Adjustment of Glottal Configurations in Singing
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Adjustment of Glottal Confgurations in Singing Christian T. Herbst and Jan G. Švec INTRODUCTION ocal timbre is the central quality in singing. On a long-term level basis, singers and their teachers are concerned with “building the instrument,” that is, establishing habitual motor control and behavioral patterns for voice production Vwithin the limits of their chosen singing style (this process is well refected by the German term Stimmbildung). On the other hand, singers must also be able to vary voice timbre on an ad hoc level, allowing for artistic Christian T. Herbst expression. Here, agility and muscular fne control are the main features of a “good” voice. Te human voice production mechanism consists of three basic physi- ological layers: the respiratory system (power source), the larynx (sound source), and the vocal tract (sound modifers).1 Te most obvious method for voice timbre control is via the sound modifers, that is, articulation by introducing changes into the vocal tract shape.2 Fine tuning the vowel color (in relation to pitch) is a well established concept for varying the vocal timbre and optimizing sound output in singing.3 At the laryngeal (sound source) level, vocal timbre can be modifed by two Jan G. Švec basic physiological adjustments: (1) adduction of the posterior (cartilaginous) glottis, controlled by the singer when changing the quality of voice between “breathy” and “pressed”;4 and (2) via the singing voice register.5 Whereas each of these physiological parameters (adduction of the posterior glottis and vocal registers) is well researched and understood individually, little is known about their relation to each other. Tis is particularly true in the realm of voice pedagogy, where the proper terminology is not well estab- lished and sometimes not well comprehended. It is therefore desirable to fll this gap in our understanding of the singing voice by attempting to relate the two concepts to each other. TWO TYPES OF GLOTTAL ADDUCTION Te glottis can be conceptually divided into two parts: the membranous glottis (i.e., the portion made up of the vocal folds from the anterior commissure Journal of Singing, January/February 2014 to the tip of the vocal processes); and the cartilaginous glottis (i.e., the poste- Volume 70, No. 3, pp. 301–308 Copyright © 2014 rior part of the glottis, consisting of the arytenoid cartilages and their vocal National Association of Teachers of Singing processes; see Figure 1b). January/February 2014 301 Christian T. Herbst and Jan G. Švec Figure 1. Schematic illustration of two types of glottal adduction: (a) membranous medialization; middle and bottom graph: coronal section through larynx, showing the efect of TA muscle contraction; (b) conceptual separation of glottis into membranous and cartilaginous portion; (c) cartilaginous adduction. A closer examination of the two glottal adjustments the vocal folds; in particular, it bulges out the inferior revealed a causal relationship between (1) the singer’s portion of the vocal fold, and also reduces the width of intended sound quality; (2) the muscular adjustments the membranous glottis.7 Tis maneuver can be called made in the larynx; (3) their impact on glottal adduc- membranous medialization through vocal fold bulging tion (membranous and/or cartilaginous glottis); (4) the (short: membranous medialization).8 A contraction of vibratory properties of the vocal folds and their efect the TA increases the vertical phase delay in vocal fold on glottal airfow; and (5) the actual sound that is being vibration and results in a longer closed phase (and thus a produced. larger closed quotient).9 From an acoustic point of view, Te chest vs. falsetto register is mainly controlled this enhances the output of high-frequency energy,10 via the thyroarytenoid (TA, vocalis) muscle (see Figure thus creating a “brighter” or more “resonant” timbre. 1a). Whereas in falsetto the TA is more or less relaxed, This is perceived as a “heavier” registration by both it is contracted in chest (particularly at higher pitches), singers and listeners. thus thickening, shortening, and medially bulging the Te voice quality along the dimension of “breathy” body of the vocal fold, while slackening the vocal fold vs. “pressed” is maintained through the adductors, that cover.6 Te medial bulging of the membranous portion is, the lateral cricoarytenoid (LCA) and interarytenoid of the vocal fold adducts the membranous portion of (IA) muscles, and their antagonist, the posterior cri- 302 Journal of Singing Adjustment of Glottal Confgurations in Singing Figure 2. Schematic illustration of the efect of cartilaginous adduction and membranous medialization through vocal fold bulging in singing. For each adduction type, two schematic graphs are shown: top view of vocal folds, arytenoids, and thyroid cartilage (lef); sagittal view of larynx, with schematic drawings of thyroid cartilage, cricoid cartilage, and thyroarytenoid muscle (right). Te arrows indicate the primary changes in the vocal fold position for each case. Te expected theoretical contributions of the internal laryngeal muscles (TA, LCA, and IA) on the three dimensional airspace of the glottis are also indicated. Te main action of the TA is to bulge out the inferior portion of the vocal fold; the LCA adducts the vocal processes and thus also the superior membranous portion of the vocal fold (indicated by the small gray arrows in aDducted falsetto); and the IA seals the posterior cartilaginous glottis (Christian T. Herbst, Qingjun Qiu, Harm K. Schutte, and Jan G. Švec, “Membranous and Cartilaginous Vocal Fold Adduction in Singing,” Journal of the Acoustical Society of America 129, no. 4 [April 2011]: 2253–2262; used with permission). coarytenoid (PCA) muscle, which is an abductor (see tis (caused by the efect of LCA activity on the superior Figure 1c).11 Te main efect of activity in the LCA and part of the membranous vocal fold portion). Tis is due IA muscles is the adduction of the cartilaginous glottis to the fact that the vocal folds terminate posteriorly at via the positioning of the arytenoid cartilages. Whereas the vocal processes of the arytenoid cartilages, hence any the LCA adducts the vocal processes (and hence also the manipulation of the cartilaginous glottis is propagated superior membranous portion of the vocal folds), the to a some extent to the membranous glottis. A higher IA muscles seal the posterior part of the cartilaginous degree of cartilaginous adduction results in a longer glottis. Te maneuver induced by the combined action closed phase (and thus a larger closed quotient),15 creat- of LCA and IA is thus termed cartilaginous adduction.12 ing stronger high frequency components in the radiated Te cartilaginous glottis can either be fully adducted, or sound.16 there can be a posterior glottal chink (PGC) of variable Schematically, these two types of glottal adduction size.13 In the latter case, vocal fold contact during a glottal (cartilaginous adduction and membranous medializa- cycle is reduced or nonexistent, which results in a steady tion) and the resulting glottal confgurations, as well as airflow during the “pseudo” closed phase, therefore the expected roles of the internal laryngeal muscles, are introducing noise components into the voice source.14 displayed in Figure 2. It should be noted that no single As a side efect, cartilaginous adduction also has an muscle adducts one and only one compartment of the infuence on the confguration of the membranous glot- vocal folds, particularly when considering the vertical January/February 2014 303 Christian T. Herbst and Jan G. Švec TABLE 1. Four distinct phonation types, as created by dif- muscle tension dysphonia.18 On the other hand, falsetto ferent degrees of cartilaginous adduction and membranous register (where the thyroarytenoid muscle is relaxed) medialization. can be produced with full closure of the posterior glottis, Cartilaginous Membranous such as in the mid and upper range of trained female Voice quality adduction medialization classical singing, and in countertenor singing. Te timbral efect of variations of the closed phase can aBducted falsetto — — aDducted falsetto ++ — be observed in the spectra shown in the bottom of Figure aBducted chest — ++ 3. When going from aBducted falsetto to aDducted chest, aDducted chest ++ ++ the ever increasing duration of the closed phase correlates with a decreasing spectral slope, resulting in stronger high frequency components in the acoustic signal for dimension of the membranous portion of the vocal folds. phonations with more adduction of the cartilaginous However, these fner aspects of vocal fold geometry are or membranous glottis (i.e., a “heavier registration”).19 not relevant for the creation of a basic pedagogic model, which should have the potential to be applied easily in TWO TYPES OF ADDUCTION— both singing pedagogy and speech therapy. A PEDAGOGIC MODEL Recently it has been shown that both trained and untrained singers can separately infuence the degree of Since cartilaginous adduction and membranous medial- cartilaginous adduction and membranous medialization, ization can be controlled separately by both trained and thus being able to create four distinct voice qualities by untrained singers, these two physiological parameters four distinct glottal confgurations: aBducted falsetto can be displayed in a two dimensional plane in order (FaB), aDducted falsetto (FaD), aBducted chest (CaB) to create a pedagogic model for sound quality adjust- and aDducted chest (CaD; Table 1 and Figure