Why do I have "inside" oscillations when I take the fft of my data

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Hugo 2025-6-24

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https://ww2.mathworks.cn/matlabcentral/answers/2178005-why-do-i-have-inside-oscillations-when-i-take-the-fft-of-my-data

评论： Mathieu NOE 2025-6-24

Hi,

I have a data sample that I need to take into the frequency domain, unfortunately I get these oscillations in between the actual negatives and positive values of what I expect, on the left is the sampled signal and on the right the real and imaginary part of its fft.

imag(fftshift(fft(sample)))
real(fftshift(fft(sample)))

Yet what I expect should look like this,

Where did I go wrong about the fft?

Thank you.

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Hugo 2025-6-24

Well , that was another issue linked to the fact that I plotted using the angular frequency instead of the frequency. Here is what I get now with all issues solved.