Formant filter

gistfile1.cpp

double maxiFilter::formant(double input, double centerFreq, double q, double gain) {
    cutoff = centerFreq;
    
    //offset gain
    gain += 1;
    //gain *= 4;
    //calculate poles and coeffs
    w0 = TWOPI * cutoff / 44100;
    alpha = sin(w0)/(20*q);
    b0 =   alpha*gain;
    b1 =   0;
    b2 =  -alpha*gain;
    a0 =   1 + alpha/gain;
    a1 =  -2*cos(w0);
    a2 =   1 - alpha/gain;
    
    //apply filter
    output = (b0/a0)*input + (b1/a0)*in1 + (b2/a0)*in2 - (a1/a0)*out1 - (a2/a0)*out2;
    
    //update memory
    out2 = out1;
    out1 = output;
    in2 = in1;
    in1 = input;
    
    return output;
}