While this might seem to be an unduly simplified approach, id has definite advantages, In a complex system tones are often the only signals that are traceable; they facilitate the calculation of spectra, bandwidths, signal that are traceable; they facilitate the calculation of spectra, bandwidths, signal power, and so forth, that would otherwise be impossible to trace. Furthermore, if we can find the response of a communication system to a specific frequency in the message band, then we can infer the response for all frequencies in the message band.