When two waves of same amplitude but differing frequencies are added together, the frequency of the amplitude modulation of the resulting wave is the difference b/w the frequencies of the two parent waves. How about beat frequencies from the interference of more than 2 waves, say 3, 4, or 10? How do we calculate that? Also, it hasn't been clear to me why the two waves need to have the sample amplitude for beat frequency to occur...Isn't beat frequency only a function of the differences in frequencies and not a function of amplitude? Could someone help me clarify these two questions? Thanks!