MoogVcf.h

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namespace krotos
{
    //==============================================================================
    class MoogVcf
    {
      public:
        //--------------------------------------------------------------------------
 
        void setUpFirst(double sampleRate, int /*samplesPerBlock*/)
        {
            m_sr = static_cast<float>(sampleRate);
            k = 1.0f / m_sr;
        }
 
        //--------------------------------------------------------------------------
 
        float getSr() { return m_sr; }
 
        //--------------------------------------------------------------------------
 
        void updateCutoff(float _f0)
        {
            // Calculate state variables from former parameter values
            A0P = 1.0f + (om0 * k) / 2.0f;
            A0M = 1.0f - (om0 * k) / 2.0f;
            A1 = (om0 * k) / 2.0f;
            A3 = 2.0f * r * om0 * k;
 
            // Calculate state variables from new parameter values
            om0New = tau * _f0;
            A0PNew = 1.0f + (om0New * k) / 2.0f;
            A1New = (om0New * k) / 2.0f;
 
            // If resonance is not readjusted just update the A3New filter coefficient
            A3New = 2.0f * r * om0New * k;
        }
 
        //--------------------------------------------------------------------------
 
        void updateResonance(float _r)
        {
            // Calculate state variables from former parameter values
            A3 = 2.0f * r * om0 * k;
 
            // Calculate state variables from new parameter values
            rNew = _r;
 
            A3New = 2.0f * rNew * om0 * k;
        }
 
        //--------------------------------------------------------------------------
 
        float process(float inputSampleNow, float inputSampleBefore)
        {
            float xf1[4];
            // Update the state xf1 = xf;
            std::memcpy(xf1, xf, sizeof(float) * 4);
 
            xf[0] = (-A3New * xf[3] + A0M * xf1[0] - A3 * xf1[3] +
                     om0 * k / 2.0f * (inputSampleNow + inputSampleBefore)) /
                    A0PNew;
            xf[1] = (A1New * xf[0] + A1 * xf1[0] + A0M * xf1[1]) / A0PNew;
            xf[2] = (A1New * xf[1] + A1 * xf1[1] + A0M * xf1[2]) / A0PNew;
            xf[3] = (A1New * xf[2] + A1 * xf1[2] + A0M * xf1[3]) / A0PNew;
 
            // Update parameters
            om0 = om0New;
            r = rNew;
            // Return the output
            return xf[3];
        }
 
      private:
        static constexpr float tau = 2.0f * 3.1415926535f;
        const float initialF = 20.0f;
        // Main Parameters
        float m_sr;
        float om0 = tau * initialF;
        float om0New;
        float r = 0.0f;
        float rNew;
        // Derived Parameters
        float k;
 
        // State variables and coefficients
        float A0P;
        float A0PNew;
        float A0M;
        float A1;
        float A1New;
        float A3;
        float A3New;
        float xf[4] = {0.0};
    };
} // namespace krotos