Can a generic, not necessarily harmonic, signal of time be represented as a complex signal with a real and imaginary part? Usually the complex rappresentation is used for time harmonic signals and linear systems. The "real" time signal is transformed into a complex signal. At the end of the mathematical operations, it is possible to look at the real or imaginary part of the complex signal and get the correct results for the initial signal. But what if the starting real signal is not harmonic? thanks!