init

Source/DSP/BiquadFilters.h

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+#pragma once
+#include "DSPConstants.h"
+#include "../AlgorithmPresets.h"
+#include <array>
+
+namespace FDNReverb {
+     // -----------------------------------------------------------------------------
+     // Biquad helpers (Direct Form II Transposed - most robust)
+     // -----------------------------------------------------------------------------
+    struct BiquadCoeffs {
+        float b0{ 1.f }, b1{ 0.f }, b2{ 0.f };
+        float            a1{ 0.f }, a2{ 0.f };
+    };
+
+    struct BiquadState {
+        float s1{ 0.f }, s2{ 0.f };
+        inline float tick(float x, const BiquadCoeffs& c) noexcept {
+            float y = c.b0 * x + s1;
+            s1 = c.b1 * x - c.a1 * y + s2;
+            s2 = c.b2 * x - c.a2 * y;
+            return y;
+        }
+        void reset() noexcept { s1 = s2 = 0.f; }
+    };
+
+     // -----------------------------------------------------------------------------
+    //  Filter design utilities
+     // -----------------------------------------------------------------------------
+    namespace FilterDesign {
+        BiquadCoeffs lowShelf(float fcHz, float gainDB, double sampleRate);
+        BiquadCoeffs highShelf(float fcHz, float gainDB, double sampleRate);
+        BiquadCoeffs peak(float fcHz, float gainDB, float Q, double sampleRate);
+        BiquadCoeffs highPass1st(float fcHz, double sampleRate);
+        BiquadCoeffs allpass1st(float fcHz, double sampleRate);
+
+        // Design absorption filter cascade for delay lines
+         // : function internal MagnitudeResponseFitter
+        std::array<BiquadCoeffs, ABSO_STAGES> designAbsorption(
+            int delaySamples, double sampleRate,
+            const std::array<float, NUM_BANDS>& rt60,
+            float hfDamping, float lfAbsorption);
+    }
+} // namespace FDNReverb