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


//Low pass butterworth filter order=1 alpha1=0.1 
class FilterBuLp1
{
    const float cf[2] = {0.24523727525278560258, 0.50952544949442879485};
  public:
    FilterBuLp1()
    {}
    float step(float x) //class II 
    {
        v[0] = v[1];
        v[1] = x * cf[0]  + cf[1] * v[0];
        return (v[0] + v[1]);
    }
  private:
    float v[2]{};
};