I am carrying out FFT analysis to compare two waves. One looks very much like a sine wave the other has an extra dip occuring at half the frequency of the main wave. I have been thinking around how I might expect this to show up in the FFT analysis. At first i was expecting to see a smaller peak at half the main frequency but after a while I thought that it may just result in a few more higher harmonics due to the fact that the wave is becoming more complex. I did the FFT and I didnt see a peak at half frequency. so I guess the second conclusion is correct btu I still cant reconcile why I would expect to see a peak at half frequency of the main peak?