character
chebyshev ripple	db (<0.0)
qfactor (resonator)	(>0.0)
frequency	Alpha Low Alpha Up or samplerate: Hz Lower corner Hz Midi note (69=A440) Upper corner Hz Midi note (69=A440)
more	matched z-transform (better off, check frequency response) prewarp (better on)
output	Signal bits (including sign): -1 bit saturation save brutal shift, this will remove shifts up to 4 positions by changing the factor, hence reducing accuracy by maximum 4 bits but more efficient calculation
execution


//Band pass butterworth filter order=4 alpha1=0.037453183520599 alpha2=0.063670411985019 
class FilterBuBp4
{
    const float cf[9] = {0.00003743561515783600, -0.64984203758803527062, 5.22187801143368535151, -18.62939109557171590836, 38.51794268736599491376, -50.46701448849155724474, 42.90303533134298419327, -23.11211667933892854876, 7.21544634991835387439};
  public:
    FilterBuBp4()
    {}
    float step(float x) //class II 
    {
        v[0] = v[1];
        v[1] = v[2];
        v[2] = v[3];
        v[3] = v[4];
        v[4] = v[5];
        v[5] = v[6];
        v[6] = v[7];
        v[7] = v[8];
        v[8] = x * cf[0]  + cf[1] * v[0] + cf[2] * v[1] + cf[3] * v[2] + cf[4] * v[3] + cf[5] * v[4] + cf[6] * v[5] + cf[7] * v[6] + cf[8] * v[7];
        return (v[0] + v[8])- 4 * (v[2] + v[6]) + 6 * v[4];
    }
  private:
    float v[9]{};
};