public void updateFilter(LTISystem [] newFilter)
{
// prevent updating coefficients while we're in the middle of a filter operation. Prevents index out of bound exceptions
lock (filtLock)
{
bpFilter = newFilter;
}
}
public static LTISystem[] BandPass(double lofreq, double hifreq, int nSection)
{
if ((nSection % 2) == 1) nSection++; // force even # of sections
Complex[] pol = Poles(hifreq - lofreq, nSection);
LTISystem[] bpfilt = new LTISystem[nSection];
// translate the poles to band-pass position
Complex[] bpol = new Complex[nSection];
double wlo = 2 * Math.PI * lofreq;
double whi = 2 * Math.PI * hifreq;
double ang = Math.Cos((whi + wlo) / 2) / Math.Cos((whi - wlo) / 2);
for (int i = 0; i < nSection / 2; i++)
{
Complex p1 = new Complex(pol[i].Real + 1, pol[i].Imaginary);
Complex tmp = Complex.Sqrt(p1 * p1 * ang * ang * 0.25 - pol[i]);
bpol[2 * i] = (p1 * ang * 0.5) + tmp;
bpol[2 * i + 1] = (p1 * ang * 0.5) - tmp;
}
// convert each conjugate pole pair to
// difference equation
for (int i=0;i<nSection;i++) {
bpfilt[i] = new LTISystem(2,2);
// put in conjugate pole pair
bpfilt[i].b[1] = -2.0 * bpol[i].Real;
bpfilt[i].b[2] = bpol[i].Real * bpol[i].Real +
bpol[i].Imaginary * bpol[i].Imaginary;
// put zeros at (1,0) and (-1,0)
bpfilt[i].a[0] = 1.0;
bpfilt[i].a[1] = 0.0;
bpfilt[i].a[2] = -1.0;
// normalise to unity gain
double gain = (bpfilt[i].response((hifreq+lofreq)/2)).Magnitude;
bpfilt[i].a[0] = bpfilt[i].a[0]/gain;
// bpfilt[i].a[1] = bpfilt[i].a[1]/gain; // we know this is 0 since its a bandpass
bpfilt[i].a[2] = bpfilt[i].a[2]/gain;
}
return bpfilt;
}
private LTISystem notchPrototype(int harmonic)
{
LTISystem notch = new LTISystem(2, 2);
double BW = 2 * Math.PI * bandwidth / samplingFrequency;
double Wo = 2 * Math.PI * harmonic * notchFrequency / samplingFrequency;
double Gb = Math.Pow(10,-aPass / 20);
double beta = Math.Tan(BW/2)*Math.Sqrt(1 - Gb * Gb)/Gb;
double gain = 1 / (1 + beta);
notch.a[0] = gain;
notch.a[1] = -2 * gain*Math.Cos(Wo);
notch.a[2] = gain;
notch.b[1] = notch.a[1];
notch.b[2] = 2 * gain - 1;
return notch;
}
private LTISystem[] notchesPrototype()
{
LTISystem[] notchFilt = new LTISystem[numHarmonics];
for (int i = 0; i < numHarmonics; ++i)
{
notchFilt[i] = notchPrototype(i);
}
return notchFilt;
}
