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Why should I use 2 fftshift?

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moose
moose 2015-7-31
评论： moose 2015-8-1
Hello if I have signal x (in time domain).
I saw that sometimes people do fftshift(fft(ffshift(x))). Now, I understand the usage of fftshift to move the DC to the center. But what's the reasoning behind using fftshift twice?
Seems to me that fftshift(fft(x)), should be enough.
Am I missing something here?
Thanks

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回答（1 个）

Walter Roberson
Walter Roberson 2015-7-31
You can test it yourself to see if the two are equal.
The magnitudes of the two are equal, but the real and imaginary components are different.
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moose
moose 2015-8-1
thank you.
yes, I saw that the subtraction gives me zero.
so, what's the difference? or, what's the more right way to do it?
I can understand my way fftshift(fft(x)). you're shifting the resulting fft signal.
But, what does it mean, fftshift(fft(fftshift(x)))? it seems that you're first doing the shift on x which is in time domain???

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