For an experiment i have a simple application that takes a quadrature signal from a radio and then does the following: Complex FFT -> Inverse FFT -> Cartesian to Polar -> audio out If I tune the radio to an AM signal I can demodulate it perfectly well by this but it depends on how the FFT is processed. In the FFT routine, I apply a window and if it is anything other than a rectangular window the sound is distorted even to the point where it's only noise. The sample thing if there is any FFT sample overlap. Why is this the case? As I mentioned this is an experiment. I already have a fully functional spectrum scope which provides very good resolution using a Blackman window and sample overlap. I wish to add demodulation of the signals in the frequency domain starting from the spectrum but this is problematic. Thanks for any insight (I'm a beginner in DSP).