## The frequency domain

#### The representation of a time domain signal by a summation of sine or cosine components is usually referred to as the spectrum of the waveform. It is traditional to draw the spectrum as discrete lines on a graph, with the position of the lines on the x-axis representing the frequency of the component, and the height of the line representing the amplitude. Again, it is common practice to represent only the absolute value or magnitude of each component in the spectrum, however, one must not forget that in fact each term in the Fourier Series expansion could be made up of both sine and cosine terms at any given frequency and hence both magnitude and phase are required for a complete representation of the time domain signal. |

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