Procedure TWOFFT(DATA1, DATA2:array of real;
                             var FFT1, FFT2:array of real; N:integer);
var
    C1R,C1I,C2R,C2I,CONJR,CONJI,H1R,H1I,H2R,H2I:real;  N2,J,J2:integer;
begin
    C1R:=0.5;
    C1I:=0;
    C2R:=0;
    C2I:=-0.5;
    For J:=1 To N do
    begin
        FFT1[2 * J - 1]:=DATA1[J];
        FFT1[2 * J]:=DATA2[J];
    end;
    FOUR1(FFT1, N, 1);
    FFT2[1]:=FFT1[2];
    FFT2[2]:=0;
    FFT1[2]:=0;
    N2:=2 * (N + 2);
    For J:=2 To ((N div 2) + 1) do
    begin
        J2:=2 * J;
        CONJR:=FFT1[N2 - J2 - 1];
        CONJI:=-FFT1[N2 - J2];
        H1R:=C1R * (FFT1[J2 - 1] + CONJR) - C1I * (FFT1[J2] + CONJI);
        H1I:=C1I * (FFT1[J2 - 1] + CONJR) + C1R * (FFT1[J2] + CONJI);
        H2R:=C2R * (FFT1[J2 - 1] - CONJR) - C2I * (FFT1[J2] - CONJI);
        H2I:=C2I * (FFT1[J2 - 1] - CONJR) + C2R * (FFT1[J2] - CONJI);
        FFT1[J2 - 1]:=H1R;
        FFT1[J2]:=H1I;
        FFT1[N2 - J2 - 1]:=H1R;
        FFT1[N2 - J2]:=-H1I;
        FFT2[J2 - 1]:=H2R;
        FFT2[J2]:=H2I;
        FFT2[N2 - J2 - 1]:=H2R;
        FFT2[N2 - J2]:=-H2I;
    end;
end;