/usr/share/puredata/doc/5.reference/biquad~-help.pd is in puredata-core 0.47.1-3.
This file is owned by root:root, with mode 0o644.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 | #N canvas 327 119 689 397 12;
#X obj 15 12 biquad~;
#X msg 510 20 \; pd dsp 1;
#X msg 504 66 \; pd dsp 0;
#X obj 84 248 env~;
#X floatatom 84 275 0 0 0 0 - - -;
#X floatatom 15 110 0 0 0 0 - - -;
#X obj 15 246 env~;
#X floatatom 15 274 0 0 0 0 - - -;
#X text 13 297 Compare the value of the straight signal on the left
with the value of the filtered signal on the right.;
#X obj 84 215 biquad~ 1.41407 -0.9998 1 -1.41421 1;
#X msg 101 121 1.41407 -0.9998 1 -1.41421 1;
#X text 76 31 calculates the following difference equation:;
#X text 77 44 y(n) = ff1 * w(n) + ff2 * w(n-1) + ff3 * w(n-2);
#X text 77 60 w(n) = x(n) + fb1 * w(n-1) + fb2 * w(n-2);
#X text 18 76 Syntax: biquad~ fb1 fb2 ff1 ff2 ff3;
#X text 259 239 this biquad~ is a notch filter for fn = Pi/4;
#X text 265 258 (= SR/8 = 5512.5 Hz @44.1k);
#X text 91 14 2-pole-2-zero-filter;
#X text 113 99 list sets filter parameters;
#X msg 119 161 set 0 0;
#X msg 120 186 clear;
#X obj 15 170 osc~ 5512.5;
#X text 422 337 updated for Pd version-0.30;
#X text 189 163 set internal state;
#X text 187 185 ... or just clear it;
#X connect 3 0 4 0;
#X connect 5 0 21 0;
#X connect 6 0 7 0;
#X connect 9 0 3 0;
#X connect 10 0 9 0;
#X connect 19 0 9 0;
#X connect 20 0 9 0;
#X connect 21 0 6 0;
#X connect 21 0 9 0;
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