By analyzing the sequences of samples and the data contained therein, information can be extracted and plotted on a graph as a spectrum. A general definition of spectrum is “a measure of the distribution of signal energy as a function of frequency”. More simply stated, spectrum is “the combination of the frequencies and their amplitudes that are present in a sound”. Strategies for spectrum analysis fall into two basic categories: static, which is like a snapshot of a spectrum, and time-varying, which is akin to a motion-picture film of a spectrum over time. The most common way to display a time-varying spectrum is to plot a sonogram or spectrogram.