SoundMatrixDecoder.h

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#pragma once
 
#include <cstdint>
#include <cmath>
#include <array>
#include <vector>
#include <tuple>
 
#ifndef M_PI
#define M_PI 3.14159265358979323846
#endif
 
namespace Ship {
 
class SoundMatrixDecoder {
  public:
    SoundMatrixDecoder(int32_t sampleRate);
    ~SoundMatrixDecoder() = default;
 
    void ResetState();
 
    std::tuple<const uint8_t*, int> Process(const uint8_t* buf, size_t len);
 
  private:
    struct BiquadCascade {
        double X[4] = {}; // Input history
        double Y[4] = {}; // Output history
    };
 
    struct FilterCoefficients {
        double A[5]; // Feedforward (numerator)
        double B[4]; // Feedback (denominator, excluding b0=1)
    };
 
    struct AllPassChain {
        double Freq = 0;
        double FreqMin = 0;
        double FreqMax = 0;
        double SweepRate = 0;
        double XHist[4] = {};
        double YHist[4] = {};
        bool Ready = false;
    };
 
    static constexpr int gMaxDelay = 1024;
    struct CircularDelay {
        std::array<float, gMaxDelay> Data = {};
        int Head = 0;
        int Length = 0;
    };
 
    FilterCoefficients DesignLowPass(double frequency, int32_t sampleRate);
 
    FilterCoefficients DesignHighPass(double frequency, int32_t sampleRate);
 
    float ProcessFilter(float sample, BiquadCascade& state, const FilterCoefficients& coef);
 
    void PrepareAllPass(AllPassChain& chain, int32_t sampleRate);
 
    float ProcessAllPass(float sample, AllPassChain& chain, bool negate);
 
    float ProcessDelay(float sample, CircularDelay& buffer);
 
    static int16_t Saturate(float value);
 
    int32_t mDelayLength = 0;
    double mAllPassBaseRate = 1.0; // Precomputed for ProcessAllPass
 
    // Filter coefficients (computed once per sample rate)
    FilterCoefficients mCoefCenterHP;
    FilterCoefficients mCoefCenterLP;
    FilterCoefficients mCoefSurroundHP;
    FilterCoefficients mCoefSubLP;
 
    // Per-channel filter states
    BiquadCascade mCenterHighPass;
    BiquadCascade mCenterLowPass;
    BiquadCascade mSurrLeftMainHP;
    BiquadCascade mSurrLeftCrossHP;
    BiquadCascade mSurrRightMainHP;
    BiquadCascade mSurrRightCrossHP;
    BiquadCascade mSubLowPass;
 
    // Phase processing
    AllPassChain mPhaseLeftMain;
    AllPassChain mPhaseLeftCross;
    AllPassChain mPhaseRightMain;
    AllPassChain mPhaseRightCross;
 
    // Timing
    CircularDelay mDelaySurrLeft;
    CircularDelay mDelaySurrRight;
 
    // Output buffer
    std::vector<int16_t> mSurroundBuffer;
};
 
} // namespace Ship