DFT analysis of a physical signal what is the reason for the result that has been obtained from the DFT of the signal of these two images. The first image is a DFT analysis of a physical signal u which has a time history shown below sampled at a 1000Hz the second image is the square of the signal u which has a time history shown in the image after the time history of u
The first DFT plot represents a typical case of Gibbs phenomenon.