init

Source/DSP/Filter.h

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+#pragma once
+#include <cmath>
+#include <algorithm>
+
+enum class FilterType { LowPass12 = 0, LowPass24, BandPass, HighPass, Notch, NumTypes };
+
+class Filter {
+public:
+    void prepare(double sr) {
+        sampleRate = sr;
+        reset();
+    }
+
+    void reset() {
+        for (int i = 0; i < 4; ++i) {
+            stage[i] = 0.0f;
+        }
+    }
+
+    void setCoefficients(float cutoff, float res, FilterType type) {
+        cutoff = std::clamp(cutoff, 20.0f, static_cast<float>(sampleRate * 0.49));
+        resonance = std::clamp(res, 0.0f, 1.0f);
+        filterType = type;
+
+        float g = std::tan(static_cast<float>(pi) * cutoff / static_cast<float>(sampleRate));
+        float k = 2.0f - 2.0f * resonance;
+        float a1 = 1.0f / (1.0f + g * (g + k));
+        float a2 = g * a1;
+
+        gCoeff = g;
+        kCoeff = k;
+
+        m0 = 0.0f;
+        m1 = 0.0f;
+        m2 = 0.0f;
+        m3 = 0.0f;
+
+        switch (filterType) {
+            case FilterType::LowPass12:
+                m0 = 0.0f; m1 = 0.0f; m2 = a2; m3 = 0.0f;
+                break;
+            case FilterType::LowPass24:
+                m0 = 0.0f; m1 = 0.0f; m2 = 0.0f; m3 = a2 * a2;
+                break;
+            case FilterType::BandPass:
+                m0 = 0.0f; m1 = a2; m2 = 0.0f; m3 = 0.0f;
+                break;
+            case FilterType::HighPass:
+                m0 = 1.0f; m1 = -a1; m2 = -a2; m3 = 0.0f;
+                break;
+            case FilterType::Notch:
+                m0 = 1.0f; m1 = -a1 * k; m2 = -a2; m3 = 0.0f;
+                break;
+            case FilterType::NumTypes:
+                break;
+        }
+    }
+
+    float process(float input) {
+        float denom = 1.0f + kCoeff * gCoeff + gCoeff * gCoeff;
+        float hp = (input - (kCoeff + gCoeff) * stage[0] - stage[1]) / denom;
+        float bp = gCoeff * hp + stage[0];
+        float lp = gCoeff * bp + stage[1];
+
+        stage[0] = gCoeff * hp + bp;
+        stage[1] = gCoeff * bp + lp;
+
+        float hp2 = (lp - (kCoeff + gCoeff) * stage[2] - stage[3]) / denom;
+        float bp2 = gCoeff * hp2 + stage[2];
+        float lp2 = gCoeff * bp2 + stage[3];
+
+        stage[2] = gCoeff * hp2 + bp2;
+        stage[3] = gCoeff * bp2 + lp2;
+
+        float output = 0.0f;
+
+        switch (filterType) {
+            case FilterType::LowPass12:
+                output = lp;
+                break;
+            case FilterType::LowPass24:
+                output = lp2;
+                break;
+            case FilterType::BandPass:
+                output = bp;
+                break;
+            case FilterType::HighPass:
+                output = hp;
+                break;
+            case FilterType::Notch:
+                output = input - bp;
+                break;
+            case FilterType::NumTypes:
+                output = input;
+                break;
+        }
+
+        return output;
+    }
+
+private:
+    static constexpr float pi = 3.14159265358979323846f;
+    double sampleRate = 44100.0;
+    float stage[4] = {0.0f, 0.0f, 0.0f, 0.0f};
+
+    float gCoeff = 0.0f, kCoeff = 0.0f;
+    float m0 = 0.0f, m1 = 0.0f, m2 = 0.0f, m3 = 0.0f;
+    float resonance = 0.0f;
+    FilterType filterType = FilterType::LowPass12;
+};