Course:PHYS341/Archive/2016wTerm2/OvertoneSinging

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Tibetan monks performing traditional throat singing.

Throat singing (also known as overtone singing) is an ancient chanting technique which has been practiced in Tibet for hundreds of years. It is deeply rooted in Buddhist tradition and creates unique sound by giving the listener the impression they are hearing two pitches when the singer is actually only producing one[1]. Overtone singing is practiced across the globe, from the Inuits in Northern Canada to Mongolian steppe. Tibetan overtone singing distinguishes itself from other forms of overtone singing by principally using the lowest fundamentals possible. The three most common types of throat chanting/singing in Tibet are Gyuke, Dzoke, and Gyer.

Tibetan monks do not actually produce two pitches while throat singing, even though it seems that way to the human ear. The phenomenon occurs because the singers distinguish a fundamental and one of its overtones(also known as partials) as two distinct pitches rather than one. The fundamental frequency they produce is often referred to as the “drone”, and its harmonics the melody[2]. The monks manipulate cavities throughout their vocal tract such as the mouth and larynx to change the resonances of their sounds. The ability for listeners to discern the pitch of an overtone from its fundamental is unique because listeners almost always hear a single pitch corresponding to the fundamental, with its partials only affecting its quality[3]. The physical technicalities of how overtone singing is achieved are still subject to ongoing research.

Reinforcing the overtones

When an oscillator is excited, it will naturally vibrate at a set of frequencies. The lowest is known as the fundamental, while the higher frequencies are known as overtones. By adjusting the vocal tract, throat singers are able to improve their timbre. The quality of sound produced by any singer is largely due to their ability to manipulate the chambers in which resonance occurs throughout the vocal tract. The process of making the fundamental frequency’s overtone distinguishable to the human ear is often referred to as “reinforcement”[4] [5]. This includes making the desired overtone louder through resonance while simultaneously quieting undesired overtones. Tibetan throat singers use two basic mechanisms to reinforce the overtone.

The Larynx Longitudinal resonance

A diagram of the upper vocal tract and the larynx

The first step in reinforcing the formant is by creating a longitudinal resonator within the larynx. This resonator (which is almost closed at both ends) occurs between the vocal folds and about 140mm before the glottis[6]. The purpose of this is to manipulate the vocal tract so it can “align” the frequencies of a harmonic and its formant. This specifically helps reinforce the formants since the larynx is so small it only resonates high frequencies; research suggests that the ideal overtone frequency is around 2800 to 3200 Hz[7]. This is key for separating the higher overtones from the fundamental.

The Mouth Helmholtz Resonance

A diagram demonstrating the similarities between a mouth and a Helmholtz resonator.

The overtone effect is greatly amplified because the mouth of the singer acts as a Helmholtz resonator. The “resonator” can be tuned by closing or widening the opening of the singer’s mouth, or by extending or contracting the singer’s lips. In both of these cases the opening of the mouth is the equivalent of the bottle neck in a “true” Helmholtz resonator, which determines the pitch[8]. Closing the opening makes the overtone softer, and widening the makes it louder[9]. This Helmholtz resonating effect greatly enhances the overall quality of the overtone by amplifying the resonance of the singer’s longitudinal vocal tract[10]. The superior resonating from the combined two mechanics allows the harmonics to be sung at a higher volume than fundamental. Without the resonating, the overtone would simply blend in with the fundamental as in standard singing techniques. How the singer uses their jaw and tongue are also key to explaining throat singing, but their uses are separate from the overall Helmholtz structure their mouth makes. Researchers believe the tongue is principally used to articulate and optimize the overtone sound. Moving the jaw backwards and forwards can help change the overall volume of the singing[11].


References

  1. Franz, Julia. "See how Tuvan throat singers can sing multiple notes at once." Public Radio International. N.p., 28 Mar. 2017. Web. 06 Apr. 2017.
  2. Kob, Malte. "Analysis and modelling of overtone singing in the sygyt style." Applied Acoustics 65.12 (2003): 1249-259. Web.
  3. White, Harvey E., and Donald H. White. Physics and Music: The Science of Musical Sound. New York: Dover Publications Inc, 2014. Print.
  4. Titze, Ingo R. “Nonlinear Source–filter Coupling in Phonation: Theory.” The Journal of the Acoustical Society of America 123.5 (2008): 2733–2749. PMC. Web. 21 Mar. 2017.
  5. Kob, Malte. "Analysis and modelling of overtone singing in the sygyt style." Applied Acoustics 65.12 (2003): 1249-259. Web.
  6. Kob, Malte. "Analysis and modelling of overtone singing in the sygyt style." Applied Acoustics 65.12 (2003): 1249-259. Web.
  7. Sundberg, Johan(1974). Articulatory interpretation of the "singing formant". J Acoust Soc Am. 1974 Apr;55(4):838–844.
  8. Kob, Malte. "Analysis and modelling of overtone singing in the sygyt style." Applied Acoustics 65.12 (2003): 1249-259. Web.
  9. Pegg, Carole. "Overtone-singing [throat-singing, chant biphonique, chant diphonique, höömii]." Overtone-singin in Oxford Music Online. Oxford Music, n.d. Web.
  10. Kob, Malte. "Analysis and modelling of overtone singing in the sygyt style." Applied Acoustics 65.12 (2003): 1249-259. Web.
  11. Pegg, Carole. "Overtone-singing [throat-singing, chant biphonique, chant diphonique, höömii]." Overtone-singin in Oxford Music Online. Oxford Music, n.d. Web.