/// <summary>
/// Creates an IIR filter from zeros and poles. The zeros and poles must be made up of real and complex conjugate pairs.
/// </summary>
public IirFilter(ZeroPoleGain zeroPoleGain)
{
Debug.Assert(zeroPoleGain.Zeros.Length == zeroPoleGain.Poles.Length);
this.zeroPoleGain = zeroPoleGain;
transferFunction = FilterModifiers.ConvertSosToTransferFunction(sosGain);
sosGain = FilterModifiers.ConvertZeroPoleToSosFilter(zeroPoleGain);
this.sections = new FilterChain(sosGain.Sections);
this.order = sosGain.Sections.Sum(x => x.Order);
//Check whether this is linear phase
double[] b = transferFunction.B;
isLinearPhase = true;
for (int i = 0; i < b.Length; i++)
{
if (b[i] != b[b.Length - 1 - i] && b[i] != -b[b.Length - 1 - i])
{
isLinearPhase = false;
break;
}
}
return;
}
public static ZeroPoleGain ConvertSosToZeroPole(SosGain sosGain)
{
double gain = sosGain.Gain;
Complex[] zeros = sosGain.Sections.SelectMany(x => x.ZeroPoleGain.Zeros).ToArray();
Complex[] poles = sosGain.Sections.SelectMany(x => x.ZeroPoleGain.Poles).ToArray();
return new ZeroPoleGain(gain, zeros, poles);
}
// Calculate transfer function polynomials of the sections together (similiar to sos2tf in matlab)
public static TransferFunction ConvertSosToTransferFunction(SosGain sosGain)
{
double[] coefA = sosGain.Sections.Select(x => x.TransferFunction.A).Aggregate(new[] { 1.0 }, (x, y) => Helpers.Convolution(x, y));
double[] coefB = sosGain.Sections.Select(x => x.TransferFunction.B).Aggregate(new[] { 1.0 }, (x, y) => Helpers.Convolution(x, y));
// Incorporate gain into transfer function
coefB = Array.ConvertAll(coefB, x => sosGain.Gain * x);
// Remove trailing zeros
if (coefA.Length > 3 && coefA.Last() == 0)
Array.Resize(ref coefA, coefA.Length - 1);
if (coefB.Length > 3 && coefB.Last() == 0)
Array.Resize(ref coefB, coefB.Length - 1);
return new TransferFunction(coefB, coefA);
}
