[PD] IIR Filter

[Miller Puckette]

There are two possible solutions.  One is to locally set the block
size to one, as in example G04.control.blocksize.pd in 3.audio.examples.
The other is to use the powerful vexpr~ object.

cheers
Miller

On Tue, Jun 27, 2006 at 03:39:47PM +0200, Sylvain Le Beux wrote:
> Hi list,
> 
> I am trying to implement an IIR filter which has the following equation :
> 
> Y[k] + a[1]Y[k-1] + a[2]Y[k-2] = X[k]
> 
> where X[k] is here a dirac to obtain the impulse response of the filter 
> (of course, first two calculations are set with null samples)
> I get stuck as I try to get the feedback loop of the filter and Pd send 
> me an "DSP loop detected" error message
> I know (as I query the Pd archive) there's a way to achieve it by using 
> block~ but I can't really understand how it works.
> I join my patch if anybody can't point me my mistakes or can improve my 
> implementation
> 
> Thanks for nay help
> 
> Sylvain

> #N canvas 667 376 465 288 10;
> #X obj 46 105 RII;
> #X obj 46 65 dirac~;
> #X floatatom 108 65 5 0 0 0 - - -;
> #X floatatom 151 65 5 0 0 0 - - -;
> #X obj 45 161 tabwrite~ RII;
> #N canvas 0 0 450 300 graph1 0;
> #X array RII 10 float 1;
> #A 0 0 0 1 0 0 0 0 0 0 0;
> #X coords 0 1 9 -1 200 140 1;
> #X restore 230 66 graph;
> #X obj 16 17 bng 15 250 50 0 empty empty empty 0 -6 0 8 -262144 -1
> -1;
> #X obj 16 40 t b b;
> #X msg 38 198 \; RII resize 10;
> #X connect 0 0 4 0;
> #X connect 1 0 0 0;
> #X connect 2 0 0 1;
> #X connect 3 0 0 2;
> #X connect 6 0 7 0;
> #X connect 7 0 4 0;
> #X connect 7 1 1 0;

> #N canvas 125 589 458 308 10;
> #X obj 62 137 z~;
> #X obj 62 111 z~;
> #X obj 62 183 outlet~;
> #X obj 91 112 *~;
> #X obj 62 44 inlet~;
> #X obj 108 44 inlet;
> #X obj 134 136 *~;
> #X obj 151 44 inlet;
> #X obj 118 72 +~;
> #X obj 62 79 +~;
> #X connect 0 0 6 0;
> #X connect 0 0 2 0;
> #X connect 1 0 0 0;
> #X connect 1 0 3 0;
> #X connect 3 0 8 0;
> #X connect 4 0 9 0;
> #X connect 5 0 3 1;
> #X connect 6 0 8 1;
> #X connect 7 0 6 1;
> #X connect 8 0 9 0;
> #X connect 9 0 1 0;


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