overtone

An overtone is any frequency component of a periodic sound that lies above the fundamental frequency. The set of overtones includes harmonic partials at 2f0, 3f0, 4f0, and so on; these are collectively known as the harmonic series. The fundamental, f0, determines the perceived pitch, while the overtones shape timbre.

Overtones arise from the physics of vibrating bodies and air columns. When a string, air column, or membrane vibrates, it tends to support specific modes of vibration with frequencies that are integer multiples of the fundamental. The relative amplitudes of these partials depend on material, geometry, excitation, and boundary conditions, leading to unique timbres for different instruments or voices. In some cases, the spectrum includes non-integer (inharmonic) partials, especially in bells or piano strings under certain conditions.

Perceptually, listeners identify timbre from the overtone content and its spectral envelope; even if two instruments play the same note at the same loudness, different overtone patterns produce distinct sounds. Overtone singing is a technique in some vocal traditions in which the singer emphasizes a particular overtone to create a second pitch above the fundamental.

In music analysis and acoustics, the term overtone is used to describe frequencies above the fundamental, with harmonics referring specifically to integer-multiple partials. The study of overtones explains much of why instruments with the same pitch can sound so different and how timbre is produced and perceived.