The overtone series (the natural, or harmonic, series) is a fundamental acoustic phenomenon: almost every musical sound in fact consists not of a single frequency but of a fundamental tone and a whole succession of quieter partials — overtones — that sound above it according to a strictly defined natural law.
It is the ratio and loudness of these overtones that determine timbre — the inimitable “colouring” of a sound by which we tell a violin from a flute, or one voice from another. The overtone series also underlies harmony: the first, strongest overtones form the octave, the fifth, and the third — the most consonant intervals. This phenomenon is also the basis of playing “natural” instruments without valves (the horn, the military bugle) and the Ukrainian overtone flute telynka, where the scale is produced by overblowing and by closing or opening the pipe with a finger.
