SignalUtils.IirInitBQ Method

procedure IirInitBQ(const sos: TVec; var IIRState: TIirState; ComplexData: Boolean);

Initialize an IIR filter with second order sections.

#	Name	Type
1	sos	TVec
2	IIRState	TIirState
3	ComplexData	Boolean

Result: stored in self (calling object)

Remarks:

Initialize an IIR filter by initializing the IirState variable. Set ComplexData to True, if the data stream to be filtered will be complex. The Sos (real) vector variable contains second order sections as produced by the ZeroPoleToSOS function:

(B00, B10, B20, A00, A10, A20), (B01, B11, B21, A01, A11, A21), (.... ),...

B - numerator sections array A - denumarator sections array

Using second order sections to compute an IIR filter results in higher numerical accuracy and greater filter stability at a slightly higher cost on performance.

Examples

uses MtxExpr, Math387, MtxVec, SignalUtils, MtxVecTee, MtxVecEdit, IIRFilters;

procedure TForm42.Button1Click(Sender: TObject);
var b,c,Response,Response1,sos: Vector;
State: TIirState;
n,i: integer;
begin
    Tone(b,300,6/300,0,1);

    //   Alternative: try gaussian noise
    //    b := RandGauss(300);

    c.Size(b);
    ChebyshevIFilter(6,0.2,[0.6],ftLowpass,false,sos); //design filter
    FillChar(State,SizeOf(State),0);
    IirInitBQ(sos,State);  //initialize filtering structure
    try
        c.Copy(b); //make backup of data
        IirFilter(c,State); //apply filter to data

        DrawIt([b,c],['Original signal','Filtered signal']);
        FrequencyResponse(b,nil,Response,8,True,wtHanning);
        FrequencyResponse(c,nil,Response1,8,True,wtHanning);
        DrawIt([Response,Response1],['Orig. signal','Filtered']);
    finally
        IirFree(State);
    end;
end;