Some singers can produce two notes at once with a single voice.
In Tuva, Mongolia and beyond, overtone singers hold a low drone while a second, whistling melody floats above it. They don't have two voices. They reshape their mouth and throat to amplify individual harmonics that are already hidden inside every sung note, and pick out tunes from them.
Every note the human voice sings is a blend of frequencies: a fundamental pitch plus a series of fainter overtones, or harmonics, at whole-number multiples of it. Normally we hear them fused as one sound with a particular colour. Overtone singers change the size and shape of the resonating spaces in the mouth and pharynx so that one harmonic at a time is boosted until it stands out as a separate, flute-like pitch.
The art is thought to have originated in Central Asia, in Tuva, Altai and Mongolia; Mongolia is often considered its most active home today. Tuvan singers use a range of styles, including khöömei, the high whistling sygyt, and the deep, growling kargyraa, which adds a second sound source from the false vocal folds. Their melodies traditionally use the 6th, 8th, 9th, 10th, 12th and 13th harmonics, which form a major pentatonic scale, while carefully skipping the 7th and 11th.
Overtone singing is sometimes lumped together with throat singing, but they are not the same: overtone singing is about shaping the vocal tract, while many throat-singing styles alter the voice at its source. Related traditions turn up in many places: the chanting of Tibetan Buddhist monks, Sardinia's four-man cantu a tenore choirs, recognised by UNESCO in 2005, and the umngqokolo singing of some Xhosa women in South Africa.
Western musicians took it up from the 1960s. Karlheinz Stockhausen's Stimmung of 1968 was among the first classical works to use it. The documentary Genghis Blues, about the American blues musician Paul Pena travelling to a throat-singing contest in Tuva, won at Sundance in 1999. In 2014 the German singer Anna-Maria Hefele went viral with a video demonstrating polyphonic overtone singing.
Source: Wikipedia — Overtone singing · Text summarised from Wikipedia (CC BY-SA 4.0)
