/// <summary>
/// Computes the IIR coefficients for a notch Butterworth filter.
/// </summary>
/// <param name="centralFreq">Filter central frequency.</param>
/// <param name="Q">Quality factor.</param>
/// <param name="passbandRipple">Maximum allowed passband ripple.</param>
/// <param name="stopbandAttenuation">Minimum required stopband attenuation.</param>
/// <returns>IIR coefficients.</returns>
/// <seealso cref="Designer.Notch(double, double, double, double)"/>
public static (IEnumerable <double> numerator, IEnumerable <double> denominator) Notch(double centralFreq, double Q, double passbandRipple, double stopbandAttenuation)
{
var(n, wc1, wc2) = Designer.Notch(centralFreq, Q, passbandRipple, stopbandAttenuation);
const double T = 2;
var(gain, zeros, poles) = TransferFunction(n);
wc1 = Helpers.MathFunctions.WarpFrequency(wc1, T);
wc1 = Helpers.MathFunctions.WarpFrequency(wc2, T);
(gain, zeros, poles) = TransferFunctionTransformer.BandStop(gain, zeros, poles, wc1, wc2);
return(Coefficients(gain, zeros, poles, T));
}
/// <summary>
/// Computes the IIR coefficients for a band-stop Butterworth filter.
/// </summary>
/// <param name="lowPassbandFreq">Lower passband corner frequency (in Hz).</param>
/// <param name="lowStopbandFreq">Lower stopband corner frequency (in Hz).</param>
/// <param name="highStopbandFreq">Higher stopband corner frequency (in Hz).</param>
/// <param name="highPassbandFreq">Higher passband corner frequency (in Hz).</param>
/// <param name="passbandRipple">Maximum allowed passband ripple.</param>
/// <param name="stopbandAttenuation">Minimum required stopband attenuation.</param>
/// <returns>IIR coefficients.</returns>
/// <seealso cref="Designer.BandStop(double, double, double, double, double, double)"/>
public static (double[] numerator, double[] denominator) BandStop(double lowPassbandFreq, double lowStopbandFreq, double highStopbandFreq, double highPassbandFreq, double passbandRipple, double stopbandAttenuation)
{
var(n, wc1, wc2) = Designer.BandStop(lowPassbandFreq, lowStopbandFreq, highStopbandFreq, highPassbandFreq, passbandRipple, stopbandAttenuation);
const double T = 2;
var(gain, zeros, poles) = TransferFunction(n);
wc1 = Helpers.MathFunctions.WarpFrequency(wc1, T);
wc2 = Helpers.MathFunctions.WarpFrequency(wc2, T);
(gain, zeros, poles) = TransferFunctionTransformer.BandStop(gain, zeros, poles, wc1, wc2);
return(Coefficients(gain, zeros, poles, T));
}