Howtosignalprocessing
- Why do we shift zero-frequency component to center of spectrum?
- Why is FFT shift used?
- How does FFT shift work?
- Do I need to use Fftshift?
Why do we shift zero-frequency component to center of spectrum?
The zero-frequency is shifted to the center in both audio and image spectrums, simply because this is how people normally expect to see a spectrum. I.e. it is per convention. The spectrum content is not changed in any way, and everything you can derive after the shift, you can derive before the shift.
Why is FFT shift used?
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.
How does FFT shift work?
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.
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.
