1) How many stages are in N numbers for a FFT? I know N=8 has 3 stages and N=4 has 2 stages ? 2) The DFT formula converts a signal from the time domain in to the frequency domain. Is this done by comparing x[n] against signals known as sinusoidal basis functions? are e-j2 pi kn/N sinusoidal basis functions ? I know it uses Correlation and that mean it compares the variables together but I am not 100% sure how this work ? 3) In a butterfly diagram the bottom line is alway -1, but why? PS, I have been reading and watch videos on the DFT and the FFT and I have learned a lot, but I am just not sure about this questions.