/// <summary>
/// Computes the IIR coefficients for a high-pass Butterworth filter.
/// </summary>
/// <param name="stopbandFreq">Stopband corner frequency (in Hz).</param>
/// <param name="passbandFreq">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.HighPass(double, double, double, double)"/>
public static (IEnumerable <double> numerator, IEnumerable <double> denominator) HighPass(double stopbandFreq, double passbandFreq, double passbandRipple, double stopbandAttenuation)
{
var(n, wc) = Designer.HighPass(stopbandFreq, passbandFreq, passbandRipple, stopbandAttenuation);
const double T = 2;
var(gain, zeros, poles) = TransferFunction(n);
wc = Helpers.MathFunctions.WarpFrequency(wc, T);
(gain, zeros, poles) = TransferFunctionTransformer.HighPass(gain, zeros, poles, wc);
return(Coefficients(gain, zeros, poles, T));
}
/// <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-pass Butterworth filter.
/// </summary>
/// <param name="lowStopbandFreq">Lower stopband corner frequency (in Hz).</param>
/// <param name="lowPassbandFreq">Lower passband corner frequency (in Hz).</param>
/// <param name="highPassbandFreq">Higher passband corner frequency (in Hz).</param>
/// <param name="highStopbandFreq">Higher stopband 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.BandPass(double, double, double, double, double, double)"/>
public static (double[] numerator, double[] denominator) BandPass(double lowStopbandFreq, double lowPassbandFreq, double highPassbandFreq, double highStopbandFreq, double passbandRipple, double stopbandAttenuation)
{
var(n, wc1, wc2) = Designer.BandPass(lowStopbandFreq, lowPassbandFreq, highPassbandFreq, highStopbandFreq, 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.BandPass(gain, zeros, poles, wc1, wc2);
return(Coefficients(gain, zeros, poles, T));
}
