FFT on a stored waveform

2012 2 19
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更新时间：2013 10 20
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Hi everybody,
I have a time domain semi sinusoidal waveform stored in excell file in numerical format. Coul you please tell me how can I do FFT on that?
Regards,

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Image Analyst
Image Analyst 2012-2-19

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The xlsread() and fft() functions immediately spring to mind. Did you try them?

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Alzapoa
Alzapoa 2012-2-19
Thands a lot. they work, but the fft() just do a numerical calculation could you tell me how to plot the elements. I tried the plot() command but it's just look like a line not a spectrum.
regards,
Wayne King
Wayne King 2012-2-20
If xdft is the output of fft, then plot(abs(xdft)). The reason that plot(xdft) doesn't look right is because the output of fft() is in general complex-valued (as it should be).
Image Analyst
Image Analyst 2012-2-22
If the plot of the spectrum doesn't look like a line plot, what's it supposed to look like? You can use bar() if you want - would that be better? Of course you have to take either the real, imaginary, or magnitude like Wayne said. You might also want to plot the log of the amplitude if your signal looks just like one giant sharp spike, like it should for a mostly sinusoidal signal.

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