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/usr/share/puredata/doc/5.reference/cpole~-help.pd is in puredata-core 0.46.7-3.

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#N canvas 619 313 610 611 12;
#X obj 54 95 osc~ 100;
#X msg 62 122 clear;
#X text 12 374 The transfer function is H(Z) = 1/(1 - aZ^-1).;
#X text 115 121 <-- clear internal state to zero;
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#X text 80 18 Stuff to test it:;
#X obj 241 106 cos~;
#X obj 77 227 cpole~;
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#X restore 459 488 pd test;
#X text 10 392 (Pd also provides a suite of user-friendly filters.
This and other raw filters are provided for situations which the user-friendly
ones can't handle. See Chapter 8 of http://crca.ucsd.edu/~msp/techniques
for an introduction to the necessary theory.);
#X obj 52 7 cpole~;
#X text 114 7 complex one-pole (recursive) filter \, raw;
#X text 132 98 <-- signal to filter (real part);
#X text 130 178 <-- signal to filter (imaginary part);
#X obj 84 177 sig~;
#X obj 115 202 sig~;
#X text 162 204 <-- filter coefficient (real part);
#X obj 145 224 sig~;
#X obj 53 249 cpole~ 0.9 0.4;
#X text 178 250 <-- creation arguments initialize filter;
#X text 206 266 coefficient (real and imaginary part);
#X text 14 283 The action of cpole~ is:;
#X text 11 325 where y[n] is the output \, x[n] the input \, and a[n]
the filter coefficient (all complex numbers). The filter is unstable
if/when |a[n]|>1.;
#X text 12 27 Cpole~ filters a complex audio signal (first two inlets)
via a one-pole filter \, whose coefficients are controlled by creation
arguments or by another complex audio signal (remaining two inlets).
;
#X text 171 148 <-- set internal state (real&imaginary parts);
#X msg 64 148 set 0.6 0.8;
#X text 190 226 <-- filter coefficient (imaginary part);
#X text 73 305 y[n] = x[n] + a[n] * y[n-1];
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#X text 16 563 see also:;
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#X text 255 507 real;
#X text 254 531 complex;
#X text 33 490 1-pole;
#X text 93 490 1-zero;
#X text 143 490 1-zero \, reversed;
#X text 58 474 summary of raw filters:;
#X text 140 563 etc.: user-friendly filters;
#X text 343 583 updated for Pd version 0.43;
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