The cyan plot is a spectrum of 50 Hz, and the magenta one is a 50.1 Hz sine wave (having amplitude 0.7). Both are sampled at 1024 samples/s. I performed a 1024 point FFT to get this spectrum.
Why is only the 50Hz spectrum a single value? Why does the 50.1 Hz sine consist of other frequencies apart from 50.1 Hz; where do these new frequencies come from?
I did not do any non-linear processing on the 50.1 Hz signal! Also the 50.1 Hz appears to have smaller maximum amplitude, i.e. it's not 0.7, when in fact the sine wave I generated has an amplitude of 0.7.
Why is this?
Obtained by MATALB command fft();