An overtone is any resonant frequency produced by a vibrating object that sits above its lowest, fundamental frequency. When a guitar string vibrates, you hear the fundamental pitch most prominently, but the string is simultaneously producing a stack of higher frequencies on top of it. Those higher frequencies are overtones, and they’re the reason a piano and a violin playing the same note sound completely different.
How Overtones Relate to Frequency
Every vibrating object, whether it’s a vocal cord, a guitar string, or a column of air inside a flute, has a fundamental frequency. That’s the lowest frequency at which it naturally vibrates, and it’s what your ear identifies as the “note.” But the object doesn’t vibrate at just one frequency. It also vibrates in smaller segments, producing frequencies that are higher than the fundamental.
For most string and wind instruments, these overtones follow a simple mathematical pattern called the harmonic series. If the fundamental frequency is f, the overtones stack up as 2f, 3f, 4f, 5f, and so on. The first overtone vibrates at twice the fundamental frequency, which sounds exactly one octave higher. The second overtone vibrates at three times the fundamental, producing a note a perfect fifth above that octave. The pattern continues upward, with each new overtone adding another integer multiple of the original frequency.
These whole-number frequency ratios are the physical basis of musical consonance. When two notes share many overtones in common, they tend to sound pleasant together. That’s not a cultural preference; it’s a consequence of how vibrating objects naturally behave.
Overtones vs. Harmonics
The terms “overtone” and “harmonic” overlap but aren’t identical. A harmonic is specifically an integer multiple of the fundamental frequency: the second harmonic is 2f, the third is 3f, and so on. The fundamental itself counts as the first harmonic. An overtone, by contrast, refers to any resonant frequency above the fundamental, whether or not it falls on one of those neat integer multiples.
This creates a numbering offset that trips people up. The first overtone is the second harmonic (2f). The second overtone is the third harmonic (3f). The fundamental is the first harmonic but is not an overtone at all, since it’s not “over” anything.
For instruments that use strings or air columns, the distinction rarely matters because their overtones are harmonic. They line up with the integer multiples almost perfectly. But percussive instruments like drums and bells often produce overtones that land between those integer multiples. A cymbal’s shimmering, complex sound comes from overtones that don’t fit the harmonic series cleanly. These are called inharmonic overtones, and they give percussion its characteristically noisy, less pitch-defined quality.
Why Instruments Sound Different
If a flute and a trumpet both play a concert A at 440 Hz, the fundamental frequency is identical. What makes them sound distinct is the relative strength of each overtone. A flute produces a tone dominated by the fundamental with relatively weak overtones, giving it a pure, clear quality. A trumpet generates strong overtones across a wide range, creating a brighter, brassier sound. This unique recipe of overtone strengths is called timbre, and it’s essentially the fingerprint of an instrument’s voice.
Audio engineers and music producers think about overtones in terms of even and odd groupings. Even-numbered overtones (2f, 4f, 6f) tend to add warmth, fullness, and a smooth quality to a sound. Odd-numbered overtones (3f, 5f, 7f) contribute brightness, clarity, and a more aggressive edge. This is why tube amplifiers, which naturally emphasize even harmonics, are prized for their warm sound, while certain types of distortion that emphasize odd harmonics produce a harder, grittier tone favored in rock and electronic music.
When Overtones Don’t Behave Perfectly
The neat mathematical model of the harmonic series assumes that strings are perfectly flexible, bending without any resistance. Real strings are made of stiff metal or nylon, and that stiffness causes their overtones to land slightly higher than the exact integer multiples predicted by theory. This effect is called inharmonicity.
Piano tuners deal with this constantly. Shorter, thicker, and looser strings exhibit more inharmonicity because they resist bending more strongly. The bass and treble ends of a piano keyboard, where strings are either very thick or very short, are the most affected. If a tuner sets two notes to a mathematically perfect octave (a precise 2:1 frequency ratio between fundamentals), the slightly sharp overtones of the lower note will clash with the fundamental of the upper note. The result sounds out of tune to the ear, even though the math says it shouldn’t. To compensate, piano tuners use “stretched tuning,” deliberately tuning the highest notes slightly sharp and the lowest notes slightly flat so the overtones of adjacent notes align more naturally.
Overtone Singing
One of the most striking demonstrations of overtones in action is Tuvan throat singing, a vocal tradition from Central Asia in which a single singer produces two distinct pitches at once. The lower pitch is the fundamental, generated by the vocal cords vibrating normally. The higher pitch, a clear, whistle-like tone floating above the drone, is a single overtone that the singer has isolated and amplified.
Research published in eLife revealed how this works mechanically. Throat singers create two precise constrictions in the vocal tract: one where the tip of the tongue nearly touches a bony ridge on the roof of the mouth, and another formed by the base of the tongue farther back. These two constrictions merge two natural resonance peaks of the vocal tract into one, creating a very narrow amplification window in the 1,000 to 2,000 Hz range. That window selectively boosts a single overtone from the rich spectrum of frequencies coming off the vocal cords, making it loud enough to hear as a separate melody. Very small, targeted movements of the tongue shift which overtone gets amplified, allowing the singer to play a tune using nothing but the physics already present in their voice.
Overtone singing illustrates something fundamental about all sound: the overtones are always there. Every sung vowel, every plucked string, every blown note contains a tower of frequencies stacked above the one you consciously hear. What changes is which overtones get emphasized and which get suppressed, and that single variable accounts for an enormous range of sonic variety.