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IIRFilters.BesselFilter Function
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The resulting transfer function is returned in the state-space form with A,B,C,D variables.

Pascal
function BesselFilter(Order: integer; const CutoffFreq: array of double; FilterType: TFilterType; Analog: boolean; const A: TMtx; const B: TVec; const C: TVec; out d: double): double; overload;
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Example

Design a fifth order analog lowpass filter with the cutoff frequency at 3 rad/sec.  

Note: This example does not actually filter data. It only designs the filter. To see how to actually apply the filter check the IirInit and IirInitBQ routines. 

 

  uses MtxExpr, Math387, MtxVec, SignalUtils, MtxVecTee, MtxVecEdit, IirFilters,
       LinearSystems;

  procedure TForm1.Button1Click(Sender: TObject);
  var z,p, num,den, FreqFr,Response: Vector;
      Order: integer;
      k,Bw,Wc: double;
      WcArray: TDoubleArray; //modified 3dB frequency
  begin
      BesselFilter(5,[3],ftLowpass,True,num,den);
      FreqFr.Length := 1000;         //Define the frequency grid (logarithmic)
      LogRamp(FreqFr,-1,1); //between 0.1 (=10^(-1)) and 10 (=10^1) rad/sec
      FrequencyResponseS(num,den,FreqFr,Response); //Laplace
      DrawIt(FreqFr,20*Log10(Abs(Response)));  //logarithmic frequency and amplitude
  end;

 

  #include "MtxExpr.hpp"
  #include "MtxVecEdit.hpp"
  #include "MtxVecTee.hpp"
  #include "SignalUtils.hpp"
  #include "IirFilters.hpp"
  #include "LinearSystems.hpp"

  void __fastcall TForm1::BitBtn1Click(TObject *Sender)
  {
    sVector num, den, FreqFr, Response;

    BesselFilter(5,OPENARRAY(double,(3)),ftLowpass,true,num,den);
    FreqFr.Length = 1000;         //Define the frequency grid (logarithmic)
    LogRamp(FreqFr,-1,1); //between 0.1 (=10^(-1)) and 10 (=10^1) rad/sec
    FrequencyResponseS(num,den,FreqFr,Response); //Laplace
    DrawIt(FreqFr,20*Log10(Abs(Response)),"Frequency response",false);  //logarithmic frequency and amplitude
  }
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