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117 lines
2.1 KiB
117 lines
2.1 KiB
#ifndef __SVF_H__
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#define __SVF_H__
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/* CEM3320/Oberheim/Phrophet-style filter as described here: https://arxiv.org/pdf/2111.05592.pdf */
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#include <math.h>
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#include "util.h"
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class SVF12 {
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protected:
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float as1, as2;
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float kdiv;
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float kK, kQ;
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inline void updateCoeffs() {
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kdiv = 1 + kK/kQ + kK*kK;
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}
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public:
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typedef struct {
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float hp; // high-pass
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float bp; // band-pass
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float lp; // low-pass
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} Output;
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SVF12() {
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as1 = 0;
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as2 = 0;
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kK = tan(M_PI_4);
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kQ = M_SQRT1_2;
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updateCoeffs();
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}
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void setFrequency(float f) {
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kK = tan(M_PI_4 * clamp(f, 0, 1));
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updateCoeffs();
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}
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void setQ(float q) {
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kQ = q;
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updateCoeffs();
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}
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Output tick(float as) {
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Output out;
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out.hp = (as - (1/kQ + kK) * as1 - as2) / kdiv;
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float au = out.hp * kK;
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out.bp = au + as1;
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as1 = au + out.bp;
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au = out.bp * kK;
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out.lp = au + as2;
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as2 = au + out.lp;
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return out;
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}
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};
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// 12 and 24 dB/oct
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class SVF {
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public:
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enum Mode {
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MODE_HP_12,
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MODE_HP_24,
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MODE_BP_12,
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MODE_BP_24,
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MODE_LP_12,
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MODE_LP_24,
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};
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private:
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Mode mode;
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SVF12 first, second;
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public:
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SVF() {
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this->mode = MODE_LP_24;
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}
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void setMode(Mode mode) {
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this->mode = mode;
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}
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void setFrequency(float f) {
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first.setFrequency(f);
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second.setFrequency(f);
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}
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void setQ(float q) {
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first.setQ(q);
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second.setQ(q);
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}
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float tick(float as) {
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SVF12::Output in = first.tick(as);
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switch(mode) {
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case MODE_HP_12:
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return in.hp;
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case MODE_HP_24:
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return second.tick(in.hp).hp;
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case MODE_BP_12:
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return in.bp;
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case MODE_BP_24:
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return second.tick(in.bp).bp;
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case MODE_LP_12:
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return in.lp;
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case MODE_LP_24:
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return second.tick(in.lp).lp;
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}
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}
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};
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#endif |