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#X msg 714 337 print;
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#X msg 692 277 saturation \$1;
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#X text 301 49 test signal;
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#X text 127 126 Sine, f 8;
#X text 127 146 Sawtooth;
#X text 127 165 Noise, f 8;
#X text 144 104 Pitch;
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#X restore 126 162 pd test;
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#X text 31 630 see also:;
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#X text 729 651 updated for Pd version 0.52;
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#X obj 91 658 slop~, f 7;
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#X text 266 657 - unfriendly filters;
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#X text 859 14 <= click;
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#X obj 17 17 bob~;
#X text 57 18 - Runge-Kutte numerical simulation of the Moog analog resonant filter, f 69;
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#X text 89 239 float/signal - resonannce., f 64;
#X text 89 199 float/signal - resonant or cutoff frequency in hertz., f 64;
#X text 131 280 signal - filtered signal.;
#X text 89 91 float/signal - input to be filtered., f 65;
#X text 138 145 clear - clear internal state., f 58;
#X text 138 164 print - post internal state and parameters on Pd's window.;
#X text 139 316 NONE;
#X text 47 109 saturation <float> - set saturation point of "transistors"., f 71;
#X text 47 127 oversample <float> - set oversampling., f 71;
#X restore 765 14 pd reference;
#X text 653 424 Compatibility note: there was a bug in this module \, fixed for Pd version 0.52. YOu can get the (incorrect) pre-0.52 behavior by setting pd's compatibility level to 0.51., f 32;
#X text 812 535 old behaviour;
#X text 812 576 new behaviour;
#X msg 666 528 \; pd compatibility 51;
#X msg 666 570 \; pd compatibility 52;
#X text 46 537 The saturation parameter determines at what signal level the "transistors" in the model saturate. The maximum output amplitude is about 2/3 of that value. "Clear" momentarily shorts out the capacitors in case the filter has gone unstable and stopped working., f 78;
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#X text 325 188 Hz;
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#X text 474 238 (> 4 to oscillate);
#X text 266 631 - friendly filters;
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#X text 73 16 - Moog analog lowpass resonant filter simulation;
#X text 22 205 test input ->;
#X text 46 430 By default [bob~] does one step of 4th-order Runge-Kutte integration per audio sample. This works OK for resonant/cutoff frequencies up to about 1/2 Nyquist. To improve accuracy and/or to extend the range of the filter to higher cutoff frequencies you can oversample by any factor - but note that computation time rises accordingly. At high cutoff frequencies/resonance values the Runge-Kutte approximation can go unstable. You can also raise the oversampling factor to combat this., f 78;
#X text 764 336 print state;
#X text 338 136 resonant/cutoff frequency;
#X text 458 189 "resonance" (0-8);
#X text 43 366 input monitor ->, f 10;
#X text 390 375 <- output monitor;
#X text 69 63 This moog filter simulation is based on papers by Tim Stilson \, Timothy E. Stinchcombe \, and Antti Huovilainen (see [pd details] for pointers). The audio inputs are the signal to filter \, the cutoff/resonant frequency in herts \, and "resonance" (the sharpness of the filter). Nominally \, a resonance of 4 should be the limit of stability -- above that \, the filter oscillates., f 108;
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#X text 86 211 (sections 1 and 2 are a reasonably good introduction but the model they use is highly idealized.), f 69;
#X text 79 256 Timothy E. Stinchcombe \; Analysis of the Moog Transistor Ladder and Derivative Filters (long \, but a very thorough description of how the filter works including its nonlinearities), f 70;
#X text 81 133 Useful references:, f 63;
#X text 79 163 Tim Stilson \; Analyzing the Moog VCF with Considerations for Digital Implementation https://ccrma.stanford.edu/~stilti/papers/moogvcf.ps.gz, f 70;
#X text 79 72 The [bob~] object Imitates a Moog resonant filter by Runge-Kutte numerical integration of a differential equation approximately describing the dynamics of the circuit., f 70;
#X text 79 323 Antti Huovilainen \; Non-linear digital implementation of the moog ladder filter (comes close to giving a differential equation for a reasonably realistic model of the filter)., f 70;
#X text 79 395 The differential equations are \; y1' = k * (S(x - r * y4) - S(y1)) \; y2' = k * (S(y1) - S(y2)) \; y3' = k * (S(y2) - S(y3)) \; y4' = k * (S(y3) - S(y4)) \; where k controls the cutoff frequency \, r is feedback (<= 4 for stability) \, and S(x) is a saturation function., f 70;
#X text 64 26 Copied from README.txt;
#X restore 515 309 pd details;
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