EarFilter.h

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#pragma once
 
namespace krotos
{
    //==============================================================================
    class EarFilter
    {
      public:
        EarFilter();
 
        void configure(float sampleRate);
 
        std::vector<float> processSignal(std::vector<float>& inputSignal);
 
      private:
        std::vector<float> getLowPassFilterCoefficients(float normalizedFrequency, float qualityFactor);
 
        std::vector<float> convertToHighPass(const std::vector<float>& lowPassCoefficients);
 
        void applyIIRFilter(const std::vector<float>& inputSignal, dsp::IIR::Filter<float>& filter,
                            std::vector<float>& filteredSignal);
 
        void applyFIRFilter(const std::vector<float>& inputSignal, const std::vector<float>& coefficients,
                            std::vector<float>& filteredSignal);
 
        void calculateTransferFunction(const std::vector<float> b, const std::vector<float> a, int numPoints);
 
        std::vector<float> elementWiseDivision(const std::vector<float>& vector1, const std::vector<float>& vector2);
 
        std::vector<float> fir2(int N, std::vector<float>& freqResponse, const std::vector<float>& gain);
 
        std::vector<float> linspace(float start, float end, int numPoints)
        {
            std::vector<float> result(numPoints);
            float step = (end - start) / (numPoints - 1);
 
            for (int i = 0; i < numPoints; ++i)
            {
                result[i] = start + i * step;
            }
 
            return result;
        }
 
        float m_sampleRate{-1.0f};
 
        const float m_maxFreq{20000.0f};
 
        // hopSize in seconds
        float m_hopSizeSec = 0.0058f;
        float m_hopSizeSamples;
 
        // second order IIR high pass parameters
        // Hz - corner frequency
        float m_fc = 680.0f;
        // quality factor
        float m_q = 0.65f;
        std::vector<float> m_magResponse;
        std::vector<float> m_normalisedFreqs;
        std::vector<float> m_freqResponse;
        // IIR coeff vectors
        std::vector<float> m_a;
        std::vector<float> m_b;
        dsp::IIR::Filter<float> m_filter;
        std::vector<float> m_gain;
 
        // FIR filter parameters
        // order
        int N = 50;
        std::vector<float> m_firCoeffb;
        // Killian dataset
        std::vector<float> m_freqs = {0.0f,
                                      100.0f, // Freq at Hz
                                      150.0f,  200.0f,  300.0f,  400.0f,  500.0f,  700.0f,   1000.0f,
                                      1500.0f, 2000.0f, 2500.0f, 3000.0f, 3500.0f, 4000.0f,  4500.0f,
                                      5000.0f, 6000.0f, 7000.0f, 8000.0f, 9000.0f, 10000.0f, 20000.0f};
 
        // Killian dataset - minimum audible field gains (linear)
        std::vector<float> m_gains = {std::numeric_limits<float>::epsilon(),
                                      0.0363078054770101f,
                                      0.102329299228075f,
                                      0.192752491319094f,
                                      0.407380277804113f,
                                      0.645654229034656f,
                                      0.812830516164099f,
                                      0.944060876285923f,
                                      1.0f,
                                      1.14815362149688f,
                                      1.44543977074593f,
                                      1.86208713666287f,
                                      2.26464430759306f,
                                      2.54097270554930f,
                                      2.54097270554930f,
                                      2.29086765276777f,
                                      1.81970085860998f,
                                      0.954992586021436f,
                                      0.462381021399260f,
                                      0.278612116862977f,
                                      0.229086765276777f,
                                      0.245470891568503f,
                                      0.245470891568503f};
    };
} // namespace krotos