function [f,TXF]=VTB7_2(x,f,dt,n)

%VTB7_2 
%  [W,TF] = VTB7_2(x,f,dt,n)
%  generates frequency response function (H(iw))
%  dt is the time step of the sampled data
%  n is the number of points in the fft.
%  recommended value is 256 unless zooming
%  use higher n for zooming.  Load the data
%  in VTB7_2ex.mat for example.

lf = length(f);

if (nargin == 3), n=256; end

if n < 128

  n=256;

end

w=hanning(lf);

x=x(:);

f=f(:);

xw=x.*w;

fw=f.*w;

FX=fft(xw);

FF=fft(fw);

SXF=FF.*conj(FX);

SXX=FX.*conj(FX);

SFF=FF.*conj(FF);

SFX=FX.*conj(FF);

TXF=SXX./SXF;TXF2=SFX./SFF;

lTXF2=length(TXF)/2;

freq=[0 ((1:lTXF2-1)/lTXF2/2/dt)]';

TXF=TXF(1:lTXF2);

mag=abs(TXF);

ang=angle(TXF)*180/pi;

semilogy(freq,mag)

title('Txf - Transfer function magnitude'), ...

xlabel('Frequency (Hz)'), grid

text(0,0,'Press Return To Continue','sc')

pause

plot(freq,ang)

title('Txf - Phase'), ...

xlabel('Frequency (Hz)'), grid

text(0,0,'Press Return To Continue','sc')

pause

Coh=(abs(SXF).^2)./SXX./SFF;

plot(freq,Coh(1:lTXF2))

title('Txf - Coherence'), ...

xlabel('Frequency (Hz)'), grid

text(0,0,'Press Return To Continue','sc')

pause