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2018 Glottal Cycle of Open and Closed Head Voice Vowels Sung by Classically Trained Male Singers Bailey Rosenbalm

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SINGERS

THE FLORIDA STATE UNIVERSITY

College of Communication and Information

GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY

CLASSICALLY TRAINED MALE SINGERS

BAILEY ROSENBALM A Thesis submitted to the Department of Communication Science and Disorders in partial fulfillment of the requirements for graduation with Honors in the Major

Bachelor of Science: Spring, 2018

GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 2

The members of the Defense Committee approve the thesis of Bailey Rosenbalm defended on Friday, April 13th, 2018. Signatures on file with the Honors Program office.

______Dr. Richard Morris Thesis Director

______Dr. David Okerlund Outside Committee Member

______Dr. Shonda Bernadin Committee Member

GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 3

Abstract

The purpose of this research project is to use CQEGG and FFT spectra to examine the effects of /i/ on // in the head register of male singers. Examination was made using CQEGG and

FFT spectra. Hypotheses included; the initial // vowels having shorter closed quotients than the vowels that occurred after the /i/ vowels and the harmonic amplitude of H1, H2, H3, H4, H5, H6, and H7 in the region of formant one and two (F1, F2) of the initial vowel being lower than that for the // vowels that were followed by a /i/ vowel. Results include initial // vowels and those following the /i/ vowels having consistent closed quotients and the harmonic amplitudes (H1-H7) in the region of formant one and two being lower for the initial // vowel than the // vowels surrounded by /i/ vowels. Overall, sound energy was more focused in the regions of H3 and H6.

These alternating vowel exercises across the secondo passaggio allowed the singers to focus sound energy and employ resonant voice, a target vocal production for many vocal professionals.

GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 4

Introduction

Resonant voice is a target production in vocal training (Titze, 2001). For a singer to sing in resonant voice there needs to be a specified mix of laryngeal adjustment, vocal tract resonance and glottal closure. This mix of characteristics lends itself to vibrancy and ease (Titze, 2001).

Vibrancy being vocal strength and harmonic content, while ease is the lack of strain and tension in the vocal folds. Not only this, but singers derive a variety of benefits when using resonant voice. These benefits include; sound level remains strong, the voice sounds less pressed and breathy, and the vocal health of the singer remains intact (Titze, 2001). However, little is known about the relationship between the muscular adjustments of the vocal folds, the vocal tract’s properties related to physics, and the acoustic events that occur. With more knowledge about their relationship, new methods of effective instruction could be created. Resonant voice production is important when speaking specifically about differences in adjustments made by classically trained singers when they sing in different registers. With greater understanding of the acoustic phenomenon of resonant voice and how it is produced in different singing registers, there comes a larger and more effective gamut of not only research methods, but instructional methods as well.

Falsetto is the register of voice in which there is a strong cricothyroid dominance, less harmonic content, and a presence of breathiness due to the lack of closure of the vocal folds

(Henrich et al., 2011). The use of the term falsetto is slightly erroneous as it means “false voice” in Italian. Classically trained professional singers and voice instructors prefer the use of resonant voice while singing. Falsetto does not accomplish this and is not the preferred register to use

(Henrich et al., 2001). Head voice is the preferred register to use when seeking high sound level as it has higher harmonic content with almost no presence of breathiness. Henrich et al. (2011) GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 5 noted that resonance tuning is a strategy that may be employed to keep harmonic content and sound level high with minimal damage to vocal health and little strain or tension on the vocal folds. These authors stated that the singer makes adjustments to jaw height, pharyngeal space, laryngeal height, tongue position, and lip position so that a resonance frequency of the vocal tract is tuned to match a harmonic frequency from the glottal source signal. By adjusting the vocal tract resonance so that a resonance frequency and harmonic occur close together, the singer creates a sound in which a frequency is strongly resonated and has greater amplitude. The frequency that is resonated strongly depends on the resonance tuning strategy that is employed.

Henrich et al. (2011) also noted, sopranos and altos employ resonance tuning in upper parts of their ranges coupling resonance frequency one with the first harmonic, specifically this can begin in the secondo passaggio. Classically trained soloists use this strategy to tune their voices in order to project over the large orchestras they are frequently accompanied by. These authors confirmed that classically trained tenors use coupling of resonance frequency two and harmonic three in a portion of their range to support a higher sound level. More importantly, the singers also adjust resonance so that formants three and four are close together within 2500-3000 Hertz

(Henrich et al., 2011).

Another note is that singers apply habits of laryngeal and vocal tract adjustments, that originate from speech, into their singing (Bozeman, 2008). These adjustments may inhibit the vibrator and resonator from making the proper adjustments in the more extreme registers of the voice; for instance, the zono di passaggio. Thus, singers must learn how to differentiate the strategies used in speech from those used in singing (Bozeman, 2008). This is related to the zono di passaggio as it is the range of the singing voice in which the muscles of the larynx shift to create the head register sound; making it vital to take into consideration when coaching male GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 6 singers on maneuvering in and around their secondo passaggio to keep sound level and resonance high as they are transitioning into the highest portion of their range with the most thyroarytenoid activation (McCoy, 2004).

Sound is introduced at the glottis and resonates through the vocal tract and out of the mouth. Titze (2001) discussed the inertive properties of the vocal tract and how they are related to resonant voice. Inertance is the physical property of an air mass being accelerated or decelerated. Titze (2001) said that the inertive properties of the vocal tract feed energy back to the sound source and strengthen the harmonic content of the glottal signal, allowing more efficient vocal fold vibration. In an inertive vocal tract the supraglottal pressure pushing the air column is in phase with the velocity of vocal fold oscillation. He continued by saying that supraglottal pressure and rate of change of airflow are both positive during glottal opening, raising the pressure through the glottis and pushing the vocal folds apart. During glottal closure, rate of change of air flow and supraglottal pressure are both negative, lowering the pressure through the glottis and pulling the vocal folds together. These aerodynamic and tissue interactions assist the vocal folds in oscillation. Titze (2001) stated the general definition of compliance as the changing of volume when force is applied, in the case of singing, to the air in the glottis. In a compliant vocal tract, the supraglottal pressure is not in phase with the velocity of vocal fold oscillation. The supraglottal pressure during opening is always less than during closing. This rising pressure during the open phase of oscillation creates a push but no pull. A compliant vocal tract does not lend itself to efficient vocal fold vibration. This usually causes a shift to falsetto upon entering the secondo passaggio along with lowering the sound level and leading the singer to use an unhealthy method to increase sound level upon entering the register.

Thus he made a contrast between the use of an inertive vocal tract and that of a more compliant GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 7 one. Using a compliant vocal tract is inefficient, therefore allowing the vocal tract to be as inertive as possible is vital (Titze, 2001).

Titze (2001) observed a high frequency dependent inertance pattern with an open mouth model; he said that the inertance is enhanced when the epilarynx is narrowed. With inertance increased at higher frequencies, the singer’s formant can be produced. The presence of the singer’s formant adds ring to vocal quality. Ring is the resonant, trumpet-like overtones most commonly heard in the voices of operatic singers (Sundberg, 1987). His findings include the need to lower and narrow the epilarynx when singing at higher frequencies. However, narrowing the epilarynx is not a widely accepted practice in vocal training (Titze, 2001). Burk et al. (2017) also brings up the use of epilaryngeal narrowing. They found that the narrowing of the epilarynx made it hard for transoral endoscopy cameras to capture the vocal folds in motion. To investigate the vocal fold patterns in the secondo passaggio they used transnasal endoscopes to observe epilaryngeal adjustment. They observed epilaryngeal narrowing and concluded that it was unlikely to be caused by the endoscope (Burk et al., 2017). However, narrowing the epilarynx may cause strain and tension that many voice instructors are trying to avoid. Therefore, the conclusions of both of these works of research bring to light a disconnect between how scientists understand the physical adjustments of the vocal tract related to target vocal production and how voice instructors and classically trained singers understand them. These methods, when put into practice, may not be as effective as researchers think. There lies a prime example that supports the need for the efficacy of instructional methods to be more thoroughly researched.

Timbre is the distinguishable characteristics of the voice. This concept is related to vowel modification. There is a timbral shift that occurs upon entering the secondo passaggio that is characterized by specific acoustic events. For most men, register shifts occur when the third and GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 8 fourth harmonic (H3, H4) passes over the second formant (F2). Register shifts are the result of this acoustic phenomenon because if it were a matter of laryngeal adjustment; all vowels would turn over at the same frequency but, they do not (Henrich et al., 2011). Register shifts occur about one octave below the first formant for each vowel, some vowel shifts may go unnoticed because their frequency is below the zono di passaggio (Bozeman, 2010). Knowledge of these register shifts can be essential to creating strategies for training. Singers can accelerate register shifts by lowering F1which is accomplished by lowering the larynx, widening the pharynx, and rounding the lips. The challenge in this being that training in secondo passaggio requires the vocal tract to remain stable while engaging the muscles necessary to lower F1. Bozeman (2010) found that keeping the tube shape the same while increasing pitch near the secondo passaggio will affect the integrity of the vowel. Maintaining tube shape may cause an // vowel to sound comparable to a /i/ vowel. Therefore, vocal exercises should (1) aim to open the vowel until after turning over and (2) use vowel substitutions in foresight of vowel modification after turning over, to keep the larynx stable (Bozeman, 2010).

Echternach and Richter (2012) highlighted the point that a goal of classical singing is to hide register shifts. These authors stated that to successfully hide register shifts, vocal fold oscillation should remain stable during register shifts. However, one interesting feature of the male singing voice found by Echternach and Richter is that during head voice the oscillatory patterns are similar to those in chest voice and third harmonic dominance is present in both registers (Echternach & Richter, 2012). Based on this fact, these authors conclude that exercises employing stable vocal functions are important for singing in falsetto, but not necessarily head voice because oscillatory patterns are already stable relative to chest voice.

In addition, Echternach, Burk, Koberlein, Herbst, Dollinger, and Richter (2017a) GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 9 measured the subglottic pressure and open quotient values of classically trained tenor singers when they sang a pitch glide form A3 to A4 on an /i/ vowel. They hypothesized that the open quotient values will remain stable during a transition from modal to stage voice above the passaggio and increase during a transition from modal to falsetto. The modal to falsetto transition would be considered a speaking voice transition that did not incorporate the singers’ training that was incorporated when the singers’ used their stage voice. The results of their study indicated that the open quotient values did change some (an increase during the passaggio) during the glide from modal to stage voice above the secondo passaggio, but remained stable overall with values consistently lower than those for the glide from modal to falsetto (Echternach et al., 2017a). Echternach, Burk, Köberlein, Burdumy Döllinger, and Richter (2017b) also studied the sample entropy level across the three corner vowels (/a/, /i/, and /u/). Results of the study included the finding that open quotient values for /a/ in a glide from modal to stage voice above the secondo passaggio exhibited no major differences, indicating stability in the /a/ vowel when the singers used their training during the passaggio. It should also be noted that in this study major compressions of the epilaryngeal tube in the vocal tract were observed for the open vowel (Echternach et al., 2017b).

In addition, Echternach, Richter, and Traser (2014) used MRIs to investigate the extent that vocal tract adjustments occurred during register transition. They observed vocal tract modification during register transition that varied across the singers. During production of vowels with high first formant frequencies the singers’ lips and jaw were opened more than when compared to vowels with lower frequency first formants. Register transitions to head voice were accompanied by minimal changes in the size of lip and jaw opening. Also, the tongue dorsum experienced no adjustment during this register transition and these singers increased their GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 10 pharynx width during the secondo passaggio (Echternach et al., 2014). The singers exhibited a variety of vowel modifications during their register transitions that sometimes varied by vowel. It is clear that more research ought to be done in this area of voice to confirm the presence or absence of patterns of vocal tract modification.

Another method of investigation was used my Bernadin, Ellerbe, Kessela, Okerlund, and

Morris (2014) in exploring the features of the primo passaggio of trained female singers.

Electroglottographic (EGG) measures were used to reveal information about closing quotients during vowel production. Multiple source patterns were evaluated for reliable closing quotient measurements using an algorithm. They used audio and EGG signals to measure closing quotient values via derivatives of the signals. The derivative of the EGG (dEGG) and EGG signals were used to mark vocal fold closure and the derivative of the audio (dAudio) and EGG signals were used to mark vocal fold opening. Using subjects with varying levels of training allowed them to test the measurement system across an array of signals and ensure the reliability of the method.

Results of the study indicated that the use of EGG signals is a reliable method of collecting information about closed quotients (CQEGG). More research needs to be done to test the reliability of these algorithms and to provide stronger support for using these source parameters in voice research (Bernadin et al. 2014).

Purpose

Transitioning from /i/ vowels to more open vowels has been a long standing practice for vocal pedagogues to address the differences in glottal activity and aerodynamic efficiency across these vowels when classically trained singers sing in their head voice. The purpose of this research project is to use CQEGG and FFT spectra to examine the effects of /i/ on // in the head register of male singers. Examination was made using CQEGG and FFT spectra. Hypotheses GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 11 included: the initial // vowels having shorter closed quotients than the vowels that occurred after the /i/ vowels and the harmonic amplitude of H1, H2, H3, H4, H5, H6, and H7 in the region of formant one and two (F1, F2) of the initial vowel being lower than that for the // vowels that were followed by a /i/ vowel.

Methods

Participants

Thirteen classically trained male singers with varying degrees of experience and education served as participants. Before participating the singers had to demonstrate the ability to move into head voice through the secondo passaggio and ensure they were of good vocal health.

Eight of the participants were undergraduate students, four were graduate students, and one was a professional singer. The students were enrolled as vocal performant majors at Florida State

University and all participants had at least four years of experience. The study was approved by the Florida State University Human Subjects Committee on 12 January 2017. The approval number is HSC#2016.20015 for the study.

Procedures

When each participant arrived for the experimental session he first completed a set of vocal warm ups. Upon completion, an omnidirectional condenser microphone was placed in front of him with the microphone eighteen centimeters away from the mouth. Singers were instructed to sing the /:i::i:/ sequence at an A4 or 440 Hertz. This signal was amplified and sent to an MAudio Mobilepre USB amplifier and recorded on the second channel of a wav. file using Audacity software (version 2.1.3). During exercises, each participant’s vocal fold contact area was recorded using a Glottal Enterprise EGG (ECM-100). The EGG electrodes were placed GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 12 on the participants’ neck over the lamina of the thyroid cartilage and secured with a Velcro strap.

The recorded signals were saved as wav. files and then viewed via the Audacity software.

Data Measurement

The amplitude maxima and minima of the vibrato phased for each vowel were determined and the times for each of these recorded using the spectrum routine of the Pratt acoustic software (version 6.0.29). These moments in the recorded signals were used for making data measurements. The CQEGG values were determined using a MatLab algorithm and recorded in a spreadsheet. The MatLab algorithm required the experimenter to mark the moment of the beginning of vocal fold closure from the dEGG signal, the moment of vocal fold opening from the dAUDIO signal, and the beginning and ending points of the cycle from either signal. The amplitude of the first seven harmonics at each measurement point were determined using the spectrum routine of Praat and recorded in the spreadsheet.

Analysis

The data was analyzed using a repeated measure analysis of variance with the CQEGG and the amplitudes of H1, H2, H3, H4, H5, H6, and H7 as the dependent variables and vibrato phase, and vowel as independent variables.

Inter-observer reliability was determined by having the investigator remeasuring 20 percent of the data and comparing the two sets of measurements via a t-test and correlations statistics. Similarly, a second investigator measured 20 percent of the data and compare these measurements to the original ones via a t-test and correlations statistics.

Results GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 13

The harmonic amplitude and CQ data exhibited differing patterns. The harmonic amplitude means varied across the vowels with small standard deviations, whereas the CQ means remained more consistent, but the data indicated greater standard deviations.

Analysis of the harmonic amplitude data measured at the vibrato peaks and troughs over five glottal cycles for the three vowels repetitions revealed the following. Significant main effects occurred for the harmonics (F(6,18)=3.709, p<0.05, p2=0.553). Interaction effects occurred for the harmonics across the three vowel repetitions (F(12,36)=3.723, p<0.05,

p2=0.554), for the harmonics across the three vowel repetitions and the five measured glottal cycles (F(48,144)=1.370, p<0.05, p2=0.313), and for the vibrato cycles across the three vowel repetitions and five measured glottal cycles (F(8,24)=2.244, p<0.05p2=0.428). In contrast, analysis of the closed quotient data revealed no significant differences or interactions.

50 Relative dB SPL Relative dB 45

40 1234567 Harmonic

Fig. 1: Mean amplitudes for the first seven harmonics in relative dB SPL across all vowels and participants.

Figure 1 illustrates that overall, across all vowels and cycles, third harmonic dominance was seen with increased singer’s formant presence. Harmonic three had the greatest mean amplitude value at 60.58 dB SPL with the amplitude of the surrounding harmonics (H1, H2, and

H4) being significantly lower. Harmonic six had a mean amplitude value of 57.25 dB SPL with GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 14 the surrounding harmonics (H5 and H7) being significantly lower. Standard error values include

1.557, 3.002, 0.954, 1.001, 3.562, 0.999, and 1.056 for harmonics one through seven, respectively. Thus, the variability of the data was higher for H2 and H5 than for the other harmonics.

Harmonic vowel interaction

Figure 2 shows the increase in the mean amplitude of H3 for the second and third productions of /a/ and the relative stability of the mean amplitudes across the vowel repetitions for the other harmonics. The statistical analysis illustrated harmonic amplitude for the initial vowel were lower than that for the // vowels that were preceded by a /i/ vowel (F(12,36)=3.723, p<0.05, p2=0.554). H3 had mean amplitude values that were above 57 dB for each vowel while all other harmonics had mean amplitude values at or below 57 dB.

1st Vowel Relative SPL Relative dB 45 2nd Vowel 3rd Vowel 40 012345678 Harmonic Fig. 2: Mean amplitudes of the harmonics for each of the three /a/ vowel productions across all participants.

The H1 through H7 mean amplitudes ranged between 49 and 57.1 dB SPL for the initial

// vowel. For the second and third // vowels, H1 through H7 mean amplitudes ranged between

50 and 62.35 dB SPL. For all three vowel productions H3 had the highest mean amplitudes. The mean amplitudes for H3 in the second and third // vowels were 62.4 and 62.3 dB SPL GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 15 respectively. H6 had the second highest mean amplitude values at 57.9 and 56.7 for vowels two and three. The productions were relatively consistent across the participants with standard errors values for H3 between .058 and 1.44 dB and standard error values for H6 between 0.77 and 1.42 dB.

Harmonic vowel cycle interaction

Figures 3a-c illustrate the observed interaction between the amplitudes of the harmonics and the vowel repetitions with the harmonics and the series of glottal cycles measured. Figure 3b and c show an increase in relative dB SPL during the second and third vowels with a range between 47 and 61 dB for the first vowel and ranges between 47 and 64 dB for the second and third vowels. Once again there is a statistically significant increase in the region of the singer’s formant (H6) for all three productions. Statistical analysis confirmed an increase in mean amplitude over the first three vowels for H3 and H6 (F(48,144)=1.370, p<0.05, p2=0.313).

70 65 60 55 50 Cycle 1 45 Cycle 2

Relative SPL Relative dB 40 Cycle 3 Cycle 4 35 Cycle 5 30 012345678 Harmonic Fig. 3a: Mean amplitudes in dB SPL for each glottal cycle during the production of the first // vowel across all participants.

GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 16

70 65 60 55 50 Cycle 1 45 Cycle 2

Relative SPL Relative dB 40 Cycle 3 Cycle 4 35 Cycle 5 30 012345678 Harmonic Fig. 3b: Mean amplitudes in dB SPL for each glottal cycle during the production of the second // vowel across all participants.

70 65 60 55 50 Cycle 1 45 Cycle 2

Relative SPL Relative dB 40 Cycle 3 Cycle 4 35 Cycle 5 30 012345678 Harmonic Fig. 3c: Mean amplitudes in dB SPL for each glottal cycle during the production of the third // vowel across all participants.

Not only did mean amplitude for H3 and H6 increase over time, but as the singers increased the focus of the // vowels the range across the cycles decreased which shows stabilization of the // vowel. The range of mean amplitudes for H3 mean spanned from 54.9 to

60.4 dB SPL for vowel one, from 59.9 to 63.8 dB SPL for vowel two, and from 61.1 to 62.0 dB

SPL for vowel three. The ranges between cycles for the mean harmonic amplitudes of H3 were

5.5 dB for vowel one, 1.8 dB for vowel two, and 0.9 dB for vowel three. The mean harmonic amplitudes of H6 for vowel one spanned from 54.3 to 59.3 dB SPL, from 56.4 to 59.5 dB SPL GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 17 for vowel two, and from 55.6 to 58.1 dB SPL for vowel three. The productions across cycles were relatively stable with standard error for H3 did not exceed 2.31 and did not exceed 2.26 for

H6.

Vibrato cycle, mean harmonic amplitude, and glottal cycle interaction

Figure 4a-c illustrate the observed interactions between the harmonic amplitudes and the vibrato peaks and troughs for the glottal cycles of the three // vowel productions

(F(8,24)=2.244, p<0.05p2=0.428). As can be seen in figures 4a, 4b, and 4c mean amplitude differences between the vibrato peaks and troughs occur mainly in the first cycles measures on the first vowel. This stabilization is illustrated by the decreasing ranges between the peaks and troughs for cycles one and two across all three vowels and that the vowel three peak and trough measures for all cycles were closest in range when compared to the first two // vowels. These data resulted in a significant difference among the glottal cycles and the vibrato peaks and troughs.

Relative dB SPL Relative dB Vibrato Peak 45 Vibrato Trough 40 0123456 Glottal Cycle

Fig. 4a: Mean harmonic amplitudes at vibrato peaks and troughs for // vowel one across all harmonics and participants.

GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 18

Relative SPL Relative dB Vibrato Peak 45 Vibrato Trough

40 0123456 Glottal Cycle Fig. 4b: Mean harmonic amplitudes at vibrato peaks and troughs for // vowel two across all harmonics and participants.

Vibrato Peak Relative SPL Relative dB 45 Vibrato Trough

40 0123456 Glottal Cycle Fig. 4c: Mean harmonic amplitudes at vibrato peaks and troughs for // vowel three across all harmonics and participants.

The mean amplitudes for the vibrato peaks of the glottal cycles during the first vowel ranged between 53.0 and 54.1 dB SPL and the mean amplitudes for the vibrato troughs of the same cycles ranged between 53.3 and 56.0 dB SPL. For vowel two the mean harmonic amplitudes for the vibrato peaks ranged between 53.8 and 55.6 dB SPL and the mean harmonic amplitudes for the vibrato troughs ranged between 54.4 and 56.1 dB SPL. Finally, for vowel three the mean harmonic amplitudes for the vibrato peaks ranged between 53.3 and 55.6 dB SPL and the mean harmonic amplitudes for the vibrato troughs ranged between 54.1 and 55.9 dB GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 19

SPL. The singers exhibited good stability in these productions as the standard error did not exceed 1.21 dB for vowel one, 1.54 dB for vowel two, and 2.11 dB for vowel three.

Closed Quotient

Figure 5 illustrates the consistency between closed quotient values for vibrato peaks and troughs across the // vowels. The CQ values ranged from 74.0 to 76.2 with standard errors that ranged from 4.36 to 6.01. In contrast with the findings for the harmonic amplitudes there are no apparent or significant interactions between glottal cycle and vowel.

75 Peak 1 70 Trough 1 Peak 2 Trough 2 65 Closing Quotient EGGQuotient Closing Peak 3 Trough 3 60 0 1 2 3 4 Vowel

Fig. 5: Closed quotient values for vibrato peaks and troughs across the three // vowels across all harmonics and participants.

Discussion

The purpose of this study was to examine the effect of singing an /i/ vowel (closed vowel) on the singing of a following // vowel (open vowel) as sung by classically trained tenors using their head register. Hypotheses for the study included; that the initial // vowels would have shorter closed quotients than the vowels that occurred after the /i/ vowels and the amplitudes of H1, H2, H3, H4, H5, H6, and H7 in the region of formant one and two (F1, F2) of GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 20 the initial vowel would be higher for the // vowels that followed a /i/ vowel. Results did not support the first hypothesis however, they supported the second.

The first hypothesis was not supported by results that indicated no change in glottal cycle duration across vowels. The initial // vowels had consistent closed quotient values with the // vowels that occurred after the /i/ vowels. This finding is consistent with that reported by

Echternach and colleagues (Echternach & Richter, 2012; Echternach et al. 2017a; 2017b). These authors found similar CQ levels for the chest and head registers of classically trained tenors when the singers used their voice training during the passaggio. They stated that these well trained tenors exhibited stable vocal function above the passaggio for optimal stage performance. The findings of the present study are in agreement with the findings of the aforementioned studies. The CQ results from the singers in the present study had even less variation than those reported by Echternach et al. (2017a). This increase in glottal cycle consistency could be contributed to the coupling of the // and /i/ vowels after a pitch glide through the secondo passaggio.

The second hypothesis was supported by results that implied vocal tract interactions through the changes in harmonic amplitudes between the first and second formants of the three vowel repetitions. Harmonic amplitude changes were noted for the harmonics across the three vowel repetitions and the five measured glottal cycles, and for the vibrato cycles across the three vowel repetitions and five measured glottal cycles. There were increases of mean amplitude in

H3 and the region of the singer’s formant (H6), indicating that the singers increased the focus of the acoustic energy in these two frequency areas.

The H3 mean amplitude increased significantly between the first and second // vowels.

Thereafter, stabilization of mean amplitude across the vowels occurred. For the interaction GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 21 between the harmonics across the three vowel repetitions and the five measured glottal cycles we found an increase in relative dB SPL between the first and second vowels with relative dB SPL stabilizing after the second vowel. An increase in the region of the singer’s formant (H6) also occurred. Not only did the mean amplitudes of H3 and H6 at vowel two and three increase; but the range of values of the measures decreased, this indicated stabilization in the vowel. For the vibrato cycles across the three vowel repetitions and five measured glottal cycles another indication of stabilization occurred. It was found that the ranges between the peaks and troughs for cycles one and two decreased across all vowels. The peak and trough measures for vowel three were the closest in range in comparison to the first two // vowels. Previous data collected during a secondo passaggio transition and when shifting registers on a single note within the primo passaggio indicated that the harmonic amplitudes during vibrato peaks were greater than those during passaggio troughs in females (Morris, Okerlund, & Craven, 2016; Morris,

Okerlund, & Farr, 2016). The difference between the results of the current study and the previous findings illustrates the effect of the /i/ vowel in the exercise; when producing a /i/ and // vowel so closely together the singers maintained the increased resonance and focus of the /i/ vowel during the // vowel production. The results of this study indicate that coupling an // and /i/ vowel in a vocalese is an effective vocal exercise for improving // vowel vocal resonance.

As noted by Titze (2001), singers must employ a mix of laryngeal adjustments, vocal tract resonance, and glottal closure to sing in classically trained manner. The laryngeal adjustment being achieved by alternating // and /i/ vowels; the vocal tract resonance being the coupling of H2 and H3 and the increased mean amplitude of H3 and the region of the singer’s formant (H6); and the glottal closure being the consistent glottal cycle duration across vowels. GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 22

Titze (2001) also found a high frequency dependence pattern with an open mouth model which was enhanced when the epilarynx was narrowed however, epilarynx narrowing isn’t a widely accepted strategy in classical singing as it causes tension. During the // vowel the epilarynx is more narrowed than when compared to the /i/ vowel. Pairing these to vowels in the exercise slightly opens the narrowed epilarynx of the // vowel to allow for increased resonance and relative dB SPL. Echternach et al. (2017b) explored epilaryngeal constrictions of the vocal tract and concluded that because these constrictions were present in both transnasal and transoral laryngoscopy that they may be considered a physiological finding of professionally trained western classical tenors. So, it seems that there can be a healthy amount of epilaryngeal constriction seen during registration events in the secondo passaggio and that alternating between // and /i/ vowels can achieve this mix of constriction and openness.

Echternach, Richter, and Traser (2014) found that vowel conditions may affect vocal tract modifications caused by registration events. They also found that pharynx width increased during exercises performed in the secondo passaggio. The results from this study support these findings. When beginning the exercise, the singers displayed relatively unstable vocal tract resonances. After a registration event occurred and the singer moved from an // vowel to a /i/ one and back, stabilization occurred. Epilaryngeal characteristics of increased width from the /i/ vowel lingered during the // vowel allowing resonance to increase.

Limitations for the study included the lack of laryngoscopy. Viewing the vocal folds would have allowed observation of their oscillatory patterns. Such data would have enhanced what could be said about the laryngeal behaviors in this study. In addition, more classically trained singers need to be observed to determine if the patterns of vocal tract and laryngeal adjustments reported in this study can be generalized across classically trained singers. GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 23

Future research should be done to further explore the effect of // and /i/ vowels on vocal exercises in chest, mixed, and head registers as well as through the passaggio for classically trained male and female singers. It would be beneficial to include visual perceptual data from laryngoscopy and high speed video to apply similar research questions to a number of different vowel conditions across registers. Not only could the continued exploration of the interactions between the physical and acoustic properties of the vocal tract expand our understanding of this topic in voice, but also pave the way for new and effective practices for achieving resonant voice in Western classical singing.

GLOTTAL CYCLE OF OPEN // AND CLOSED /i/ HEAD VOICE VOWELS SUNG BY CLASSICALLY TRAINED MALE SINGERS 24

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