Overtone, a sound accompanying the main tone produced by a vibrating body. The number and loudness of overtones determine the timbre, or tone color, of a musical sound. Overtones are present in the human voice and in the sound produced by musical instruments.
When a stretched string is plucked, it vibrates in a number of different ways at the same time. Vibrating as a whole, it produces its lowest tone. This tone is called the string's fundamental, or first harmonic. The string also vibrates in halves, producing a sound with twice the frequency (number of vibrations per second) of the fundamental. This tone—an octave above the fundamental—is called the first overtone, or second harmonic. Vibrating in thirds, the string produces a sound with three times the fundamental frequency. This second overtone, or third harmonic, is one octave plus five whole tones higher than the fundamental. The string vibrates at even higher frequencies, but at each higher frequency, the overtone becomes weaker.