Hello, I have a simple cosine f = 50Hz. When I generate Matlab code to produce 1/2 second of this signal and take the FFT, the response correctly shows a spike at 50 Hz. However, when I bracket the signal with 1/2 seconds of zeros on either side, the frequency response is showing a spike at 75 Hz. Does anyone know why this might occur, and how might one rectify it? Thanks so much!