NCVS Insights – Science that Resonates
Searching for the Causes of Chest-Falsetto Register Breaks Under Anechoic Conditions
November 23, 2024
Volume 2 Issue 6 – November 2024
by
Since the beginning of the 21st century, it has been recognized that the acoustic resonances of the vocal tract and of the subglottal tract can interact with the vocal fold vibrations and can trigger register breaks (2, 3). This discovery brought upon the question whether chest-falsetto breaks would occur also in the absence of vocal tract and subglottal tract resonances. Excised larynx experiments were able to eliminate vocal tract resonances and showed that register breaks occur also without the vocal tract (1). Subglottal resonances could not be eliminated, however, since the air must be delivered through a subglottal tract to make the vocal folds oscillate. Therefore, we constructed a special anechoic subglottal tract that eliminates the subglottal resonances (4). Using the anechoic subglottal tract and no vocal tract, we were able to perform excised larynx experiments in fully anechoic conditions where we smoothly elongated and shortened the vocal folds and observed whether the voice breaks occur or not (5). The experiments showed that chest-falsetto register breaks occur also in anechoic conditions, and that no new breaks occur when subglottal resonances are present. This brings the definite proof that the primary cause of the chest-falsetto breaks is not in the interactions with the subglottal or vocal tract resonances, but it is rather inherent to the vocal fold oscillatory properties. Nevertheless, the subglottal resonances changed the starting and ending pitches of the breaks when present, so their influence should not be neglected, similarly as the influence of the vocal tract. The big question is, what allows the chest-falsetto transition to be smoothened out? Careful experiments such as these bring us closer towards answering this question.
Figure 1. Left: Schematic of the excised larynx setup with resonant and anechoic subglottal tract, without a vocal tract. Right: Results of the measurements of six upward jumps from chest to falsetto registers in an excised human larynx in anechoic and resonant conditions. The jumps were elicited by smooth elongation of the vocal folds. Notice that the jumps vary among attempts and the landing frequency of the jump is higher in resonant than in anechoic conditions. The dashed horizontal lines show the median of the frequencies before and after the jump of the six attempts and the gray horizontal lines show the integer fractions of the acoustic resonance frequency of the subglottal tract, which was set to 500 Hz. For more details, see (5).
REFERENCES
Švec JG, Schutte HK, Miller DG. On pitch jumps between chest and falsetto registers in voice: data from living and excised human larynges. J Acoust Soc Am. 1999;106(3, Pt.1):1523-31.
Titze I, Riede T, Popolo P. Nonlinear source-filter coupling in phonation: Vocal exercises. J Acoust Soc Am. 2008;123(4):1902-15.
Titze IR. Nonlinear source-filter coupling in phonation: Theory. J Acoust Soc Am. 2008;123(5):2733-49.
Lehoux S, Hampala V, Švec JG. Subglottal pressure oscillations in anechoic and resonant conditions and their influence on excised larynx phonations. Sci Rep. 2021;11(1):Art. no. 28; 1-14.
Lehoux S, Herbst CT, Dobiáš M, Švec JG. Frequency jumps in excised larynges in anechoic conditions: A pilot study. Journal of Sound and Vibration. 2023;551:1-8, Art. no. 117607.
Jan Švec
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More than a decade ago, I accidentally discovered Dr. Zhaoyan Zhang’s work on the three-dimensional model of fold oscillation. I did not understand the physics but the concept was clear. This revolutionized my work as a vocal pedagogue. I would suggest that the dynamic nature of vocal fold posturing makes smooth registration very difficult but some singers learn by ear and copy smooth registration very well with little training. Speech habits contribute as well. The main factor, I believe, could be the multilateral nature of fold closure. LCA, IA and TA groups must all coordinate for “deep and complete closure of the folds” (what I call the traditional operatic model of phonation). Posterior elongation via the PCA is tricky because that muscle also has the primary function of abduction. In such a scenario, subglottal pressure could change radically with fold elongation.
If however the phonation model is not “traditional operatic” it could be easier to produce a smoother registration. Rossini tenors tend to produce a less rich timbre, whereby closure is concentrated on the function of the LCA and also less rectangular (i.e. more superficial) posture (less TA resistanceto elongation). It’s possible in this scenario that the posterior gap remains open (IA inefficiency). This dynamic is much less complicated and easier to coordinate. However, the sound is usually less rich and lacking in Singer’s Formant strength.