Acoustics of the Voice: Registers and Resonances in Singing

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Speaker: Professor Joe Wolfe (University of New South Wales)
Date: 18th May 2012

To cover a large range of pitch and sound level, singers use different registers and different acoustical strategies, oven involving the resonances of the vocal tract. Each of the resonances of the vocal tract can have the effect of boosting the power in a narrow frequency range. To oversimplify, the first two (R1 and R2) are usually associated with different vowels and other phonemes, while R3, R4 and R5 affect timbre, and may be particularly useful to singers wishing to ‘project’ or to radiate in a frequency range in which orchestral power decreases rapidly with frequency. Different vocal mechanisms – different oscillatory behaviour in the larynx – give rise to registers such as modal, falsetto, chest, head and whistle. This talk uses demonstrations and recordings to give an introduction to the acoustics of the voice, concentrating on the work done in our lab, especially on high voices.

For high voices, the wide spacing of harmonics, and the fact that the fundamental frequency f0 can exceed the usual values of R1, require resonance tuning strategies, such as tuning R1 to f0 or, in some cases, to 2f0. As well as improving radiation and significantly increasing output power, this tuning may improve voice stability. Systematic R1:f0 tuning is widely observed in sopranos, whether trained singers or not. One cost is that R1 is then determined by the melody, not the words. However, at least one composer-librettist, Richard Wagner, works to reduce this effect. Resonance tuning is used less systematically by lower voice categories: R1:f0 in the high ranges, and R1:n*f0 in lower ranges.

The upper limit of the usable singing range for sopranos is often the upper limit of R1:f0 tuning: it is difficult to open the mouth wide enough to tune R1 much above 1 kHz (~C6 or the ‘high C’ of sopranos), and it is difficult to sing loudly without resonance tuning. Above about C6, in the high range used by coloratura sopranos and some jazz and pop singers, R2 may be tuned to f0, offering another octave or more using the M3 mechanism.

Sopranos can make a transition from their head voice (mechanism M2) to the whistle voice (M3) somewhere around C6, and some are able to displace it and thus to sing with two different qualities over an overlap range. The different combinations of mechanism and tuning strategy give singers, especially sopranos, a range of possible styles and solutions to musical problems.

This work reports collaborations with a number of colleagues and students, especially Maëva Garnier, Nathalie Henrich and John Smith. The lab’s web site is at www.phys.unsw.edu.au/music/