Definition of an Overtone
An overtone is any frequency higher than the fundamental frequency of a sound, typically a musical note, that is produced by an oscillating source. These additional frequencies vibrate simultaneously with the fundamental, contributing to the sound's unique timbre or tone color.
Generation of Overtones
When an object vibrates, it doesn't just move as a whole at its slowest, loudest frequency (the fundamental). It also vibrates in smaller segments, such as halves, thirds, or quarters of its length. Each of these smaller, faster vibrations produces a higher frequency, which are the overtones. For instance, a vibrating guitar string produces its fundamental pitch, but also quieter, higher pitches from its segments.
Importance in Timbre and Sound Quality
The specific combination and relative amplitudes of a sound's fundamental frequency and its various overtones are what determine its timbre. This is why a flute, a piano, and a human voice can all produce the same note (the same fundamental frequency) but sound distinctly different. The unique blend of overtones gives each sound source its characteristic sonic identity.
Overtones vs. Harmonics
While often used interchangeably, there's a technical distinction: all harmonics are overtones, but not all overtones are harmonics. A harmonic is an overtone whose frequency is an exact integer multiple (e.g., 2x, 3x, 4x) of the fundamental frequency. Most Western musical instruments produce largely harmonic overtones, which sound consonant and pleasing. Inharmonic overtones, not exact integer multiples, are common in percussion instruments like bells and drums, contributing to their complex or percussive sound.