Abstract of Poster Paper – ICVT 2009
The relationship between laryngeal mechanism and vocal tract
resonance in the music theatre voice: A pilot study.
Tracy Bourne1, Maëva Garnier2
There is a great deal of controversy about the training and production of the music
theatre voice. While the 'belt' voice has recently been a subject of study in a number
of published journals, other common music theatre vocal qualities such as 'legit' and
'mix' have not been well defined in scientific studies to date. A semi-structured
interview was conducted with 12 expert music theatre voice teachers from Australia,
USA, UK and Asia to clarify definitions for these vocal qualities. The teachers
generally agreed that belt is a projected vocal quality, in the chest register, with
forward, 'twangy' vowels, and that legit voice is a vocal quality based in the classical
tradition generally in head register in the female voice, with back vowels and a
greater pitch range than the belt voice. There was a great deal of confusion in regard
to 'mix' amongst the 12 teachers, although the majority agreed that it was a quality
that balanced chest and head registers in the male and female voice.
The following questions emerged from the analysis of interview responses: What are
the acoustic, laryngeal and vocal tract characteristics of belt, legit and mix vocal
qualities? On which dimensions do these modes of production differ?
A pilot study was then conducted to measure registration and resonance strategies of
a single trained subject in 4 music theatre vocal qualities (chesty belt, twangy belt,
mix and legit voice), for three vowels (/a:/, /e/, /ʊ/) and four pitches (A4, B4, C5 and
D5). The normal and shouted voice of this singer was also recorded on the same
three vowels. Audio and electroglottographic (EGG) signals were recorded, as well
as the vocal tract impedance (see Epps et al., 1997). The amplitude of the EGG
signal, the Open Quotient (OQ) of the vocal fold vibration, as well as the ratio of the
amplitude of the closed glottal peak to the open glottal peak was measured. The first
two resonances (R1 and R2) were extracted from the vocal tract impedance. For
each sample, Sound Pressure Level (SPL) as well as the alpha coefficient (α),
defined as the ratio of sound intensity above and below 1000 Hz, were computed
from the audio signal.
From this data, it was verified that the four considered qualities demonstrate
significantly different spectrum characteristics, and that differences in alpha
coefficient do not only come from variations in vocal intensity. A significantly different
OQ for the four qualities was observed: chesty belt shows the lowest OQ, followed by
twangy belt. Both qualities demonstrated an OQ lower than 0.57 suggesting, in
addition to the EGG waveform and amplitude, as well as the ratio of closed peak to
1
University of Ballarat,
t.bourne@ballarat.edu.au
2
Victoria,
Australia;
University
of
Sydney,
Australia.
Email:
Music Acoustics Group, School of Physics, UNSW, Sydney, Australia. Email: mgarnier@unsw.edu.au
open peak, that they were produced in the first laryngeal mechanism (M1). Twangy
belt has a slightly lower EGG amplitude than chesty belt and mix, however the low
OQ value and the high cl pk/op pk suggests that this quality is in M1. In contrast, mix
has an OQ in between legit and belt, suggesting that this singer produced both mix
and legit in the second laryngeal mechanism (M2). However, the more open and
forward placement of R1 and R2 suggest that this singer may be adjusting the vocal
tract to give the impression of a ‘mix’ between M1 and M2 for this quality (Catellengo
et al., 2004). Analysis of the vocal tract resonances show a similarity between belt
and twang qualities, with an adjustment of R1 on the second harmonic (H2) of the
voice up to C5 for /a:/ and /e/, with no adjustments for mix and legit in these vowels.
For the vowel [ʊ], there is a tendency for R1 to follow H2 in chesty and twangy belt,
and for R1 to follow H1 in mix and legit. This is consistent with the fact that the singer
was unable to sing D5 on a /ʊ/ vowel for these two qualities. R1 & R2 frequencies are
higher for twangy and chesty belt than for mix and legit (except for [e]), suggesting a
more open and forward placement for chesty and twangy belt, and a less open and
backward placement for mix and legit. SPL and α values are highest for chesty and
twangy belt, and lower for mix and legit. While SPL and α were not significantly
different between chesty belt and twangy belt, OQ values and EGG amplitude were
lower for twang. This supports the hypothesis that twangy belt may be a more
efficient/safer type of belt than chesty belt.
This pilot study will form the basis of a further study on mechanisms/adjustments and
resonance strategies of 12 male and female professional and student music theatre
singers.
References:
Bourne, T. & Kenny, D (2008). Perceptual descriptions of belt and legit voice qualities in music theatre
(Conference paper). Australian National Association of Teachers of Singing (ANATS), Sing into Spring,
Perth, W.A., Australia.
Castellengo, M., Chuberre, B., Henrich, N. (2004). Is ‘Voix Mixte’, the Vocal Technique Used to Smooth
the Transition across the Two Main Laryngeal Mechanisms, an Independent Mechanism? Proceedings
of ISMA, NARA, Japan.
Epps, J., Smith, J., Wolfe, J., (1997). A novel instrument to measure acoustic resonances of the vocal
tract during speech. Measurement Science and Technology 8: 1112-1121.
Garnier, M., Wolfe, J., Henrich, N., Smith, J. (2008) Interrelationship between vocal effort and vocal tract
acoustics: a pilot study. Proceedings of ICSLP, Brisbane, Australia.
Henrich, N., d’Alessandro, C., Doval, B., Castellengo, M. (2005). Glottal open quotient in singing:
Measurements and correlation with laryngeal mechanisms, vocal intensity, and fundamental frequency.
Journal of the Acoustical Society of America 117(3): 1417-1430.
Henrich, N., Kiek, M., Smith, J., Wolfe, J. (2007). Resonance strategies used in Bulgarian Women’s
singing style: a pilot study. Logopedics, Phoniatrics, Vocology 32(4): 171-177.
Joliveau, E., Smith, J., Wolfe, J., (2004) Tuning of vocal tract resonance of sopranos. Nature 427: 116.
Lovetri, J. (2008). Contemporary Commercial Music. Journal of Voice 22(3): 260-262.
Roubeau, B., Henrich, N., & Castellengo, M. (2009). Laryngeal Vibratory Mechanisms: The notion of
vocal register revisted. Journal of Voice 23(4): 425-438.
Schutte, H., & Miller, D. (1993) Belting and Pop, Nonclassical Approaches to the Female Middle Voice:
Some preliminary conclusions. Journal of Voice 7(2): 142-150.
Sundberg, J., & Nordenberg, M. (2006). Effects of vocal loudness variation on spectral balance as
reflected by the alpha measure of long-term-average spectra of speech. J Acoust Soc Am 120(1): 453457.