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Journal of Singing, January/February 2014Volume 70, No. 3, pp. 301–308Copyright © 2014 National Association of Teachers of Singing

Jan G. Švec

Christian T. Herbst

Adjustment of Glottal Configurations in SingingChristian T. Herbst and Jan G. Švec

INTRODUCTION

V 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

within the limits of their chosen singing style (this process is well reflected 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

expression. Here, agility and muscular fine control are the main features of a “good” voice.

The 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 modifiers).1 The most obvious method for voice timbre control is via the sound modifiers, 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 modified by two 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. This 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 fill this gap in our understanding of the singing voice by attempting to relate the two concepts to each other.

TWO TYPES OF GLOTTAL ADDUCTION

The 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 to the tip of the vocal processes); and the cartilaginous glottis (i.e., the poste-rior part of the glottis, consisting of the arytenoid cartilages and their vocal processes; see Figure 1b).

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A closer examination of the two glottal adjustments revealed a causal relationship between (1) the singer’s intended sound quality; (2) the muscular adjustments made in the larynx; (3) their impact on glottal adduc-tion (membranous and/or cartilaginous glottis); (4) the vibratory properties of the vocal folds and their effect on glottal airflow; and (5) the actual sound that is being produced.

The chest vs. falsetto register is mainly controlled via the thyroarytenoid (TA, vocalis) muscle (see Figure 1a). Whereas in falsetto the TA is more or less relaxed, it is contracted in chest (particularly at higher pitches), thus thickening, shortening, and medially bulging the body of the vocal fold, while slackening the vocal fold cover.6 The medial bulging of the membranous portion of the vocal fold adducts the membranous portion of

the vocal folds; in particular, it bulges out the inferior portion of the vocal fold, and also reduces the width of the membranous glottis.7 This maneuver can be called membranous medialization through vocal fold bulging (short: membranous medialization).8 A contraction of the TA increases the vertical phase delay in vocal fold vibration and results in a longer closed phase (and thus a larger closed quotient).9 From an acoustic point of view, this enhances the output of high-frequency energy,10

thus creating a “brighter” or more “resonant” timbre. This is perceived as a “heavier” registration by both singers and listeners.

The voice quality along the dimension of “breathy” vs. “pressed” is maintained through the adductors, that is, the lateral cricoarytenoid (LCA) and interarytenoid (IA) muscles, and their antagonist, the posterior cri-

Figure 1. Schematic illustration of two types of glottal adduction: (a) membranous medialization; middle and bottom graph: coronal section through larynx, showing the effect of TA muscle contraction; (b) conceptual separation of glottis into membranous and cartilaginous portion; (c) cartilaginous adduction.

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coarytenoid (PCA) muscle, which is an abductor (see Figure 1c).11 The main effect of activity in the LCA and IA muscles is the adduction of the cartilaginous glottis via the positioning of the arytenoid cartilages. Whereas the LCA adducts the vocal processes (and hence also the superior membranous portion of the vocal folds), the IA muscles seal the posterior part of the cartilaginous glottis. The maneuver induced by the combined action of LCA and IA is thus termed cartilaginous adduction.12

The cartilaginous glottis can either be fully adducted, or there can be a posterior glottal chink (PGC) of variable size.13 In the latter case, vocal fold contact during a glottal cycle is reduced or nonexistent, which results in a steady airflow during the “pseudo” closed phase, therefore introducing noise components into the voice source.14

As a side effect, cartilaginous adduction also has an influence on the configuration of the membranous glot-

tis (caused by the effect of LCA activity on the superior part of the membranous vocal fold portion). This is due to the fact that the vocal folds terminate posteriorly at the vocal processes of the arytenoid cartilages, hence any manipulation of the cartilaginous glottis is propagated to a some extent to the membranous glottis. A higher degree of cartilaginous adduction results in a longer closed phase (and thus a larger closed quotient),15 creat-ing stronger high frequency components in the radiated sound.16

Schematically, these two types of glottal adduction (cartilaginous adduction and membranous medializa-tion) and the resulting glottal configurations, as well as the expected roles of the internal laryngeal muscles, are displayed in Figure 2. It should be noted that no single muscle adducts one and only one compartment of the vocal folds, particularly when considering the vertical

Figure 2. Schematic illustration of the effect 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 (left); sagittal view of larynx, with schematic drawings of thyroid cartilage, cricoid cartilage, and thyroarytenoid muscle (right). The arrows indicate the primary changes in the vocal fold position for each case. The expected theoretical contributions of the internal laryngeal muscles (TA, LCA, and IA) on the three dimensional airspace of the glottis are also indicated. The 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).

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dimension of the membranous portion of the vocal folds. However, these finer aspects of vocal fold geometry are not relevant for the creation of a basic pedagogic model, which should have the potential to be applied easily in both singing pedagogy and speech therapy.

Recently it has been shown that both trained and untrained singers can separately influence the degree of cartilaginous adduction and membranous medialization, thus being able to create four distinct voice qualities by four distinct glottal configurations: aBducted falsetto (FaB), aDducted falsetto (FaD), aBducted chest (CaB) and aDducted chest (CaD; Table 1 and Figure 3).17

As expected, the main difference between the aBducted phonations and their aDducted counterparts was observed in the configuration of the posterior glot-tis. All the subjects had a greater posterior glottal chink and thus a less adducted cartilaginous glottis in the two aBducted (breathy) phonation types (“aBducted fal-setto” and “aBducted chest”) than in the two aDducted (nonbreathy) phonation types (“aDducted falsetto” and “aDducted chest”).

The main difference between the phonations in the two different registers (falsetto and chest) is seen in larger vertical phase differences of vocal fold vibra-tion, a prevalence of mucosal waves, and the duration of the closed phase. The observed values differed from individual to individual. In some cases, there was an overlap of closed quotient values for aBducted chest and aDducted falsetto. In aBducted chest, the effect of the vocal fold bulging caused by contraction of the thyroarytenoid muscle in chest register can be counter-acted by a decreasing adduction in the posterior glottis, allowing for a “breathy chest” phonation. The resulting glottal configuration is, in its extreme case, comparable to the one observed in hyperfunctional breathy voice or

TABLE 1. Four distinct phonation types, as created by dif-ferent degrees of cartilaginous adduction and membranous medialization.

Cartilaginous Membranous Voice quality adduction medialization

aBducted falsetto — —aDducted falsetto ++ —aBducted chest — ++aDducted chest ++ ++

muscle tension dysphonia.18 On the other hand, falsetto register (where the thyroarytenoid muscle is relaxed) can be produced with full closure of the posterior glottis, such as in the mid and upper range of trained female classical singing, and in countertenor singing.

The timbral effect of variations of the closed phase can be observed in the spectra shown in the bottom of Figure 3. When going from aBducted falsetto to 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 phonations with more adduction of the cartilaginous or membranous glottis (i.e., a “heavier registration”).19

TWO TYPES OF ADDUCTION— A PEDAGOGIC MODEL

Since cartilaginous adduction and membranous medial-ization can be controlled separately by both trained and untrained singers, these two physiological parameters can be displayed in a two dimensional plane in order to create a pedagogic model for sound quality adjust-ments made on the laryngeal level (Figure 4). This model consists of four quadrants, representing the four sound qualities described above. Different singing styles can be mapped onto the model, showing their main mechanism of production, such as:20

aBducted falsetto: e.g., untrained female singing (high tessitura), “naïve” male falsetto, “lighter” registration (both male and female) in pop and jazz;aDducted falsetto: e.g., trained female classical (high tessitura), countertenor;aBducted chest: e.g., untrained naïve singing (lower range), “lighter” registration (both male and female) in pop and jazz (low tessitura);aDducted chest: e.g., trained male classical, belting, rock, soul.The model is in no way restricted to the production of

four distinct phonation types. On the contrary, gradual adjustments along the two major axes (cartilaginous adduction and membranous medialization) are pos-sible. These fine controlled muscular adjustments allow experienced singers to create a large variety of sound timbres at the glottal level, increasing their expressional freedom within the aesthetic boundary conditions of their chosen singing style. Also, the model can provide

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pedagogic strategies, suggesting physiological adjust-ments to successfully create desired singing styles.

A MODEL CASE FROM THE SINGING STUDIO

A typical example for the application of the model described here would be the mid-range of female clas-

sical singers. We postulate that in classical singing (as opposed to other singing styles, such as belting) the desired quality above the primo passaggio (around pitch D4, ca. 295 Hz) would have to be aDducted falsetto,21

since (a) chest phonation is usually restricted to the lower range; and (b) breathy phonation, created by aBducted falsetto, is outside the aesthetic boundaries.

Figure 3. Images and signals documenting the vocal fold vibration in the four phonation types: aBducted falsetto (FaB), aDducted falsetto (FaD), aBducted chest (CaB), aDducted chest (CaD). From top to bottom: [Row 1] pairs of videostroboscopic images at the phases of maximum vocal fold contact and maximum glottal opening. The arrows point at the position of the vocal processes of the arytenoid cartilages, which are slightly set apart in FaB and CaB and close together in FaD and CaD; [Row 2] typical videokymographic images at the place of maximal vibration amplitude of the vocal folds; [Row 3] typical EGG signals (dark gray) and their first derivative, dEGG (light gray), for all phonation types, normalized both in amplitude and time. The x-axis represents normalized glottal cycle duration, and the y-axis shows EGG and dEGG signal amplitude, locally normalized per glottal cycle; [Row 4] spectrogram of sustained notes (taken from the audio channel of the videokymographic recordings) produced with phonation types A, B, C, and D consecutively. (Reprint from Christian T. Herbst, Sten Ternström, and Jan G. Švec, “Investigation of Four Distinct Glottal Configurations in Classical Singing—A Pilot Study,” Journal of the Acoustical Society of America 125, no. 3 [March 2009]: EL104–EL109, used with permission.) Acoustic and video files documenting the four phonation types can be freely obtained from http://dx.doi.org/10.1121/1.3057860.

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Untrained female singers have a tendency to produce sounds above the primo passaggio in either aDducted chest register, or in aBducted falsetto. In other words, they either “push” the chest register up (usually at the risk of an abrupt register transition at the upper end of the chest register range), or they produce soft breathy sounds, in both cases severely limiting the dynamic range and timbral variability of the voice at those par-ticular pitches.

The difficulty of switching from aDducted chest to aDducted falsetto can be explained physiologically. When changing from chest to falsetto register, the TA muscle relaxes and thus the membranous medialization is reduced. The resulting decrease of overall vocal fold adduction could be counteracted by a slight increase of cartilaginous adduction via the LCA and IA muscles, in order to keep the timbral change at a minimum. Such a maneuver (decreasing TA while increasing LCA and IA activity, respectively) is, however, both ambivalent and complex. Since the three involved muscles are all inner-vated by the recurrent laryngeal nerve, the required level of fine control might be hard to reach by some singers.

A valid pedagogic strategy would try to establish the aDducted falsetto at higher pitches (around B ♭

4 to F5), via calling (but not shouting) at vowel /u/, or using “pri-mal sounds.”21 This sound quality could then be applied to other vowels, and to pitches all the way down to the primo passaggio. When attempting to achieve a successful transition from (aDducted) chest to aDducted falsetto on ascending scales, there is the danger that the singer “gets stuck” in the chest register. In order to avoid this, it is advisable that ascending scales are sung only when: (1) the student reliably succeeded in producing aDducted falsetto in the primo passaggio on descending scales; and (2) she managed the falsetto-chest register transition at the primo passaggio without abrupt timbral changes.

CONCLUSION

The singing voice timbre can be controlled at the laryn-geal sound source by two types of glottal adduction: cartilaginous adduction (via the voice quality along the dimension of “breathy” vs. “pressed”) and membranous medialization (via the choice of register, that is, chest vs. falsetto). Both trained singers and nonsingers of both sexes can separately control these two physiological parameters. Cartilaginous adduction and membranous medialization can be mapped onto a two-dimensional plane in order to create a pedagogic model for sound quality adjustments made on the laryngeal level. This model may help to better understand different singing styles, and may be applied in the voice studio. The sug-gested model allows both singing teachers and voice therapists to better understand and diagnose their cli-ents’ voice production habits on a physiological level. This could eventually lead to novel pedagogic methods (or to better understanding and applying existing ones), thus increasing the efficiency and effectiveness of teach-ing and therapy.

ACKNOWLEDGEMENTS

The research has been supported in the Czech Repub lic by the European Social Fund Projects OP VK CZ.1.07/ 2.3.00/20.0057, and CZ.1.07/2.3.00/30.0004 “POST-UP,” and in Austria by the ERC Advanced Grant SOMACCA. We thank Dr. Ingo R. Titze for his helpful suggestions and comments on the manuscript.

Figure 4. Relationship between the two types of adduction and the four phonation types described here. This pedagogic model is not limited to distinct and extreme phonation types; rather, it encourages gradual, fine controlled adjustments along the two major dimensions, in order to increase the singer’s timbral variability for enhanced artistic expression.

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NOTES 1. David M. Howard and Damian T. Murphy, Voice Science,

Acoustics, and Recording (San Diego, CA: Plural Publishing, 2007), 33.

2. Peter Ladefoged, A Course in Phonetics, vol. 4 (Orlando, FL: Harcourt, 2001), 193–216.

3. Johan Sundberg, “The Acoustics of the Singing Voice,” Scientific American 236 (March 1977): 82–91; Donald G. Miller, Resonance in Singing (Princeton, NJ: Inside View Press, 2008), 187–206; Berton Coffin, Coffin’s Overtones of Bel Canto (Metuchen, NJ: The Scarecrow Press, 1980); Matthias Echternach, Johan Sundberg, Tobias Baumann, Michael Markl, and Bernhard Richter, “Vocal Tract Area Functions and Formant Frequencies in Opera Tenors’ Modal and Falsetto Registers,” Journal of the Acoustical Society of America 129, no. 6 (June 2011): 3955–3963; Elodie Joliveau, John Smith, and Joe Wolfe, “Acoustics: Tuning of Vocal Tract Resonance by Sopranos,” Nature 427, no. 6970 (January 2004): 116; Brad Story, “Vowel Acoustics for Speaking and Singing,” Acta Acustica united with Acoustica 90 (July/August 2004): 629–640; Johan Sundberg and Jörgen Skoog, “Dependence of Jaw Opening on Pitch and Vowel in Singers,” Journal of Voice 11, no. 3 (September 1997): 301–306; Johan Sundberg, “Articulatory Interpretation of The ‘Singing Formant’,” Journal of the Acoustical Society of America 55, no. 4 (April 1974): 838–844.

4. Johan Sundberg, “The Voice as a Sound Generator,” in J. Sundberg et al., Research Aspects on Singing (Stockholm: Royal Swedish Academy of Music, 1981), 6–14.

5. Ingo R. Titze, Principles of Voice Production, Second Printing (Salt Lake City: National Center for Voice and Speech, 2000), 281–305. To keep this manuscript concise, this discussion is limited to the two main registers: falsetto and chest. While vocal fry and whistle register are recognized as singing voice registers in their own right, they can only be produced at the extreme ends of the human fundamental frequency range and are less often employed during singing performance.

6. Titze, 17; Minoru Hirano, “Morphological Structure of the Vocal Cord as a Vibrator and Its Variations,” Folia Phoniatrica 26, no. 2 (1974): 89–94.

7. Willard R. Zemlin, Speech and Hearing Science—Anatomy and Physiology, 4th ed. (Boston: Allyn and Bacon, 1998), 104–119.

8. 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.

9. Titze, 126.

10. James L.Flanagan, “Some Properties of the Glottal Sound Source,” Journal of Speech and Hearing Research 1 (June 1958): 99–116.

11. During phonation, a minor, supplementary role in arytenoid adduction/abduction is played also by the thyroarytenoid (TA) and cricothyroid (CT) muscles; for details see Zemlin, 126–135.

12. Herbst et al.13. Maria Södersten, Stellan Hertegard, and Britta Hammarberg,

“Glottal Closure, Transglottal Airflow, and Voice Quality in Healthy Middle-Aged Women,” Journal of Voice 9, no. 2 (June 1995): 182–197.

14. The phase where air flow reached a minimum during a glottal cycle is sometimes called the “closed phase,” regardless of the actual occurrence of glottal closure.

15. Herbst et al.16. Herbst et al.; Christian T. Herbst, David M. Howard, and Jan

G. Švec, “The Sound Source in Singing—Basic Principles and Muscular Adjustments for Fine-Tuning Vocal Timbre,” in G. Welch, D. M. Howard, and J. Nix, eds., The Oxford Handbook of Singing (Oxford, UK: Oxford University Press, in print).

17. In a previously conducted pilot study, these sound qualities were labelled “naïve falsetto” (aBducted falsetto), “counter-tenor falsetto” (aDducted falsetto), “lyrical chest” (aBducted chest), and “full chest” (aDducted chest); see Note 19.

18. Murray Morrison, Linda A. Rammage, Gilles M. Belisle, C. Bruce Pullan, and Hamish Nichol, “Muscular Tension Dysphonia,” Journal of Otolaryngology 12, no. 5 (October 1983): 302–306.

19. Christian T. Herbst, Sten Ternström, and Jan G. Švec, “Investigation of Four Distinct Glottal Configurations in Classical Singing—A Pilot Study,” Journal of the Acoustical Society of America 125, no. 3 (March 2009): EL104-EL09.

20. This is a nonexhaustive list, intended solely to provide some basic orientation. Please note that some of the singing styles could also make use of other phonation types.

21. We readily acknowledge that many pedagogues use the term “head” or “mixed head” for the range immediately above the primo passaggio in classical female singing. However, in order to maintain the simplicity of the model proposed here, the latter is limited to the two registers chest and fal-setto, which can easily be distinguished from each other by measuring the closed or contact quotient. Please note that the proposed model allows for gradual changes is muscle activity, thus allowing for a “mixed register.” For an in-depth discussion of the mixed register of “voix mixte,” see Janice Chapman, Singing and Teaching Singing. A Holistic

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Approach to Classical Voice (San Diego, Oxford, Brisbane: Plural Publishing, 2006), 1–22.

Christian T. Herbst, born 1970, earned a master’s degree in classical voice pedagogy from the Mozarteum University, Salzburg, Austria. During his career as voice pedagogue (Tölzer Knabenchor, among others), Christian took interest in the physics and physiology of the voice. After a one year stay as visiting researcher at the Center for Computer Research in Music and Acoustics (CCRMA), Stanford University, he decided to put voice science as his future professional focus. He received his PhD in biophysics from the Department of Biophysics, University of Olomouc, Czech Republic, under the supervision of Dr. Jan Švec. From 2009 to 2013, Christian worked at the Department of Cognitive Biology, University of Vienna. He currently holds a position as postdoctoral researcher at the Department of Biophysics (Jan Švec group), University of Olomouc. He is an editorial board member of Logopedics, Phoniatrics and Vocology, and resident editor of the Journal of Voice.

Christian has published several prize-winning papers on laryngeal con-figurations in singing and on electroglottography (EGG), a noninvasive technique to gather physiological information of laryngeal dynamics during vocalization. He has invented the phasegram, a new method to

visualize chaotic phenomena in nonlinear systems, and EGG wavegrams, a technique for visualizing and analyzing vocal fold vibration properties. At the Laboratory of Bio-Acoustics at the University of Vienna he has created a setup for excised larynx experiments. The gathered data are used to perform cross-species comparisons of physical sound production mecha-nisms in mammals. In this context Christian recently published a paper about the low frequency physical sound production mechanisms in African elephants in the prestigious Science journal. www.christian-herbst.org

Jan G. Švec, PhD is an internationally renowned Czech physicist per-forming basic research on production of human voice. He has worked as a research scientist at the Center for Communication Disorders (Medical Healthcom) in Prague, the Czech Republic, at the National Center for Voice and Speech in Denver, CO, USA, and at the University of Groningen, the Netherlands. Currently he is at the Palacky University Olomouc, the Czech Republic, and serves also as an associate research scientist at the Voice Centre Prague. He designed videokymography, the method for high-speed visualization of vocal fold vibrations, which is used for advanced diagnosis of voice disorders. He collaborates with numerous research teams across the world and lectures world wide. From 2004 to 2011 he served as the chairman of the Voice Committee of the International Association of Logopedics and Phoniatrics (IALP).

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