 Signals are built out of sine waves, at least according to the Fourier transform. But what are the properties of a sine wave? Well, there are three – amplitude, frequency and phase. In sound signals, the amplitude of a sine wave tells us how loud it is, the frequency of a sine wave tells us its pitch and the phase of a sine wave tells us its position within the signal. Imagine I had two sine waves at different frequencies added together. If I change the phase of the second sine wave relative to the first, it changes the shape of the signal. The Fourier transform analyses a signal by breaking it apart into its individual sine waves and tells us the amplitude, frequency and phase of each sine wave making up the signal.