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Overtone singing – also known as overtone chanting, harmonic singing, polyphonic overtone singing, and diphonic singing – is a set of singing techniques in which the vocalist manipulates the resonances of the vocal tract, in order to arouse the perception of additional, separate notes beyond the fundamental frequency being produced.
From a fundamental pitch, made by the human voice, the belonging harmonic overtones can be selectively amplified by changing the vocal tract, i.e. the dimensions and shape of the resonant cavities of the mouth and the pharynx. This resonant tuning allows singers to create more than one pitch at the same time (the fundamental and one or more selected overtones), while usually generating a single fundamental frequency with their vocal folds.
Overtone singing should not be confused with throat singing, in spite of the fact that many throat singing techniques comprise overtone singing. As mentioned, overtone singing involves the careful manipulations of the vocal tract, whereas throat singing is mostly related to the voice source.