Fftshift vs fft

1. What is FFT and Fftshift?
2. When should I use Fftshift?
3. Do I need to use Fftshift?
4. What does the Fftshift function do?

What is FFT and Fftshift?

fft computes the discrete Fourier transform and by definition the output is complex. fftshift doesn't compute anything except swaping the position of the samples, so if your input is real, you get real output.

When should I use Fftshift?

It is useful for visualizing a Fourier transform with the zero-frequency component in the middle of the spectrum. For vectors, fftshift(X) swaps the left and right halves of X . For matrices, fftshift(X) swaps quadrants one and three of X with quadrants two and four.

Do I need to use Fftshift?

It depends on what you are going to do with the transformed data. If you don't perform an fftshift before transforming, the fft result will have every other value multiplied by -1. This doesn't matter if you plan to view the magnitude or magnitude squared of the result.

What does the Fftshift function do?

Y = fftshift( X ) rearranges a Fourier transform X by shifting the zero-frequency component to the center of the array. If X is a vector, then fftshift swaps the left and right halves of X . If X is a matrix, then fftshift swaps the first quadrant of X with the third, and the second quadrant with the fourth.