Harmonic spectrum

A harmonic spectrum is a spectrum containing only frequency components whose frequencies are whole number multiples of the fundamental frequency; such frequencies are known as harmonics. "The individual partials are not heard separately but are blended together by the ear into a single tone."

In other words, if $$\omega$$ is the fundamental frequency, then a harmonic spectrum has the form
 * $$\{\dots, -2\omega, -\omega, 0, \omega, 2\omega, \dots\}.$$

A standard result of Fourier analysis is that a function has a harmonic spectrum if and only if it is periodic.