Why i can't plot a spectrum of a rectangular window function?
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Hi everyone! I have a problem, so could you explain to me? I knew that, to plot a spectrum of any windows function we can use "wvtool" command in Matlab or you can find a code to do this on google. But, why i can do this with my code? My plot (use my code) is different with that uses "wvtool". P/s:i understood that spectrum of any window (rect, hanning....) function is FFT of the windows. Is that right or wrong?. And my code:
rect=rectwin(N+1); % create a rectangular windows function
taxis=-N/2:N/2; % time axis
plot(taxis,rect); % Plot rectangular windows in time domain.
fftrect=fft(rect); % calculate spectrum of the rectangular window
plot(taxis,20*log10(abs(fftrect))) % Plot rectangular windows in frequency domain.
wvtool(rect) % Plot rectangular windows in frequency domain use "wvtool" to compare
Greg Dionne on 29 Jan 2018
If you line up the frequency points, you'll see that your FFT is showing the zeros only. If you crank up the number of points in the FFT you are computing you'll see a similar picture:
More Answers (1)
Honglei Chen on 29 Jan 2018
There is a mistake in your plotting command. Because the spectrum is in frequency domain, you need to have a frequency axis instead of time axis.
As to the curve it self, your concept is correct. However, the one in wvtool is computed with 1024 points, you can reproduce it using the following code snippet.
nfft = 1024;
fftrect=fft(rect,nfft); % calculate spectrum of the rectangular window
faxis = 0:2/nfft:2-2/nfft;
plot(faxis(1:nfft/2),20*log10(abs(fftrect(1:nfft/2)))) % Plot rectangular windows in frequency domain.