overtone series
The naturally occurring sequence of frequencies (harmonics) that vibrate simultaneously above any fundamental pitch, forming the acoustic basis of all musical timbre and harmony.
In Depth
When any pitched instrument plays a note, it actually produces not just the fundamental frequency but an entire series of higher frequencies (overtones or partials) at integer multiples of the fundamental. A string vibrating at 100 Hz simultaneously produces vibrations at 200, 300, 400, 500 Hz and beyond. The relative strength of these overtones determines the instrument's timbre — why a violin and a flute playing the same note sound different.
The overtone series has profound implications for harmony: the intervals that sound most consonant (octave, fifth, fourth) correspond to the lowest, strongest overtones. Major and minor triads can be derived from the overtone series. Spectral composers like Gérard Grisey and Tristan Murail used the overtone series as the basis for entire compositional systems, building harmonies from the natural resonance of physical sound. The series also explains why brass instruments can only play certain notes without valves, why organ stops combine to create new timbres, and why certain intervals "ring" more than others in a resonant space.
The entire Western system of harmony — major and minor chords, consonance and dissonance, even the twelve-note scale — can be derived from the overtone series, a pattern that exists in the physics of vibrating objects independent of human musical culture.