132 43 noise~;
#X obj 272 52 sig~;
#X obj 182 110 lop~;
#X obj 137 82 vcl~;
#X obj 263 96 vch~;
#X obj 305 93 hip~;
#X floatatom 337 38 5 0 0 0 - - -;
#X obj 159 213 print~;
#X obj 277 224 print~;
#X obj 195 178 bng 15 250 50 0 empty empty empty 17 7 0 10 -262144
-1 -1;
#X obj 330 179 bng 15 250 50 0 empty empty empty 17 7 0 10 -262144
-1 -1;
#X text 381 37 <- set cutoff;
#X connect 0 0 9 0;
#X connect 1 0 10 0;
#X connect 2 0 5 0;
#X connect 2 0 4 0;
#X connect 2 0 6 0;
#X connect 2 0 7 0;
#X connect 3 0 5 1;
#X connect 3 0 6 1;
#X connect 4 0 0 1;
#X connect 5 0 0 0;
#X connect 6 0 1 0;
#X connect 7 0 1 1;
#X connect 8 0 3 0;
#X connect 8 0 7 1;
#X connect 8 0 4 1;
#X connect 11 0 9 0;
#X connect 12 0 10 0;