Vibrating strings and columns of air produce not only fundamental frequencies (fundamentals), but also harmonics, frequencies that are integer multiples of the fundamental. The relative intensities of these harmonics, or overtones, impart the predominant flavor to the instrument's characteristic sound, or timbre.
Because the frequency of a sound is inversely proportional to its wavelength, the integer relationship between the fundamental and its overtones can be alternatively stated as a function of wavelength. This relationship then takes the form of the familiar harmonic series:
