How to implement rectangular and welch window in MATLAB to plot fft respectively?

Hello Everybody,

I just want to know that how to implement rectangular and welch window in MATLAB to plot fft? And i want to know that what will be the effect if i do not use these in our fft? I have written the following code so please suggest how to specify rectangular and welch window in this code.

I = load('data1.asc');

for i = 1:2048

x = I(:,2);

end

Fs = 40;

t = 0:1/Fs:(2e3*1/Fs)-1/Fs;

T = 1/Fs;

L = 2048;

NFFT = 2^nextpow2(L);

Y = abs(fft(x,NFFT))/L;

f = Fs/2*linspace(0,1,NFFT/2+1);

plot(f,2*abs(Y(1:NFFT/2+1)))

axis([0 50 0 40])

Answer 1

[Honglei Chen]

Rectangular window is the same as no window. For Welch window, you can find it on file exchange at

http://www.mathworks.com/matlabcentral/fileexchange/38978-welchwin-welch-parabolic-window-function

(Disclaimer: I haven't personally used it so I cannot comment on its quality)

If you have a window, w, you just need to do the following in your code instead:

Y = abs(fft(x.*w,NFFT))/L;

Answer 2

[Deyan Dobromirov]

The implementation fails to create zeros at both ends. Here is my version:

function w = welchwin(n)
  m = floor(n/2); k = (0:m-1)';
  w = 1 - (2*k/n - 1).^2;
  if(mod(n, 2) ~= 0), w = [w; 1]; end
  w = [w; flipud(w(1:m, 1))];
end