The Physics Behind Overtone Singing
Overtone Singing is a vocal technique used by singers which creates the perception of singing more than one pitch simultaneously. The technique has been used across many cultures and continents, from Asia to Europe to Africa. Despite being an ancient technique, overtone singing makes use of physics that were only understood much later.
Musical sounds are often generated from a source, such as a string or block, that emits [sound with a harmonic frequency spectrum? - CEW] a series of frequencies when vibrating. The lowest frequency [of a harmonic series - CEW] is referred to in music as the fundamental frequency while the following[higher? - CEW] frequencies are reffered to as the overtones. While the brain tends to perceive the fundamental frequency alone [often associates pitch with the fundamental frequency - CEW], sound waves according to[that have? - CEW] the overtone frequencies are also emitted at varying levels of power..
While the human brain perceives the fundamental frequency and does not naturally distinguish it from its overtones, changes in the emphasis of different overtones create a perceivable change in tone. In music, this tonal quality is often referred to as the timbre, and allows human brains to distinguish between the sounds of different instruments, voices, and other mediums. For vocalists, different syllables and timbres are created through the movement and adjustment of the vocal system, including the vocal folds, jaw movement, lip shape, etc..
How overtone singing is achieved
Overtone singing gives the perception through vocal technique of one of the overtones of a sung fundamental frequency being distinctively heard as well by the human ear. Vocalists who use this technique are also able to give the perception of the movement of the higher frequency to other overtone frequencies, while simultaneously maintaining the fundamental frequency. In many cultures, such as Tuvan culture, overtone singers will create a drone, or a long and constant fundamental lower pitch, while the higher overtones move in a melody above it..
Adept overtone singers achieve the desired effect through altering the shape of the vocal tract, in the same way that most people do so to create syllables in their speech. Singers will change the shape of their vocal tract in order to align the frequency of a formant with that of a harmonic, therefore causing the overtone to resonate more strongly and create a perceivable change [of what? - CEW]. A large number of components in the vocal tract is used to do overtone singing, with manipulations in the larynx and vocal folds, jaw movement to manipulate the volume of the mouth, changing lip shape, as well as the position and thickness of the tongue..
Scientific phenomenon in overtone singing
Overtone singers are able to manipulate the sound of their voice so that the desirable partials in their sound are emitted at comparable, and sometimes much greater loudness than the fundamental frequency. Furthermore, they are able to emit the other undesired partials quietly, so that the fundamental frequency and the overtone are highlighted.
Despite the perception of two frequencies appearing at once during overtone singing, research has shown that in fact two partials that are of close proximity both resonate at high levels on top of the fundamental frequency. Studies have suggested that the distinct clarity and strength of the sung overtones are a result of Helmholtz resonance within the vocal tract, as biologically the vocal tract is not well equipped to produce such high intensity formants due to damping mechanisms, and thus another cause must be the result [how can a cause be a result? do you mean "reason" - CEW].
[Good start. Needs diagrams, and better still, if you could make a sonogram out of a sound file - CEW]
- Hiebert E. The Helmholtz Legacy in Physiological Acoustics. Vol. 39, pp.7 (2014)
- Hiebert E. The Helmholtz Legacy in Physiological Acoustics. Vol. 39, pp.43 (2014)
- Hinds, Stuart. "How to Teach Overtone Singing to Your Choir." The Choral Journal, vol. 51, no. 3, 2010, pp. 34–43., www.jstor.org/stable/23560424.
- Pegg, C. Overtone Singing. "http://www.oxfordmusiconline.com/subscriber/article/grove/music/49849"
- Kob, Malte. "Analysis and Modelling of Overtone Singing in the Sygyt Style." Applied Acoustics 65.12 (2004): 1249-259. Web.