Hello all. I have two functions in time[tex] f_1(t) [/tex] and [tex] f_2(t) [/tex] composed of the same set of frequencies such that, say, [tex] f_1(t) = \sum a_n \cos(\omega t + d_1(t)) [/tex] and [tex] f_2(t) = \sum b_n cos(\omega t) [/tex] and I would like to find out the value of the phase difference (I've set the phase in [tex]f_2[/tex] equal to zero) at each point in time. Can I get this by comparing the complex parts of the two signal's Fourier transforms? What is the "meaning" of the complex part anyway? Whenever I've used the FT in the past, it's been the absolute value that represents the amplitude of the field at a given frequency, so what are the "meanings" of the real and imaginary parts separately? What is the "meaning" of the phase constructed from the arctan of the ratios of the real and imaginary parts? Thanks for any help you can give me.