The Effect of Traditional Singing Warm-Up Versus Semioccluded Vocal Tract Exercises on the Acoustic Parameters of Singing Voice *Emily Duke, †Laura W. Plexico, †Mary J. Sandage, and †Matthew Hoch, *Rockville, Maryland, yAuburn, Alabama Summary: Objectives/hypotheses. This study investigated the effect of traditional vocal warm-up versus semioccluded vocal tract exercises on the acoustic parameters of voice through three questions: does vocal warm-up condition significantly alter the singing power ratio of the singing voice? Is singing power ratio dependent upon vowel? Is perceived phonatory effort affected by warm-up condition? Hypotheses were that vocal warm-up would alter the singing power ratio, and that semioccluded vocal tract warm-up would affect the singing power ratio more than no warm-up or traditional warm-up, that singing power ratio would vary across vowel, and that perceived phonatory effort would vary with warm-up condition. Study design. This study was a within-participant repeated measures design with counterbalanced conditions. Methods. Thirteen male singers were recorded under three different conditions: no warm-up, traditional warm-up, and semioccluded vocal tract exercise warm-up. Recordings were made of these singers performing the Star Spangled Banner, and singing power ratio (SPR) was calculated from four vowels. Singers rated their perceived phonatory effort (PPE) singing the Star Spangled Banner after each warm-up condition. Results. Warm-up condition did not significantly affect SPR. SPR was significantly different for /i/ and /e/. PPE was not significantly different between warm-up conditions. Conclusions. The present study did not find significant differences in SPR between warm-up conditions. SPR differences for /i/, support previous findings. PPE did not differ significantly across warm-up condition despite the expectation that traditional or semioccluded warm-up would cause a decrease. Key Words: Vocal warm-up–Semioccluded vocal tract–Singing power ratio.

INTRODUCTION Literature describing singing warm-up tasks offers a variety of exercises with, at times, conflicting data.1–3 Approaches to singing warm-up vary widely with different vocal warm-up exercises perceived as being useful for different purposes. Traditionally, vocal warm-up approaches for singing have ranged from whole body approaches4–6 to targeted warm-up for the laryngeal source and vocal tract tuning.7–9 Historically, many singing voice warm-up exercises have targeted laryngeal source function to train a smooth transition between vocal registers.4,5 Humming, or sustained nasal consonants, is a common warm-up component.5–8,10 Humming can be a voice building technique allowing for a clear tone and flow phonation with the least amount of effort from the singer.8 Humming also ‘‘brings the voice forward on the vocal mask’’ (p. 32).6 Other warm-up exercises expand the functional frequency range through use of ascending and descending scales, arpeggios, and glissandi.5,7 Traditionally, singing warm-up protocols have also addressed relaxation of the lower jaw muscles.5,7 Also recommended are vocal warm-up exercises that focus on vocal tract tuning, or filter effects in conjunction with phonation. Vocal exercises that target resonance balancing are important for developing clean on-glides and off-glides in sung

Accepted for publication December 19, 2014. From the *Language & Voice Experience, Rockville, Maryland; and the yAuburn University, Auburn, Alabama. Address correspondence and reprint requests to Laura Plexico, Auburn University, CCCSLP, 1219 Haley Center, AL 36849. E-mail: [email protected] Journal of Voice, Vol. -, No. -, pp. 1-6 0892-1997/$36.00 Ó 2015 The Voice Foundation http://dx.doi.org/10.1016/j.jvoice.2014.12.009

vowels.10 Balanced resonance is achieved by coupling the tone produced in the oral and nasal cavities in the vowels following any of the nasal consonants, /m/, /n/, or /s/.10 The use of nasal consonants and vowels in vocal warm-up is thought to improve overall vocal quality by training maximum vocal economy. Vocal economy has been defined as the maximized ratio between voice output and intraglottal impact stress,11 whereby voice output is maximized while intraglottal impact stress is minimized. More recently voice, scientists have focused on the merits of semioccluded vocal tract exercises as a distinct set of vocal warm-up maneuvers that enhance both vocal source and vocal tract filter function.12–17 Semioccluded vocal tract exercises are those that partially occlude the vocal tract causing decreased glottal resistance and increased glottal flow.18 Lip trills and tongue trills are common semiocclusives.19,20 The vocal tract narrowing associated with semioccluded vocal tasks increases supraglottal and intraglottal back pressures at the level of the glottis. These back pressures keep the vocal folds optimally separated and may provide impedance that allows for greater ease of phonation.16,21 Andrade et al12 examined various types of semioccluded vocal tract exercises. The exercises were divided into two types: single source exercises (eg, straw phonation and humming) and exercises with a secondary source of vibration (eg, lip trills and tongue trills). Tasks were evaluated for differences in contact quotient range (CQr) and F1  F0. CQr is a measure of variability of the open and closed phases, and F1  F0 represents the difference in hertz between the fundamental frequency and first formant. Results showed that single-source semioccluded vocal tract exercises were associated with lower CQr values (ie, steady closed quotient values) and lower F1  F0 values (indicating easier phonation), and that semioccluded

2 vocal tract exercises with a secondary source of vibration were associated with higher CQr values (ie, fluctuating closed quotient values) and higher F1  F0 values (indicating more effortful phonation). These results indicate that single source exercises like straw phonation promote easier phonation, whereas other semioccluded vocal tract exercises such as trills may make phonation more difficult while still having a positive effect on the larynx. Schwarz and Cielo22 supported these findings in that following semioccluded vocal exercise, acoustic measures as well as auditory perceptual measures of participants’ voices were found to be improved despite the participants’ report of a ‘‘negative’’ proprioceptive sensation. Thus, it is possible that a secondary source of vibration in a semioccluded exercise may improve vocal function while making the perception of phonation more difficult for the individual performing the exercise. Because easy phonation is one of the goals for singing, straw phonation may be preferable. There are four other advantages for use of a straw or tube instead of lip trills in semioccluded warm-up exercise. First, use of a tube causes pressure behind the lips to be three times greater than when phonating on /u/, which points to the tube providing more tissue vibration. This sensation is important for motor learning and may reinforce the behavior that creates the vibration of the facial tissue,11 which accompanies impedance matching between the glottis and vocal tract.23 Second, added vocal tract length achieved by use of a tube lowers the first formant and increases inertive reactance in the vocal tract.21 When reactance is high, average airflow is reduced, decreasing effort for phonation.24 Third, sound at the larynx is easier to monitor when using a tube as there is no added vibration at the lips.15 Fourth, tube diameter can be adjusted for the resistance needs of the individual, which is ideal for training.15 There is emerging evidence supporting the utility of semioccluded vocal tract exercises for increasing vocal economy and efficiency.16,25,26 According to models by Story et al21 partial occlusion of the vocal tract may provide impedance that allows for greater ease of phonation. Recent research has focused on the use of drinking straws to semiocclude the vocal tract.14,17,26 Single-subject studies have shown that phonation into a straw can cause changes in the vocal tract that remain after the straw is removed.11,13 The duration of such changes after straw phonation was not specified. Vampola et al15 observed that phonating into a glass tube resulted in a raised velum and an expanded cross-sectional vocal tract area. This expansion of the pharynx over the epilarynx is important for production of the singer’s formant, a phenomenon seen mainly in classically and operatically trained male singers.27–29 The singer’s formant can be defined as a strong area of resonance around 3000 Hz, whose resonant frequency can be as wide spread as 2600–4000 Hz.29 It is formed when two or more formants approach each other in frequency, the formant amplitudes increase, and the third, fourth, and fifth formants form a formant cluster.13,31 Studies by Laukkanen et al,26 Laukkanen et al,14 Guzman et al,13 and Vampola et al15 lend support to the theoretical models by Sundberg27 and Titze and Story31 regarding vocal tract configuration for clustering of formants, but the observed effects and external validity are limited as

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these studies investigated single subjects. A large pharynx opening relative to the epilarynx supports production of the singer’s formant,27 yet warm-up influences on the pharyngeal and epilaryngeal opening are not well understood. Indirectly, the singer’s formant can be derived acoustically by calculating the singing power ratio (SPR),32–34 which is the ratio of the highest peak between 2 kHz and 4 kHz and the highest peak between 0 kHz and 2 kHz.33 Omori et al33 observed power spectra from sung sustained /a/ phonation recordings of both trained and untrained male and female singers. SPR was calculated from the spectra, and experienced singing teachers rated the /a/ recordings on bipolar scales from 1–7 for ‘‘dull’’ to ‘‘ringing’’ and ‘‘thin’’ to ‘‘rich.’’ In both males and females, SPR was greater in singers than nonsingers. Perceptual ratings of ‘‘richness’’ had a significant correlation to SPR. This echoes previous findings that voices whose spectra featured a visually discerned singer’s formant had relatively high ‘‘resonance/ring’’ perceptual ratings from expert voice teachers.35 If upper frequency harmonics demonstrate more energy than lower frequency harmonics, as is the case when the singer’s formant is present, SPR will be relatively low.11 A reliable SPR is more likely to be observed in men than women because female singers have not been observed to produce a singer’s formant with the same reliability as male singers.29 It is difficult to identify the singer’s formant in high-pitched voices because harmonics in high frequencies are spaced widely apart making peaks more difficult to discern.30 Vocal warm-up is considered essential to most singers and voice teachers.2 It is believed that voice use in speech and singing becomes easier and smoother after vocal warm-up.36 Although these beliefs are held by many in the singing community5,37 and many speech-language pathologists,3,38 previous research has failed to demonstrate significant and consistent effects of classical vocal warm-up on the biomechanical or aerodynamic qualities of the voice.3,36–39 SPR offers an indirect objective observation of harmonic tuning of the vocal tract,34 which could be influenced by vocal warm-up.26 The purpose of this study was to examine how both classical warm-up and warm-up with semioccluded vocal tract tuning with a straw affected the formant structure of the singing voice. This study investigated whether the voice was acoustically different before versus after vocal warm-up and whether a classical warm-up affected the acoustics of the voice differently from phonating into a drinking straw while controlling for warm-up duration. Therefore, three specific questions were addressed in this study: (1) Does vocal warm-up condition (no warm-up, traditional warm-up, semioccluded warm-up) significantly alter the singing power ratio (SPR) of the singing voice? (2) Does SPR differ with vowel type (/i/, /o/, /ʌ/, /e/)? (3) Is effort, quantified by perceived phonatory effort, affected by warm-up condition (no warm-up, traditional warm-up, semioccluded warm-up)? Our hypothesis for the first question was that semioccluded vocal tract warm-up would lower the SPR more than no warm-up or traditional warm-up. For the second question, we

Emily Duke, et al

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Traditional vocal warm-up vs semioccluded vocal tract exercises

hypothesized that SPR would be lower for /i/ and /e/, based on previous findings.29 Finally, we expected PPE to be increased under the no warm-up condition and would be decreased by the traditional warm-up and semioccluded warm-up, with the greatest decrease happening under the semioccluded warm-up.

METHODS Thirteen men participated in the study, ranging in age from 19 to 42 years (M ¼ 22.615, standard deviation ¼ 5.785). Women were not included in this study as the singer’s formant is difficult to identify in the typical female range. Participants professed singing styles that included classical, jazz, pop, opera, Southern gospel, rock, folk, and show tunes. Singing experience ranged from a few years to 35 years. See Table 1 for participant demographic information. The participants participated in three different conditions: (1) no warm-up, (2) classical warm-up, and (3) semioccluded vocal tract warm-up with a straw. These conditions occurred at least 1 day apart at approximately the same time of day. Conditions were counterbalanced to minimize order effects. For each condition, a recording was made of the participant singing the Star Spangled Banner. The participant wore a headset microphone that was coupled with a Marantz PMD 671 recorder with a 44 kHz sampling rate and a 32-bit quantization rate (Marantz Europe, Eindhoven, The Netherlands). For the purpose of acoustic analysis, the participants were directed to sustain the /i/ of ‘‘free,’’ /o/ of ‘‘home,’’ /ʌ/ of ‘‘the,’’ and /e/ of ‘‘brave’’ of the last line for one second each. A stimulus pitch was provided with a pitch pipe. Participants identifying as tenors started on F4 in the key of BXmajor, and participants identifying as baritones or basses started on EX in the key of AX major. Perceived phonatory effort (PPE) was determined with a visual analog scale, 100 mm long (left anchor ¼ no voicing effort; right anchor ¼ maximum voicing effort). The participants were oriented to the scale before use and placed a mark on the line that represents the level of effort used. The distance in millimeters from the left end to the mark indicated the participants’ PPE.

Condition 1 was a baseline measure of the voice with no warm-up. The participant was asked to sing the Star Spangled Banner and to hold out the selected vowels of the last line for three trials with a 1 minute rest between each recording. Data from condition 2 was collected after a video-taped classical warm-up based on literature of Western singing.7,10 An experienced music professor with expertise in vocal pedagogy directed the video-recorded warm-ups. Each voice part (baritone or tenor) was instructed in a separate video. The warm-up tasks included (1) stretching, (2) resonance balancing, (3) register unification exercises, (4) messas di voce, and (5) agility/flexibility exercises. In total, the classical warm-up lasted approximately 9minutes with 6 minutes’ time of actual singing. Data from condition 3 was collected after semioccluded vocal tract straw warm-up. An instructional video40 guided participants on how to phonate into a plastic drinking straw of 5 mm diameter for a semioccluded vocal tract warm-up. This straw diameter, common in drinking straws, was chosen instead of a smaller diameter ‘‘coffee stirrer’’ straw because it allowed first time users a level of comfort achieving the semioccluded vocal tract position over a large range of pitches.16 The semioccluded vocal tract warm-up consisted of singing the entire Star Spangled Banner through the straw repeatedly for 6 minutes. For each condition, the participant completed a PPE rating form after singing the Star Spangled Banner. Acoustic analysis was performed on singing samples recorded at each data collection session using TF-32 time-frequency analysis software program (Milenkovic, University of Wisconsin, Madison, WI).41 From the sung vowels of the recordings, the amplitude and frequency of the first four resonance peaks and SPR were determined. A linear predictive code yielded the frequency and amplitude of each resonance peak. Calculating SPR required manually measuring the highest resonance peak between 2 and 4 kHz and the highest resonance peak between 0 and 2 kHz and dividing the low frequency peak amplitude by the high frequency peak amplitude. A low SPR would indicate greater amplitude in the high frequency formants, indicating possible presence of a singer’s

TABLE 1. Demographics of Participants Participant 01 02 03 04 05 06 07 08 09 10 11 12 13

Age 22 20 42 21 20 20 25 20 20 22 19 21 22

Voice Type Baritone Baritone Tenor Tenor Bass Baritone Tenor Tenor Tenor Tenor Bass Tenor Baritone

Singing Style

Years Singing

Classical Classical Classical Jazz, pop, opera, Southern gospel Classical, opera Opera, jazz, pop, rock, classical Gospel, classical Rock/pop, folk Gospel, jazz Pop, classical Classical, pop, Southern gospel (barbershop), choral Pop Pop, show tunes, classical (in the past)

10+ 8 35 10 5 10 ‘‘Maybe 10’’ ‘‘a few’’ 6 10 ‘‘My whole life’’ 6 ‘‘My whole life’’

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formant. A high SPR would indicate less amplitude in the higher frequency formants and absence of a singer’s formant.

RESULTS Data were analyzed using IBM SPSS statistics software (version 21; IBM, Armonk, NY).42 Raw data were examined visually for skewness and kurtosis. The Kolmogorov-Smirnov test of normality confirmed that all data were normally distributed. To answer the question of whether there is a significant difference in SPR outcome when analyzing the vowels /i, o, ʌ, e/ across three conditions, data were analyzed with repeated-measures analysis of variance (RM-ANOVA). The dependent variable was SPR. The two within-subjects factors were vowel (i, o, ʌ, e) and warm-up condition (baseline, traditional, and semioccluded). Table 2 lists the complete RMANOVA results. The main effects for vowel, condition, and the vowel condition interaction were tested using the multivariate criterion of Wilks’s lambda (L). SPR differed significantly across vowel, L ¼ 0.153, F(3, 10) ¼ 18.391, P ¼ 0.000, h2 ¼ 0.847. Pairwise comparisons for vowel revealed the following significant differences: the SPR values for the /i/ vowel were significantly lower than the SPR values for the /o/, /ʌ/, and /e/vowels; the SPR values for the vowel /e/ were found to be significantly lower than the /o/ and /ʌ/ vowels, and the SPR values for the vowel /ʌ/ were significantly lower than the /o/ vowel. Table 3 lists the results from the complete pairwise comparison analysis. The summary statistics in Table 4 indicate the lower SPR value for the /i/ vowel when compared with the other vowels. No significant difference was detected for warm-up condition, L ¼ 0.996, F(2, 11) ¼ 0.023, P ¼ 0.977, h2 ¼ .004. A statistically significant interaction was also not observed between vowel and warm-up condition, L ¼ 0.683, F(6, 7) ¼ 0.543, P ¼ 0.763, h2 ¼ .317. Table 4 lists the summary statistics for SPR outcome data across condition. To answer the question of whether there was a significant difference in PPE across three warm-up conditions, data were analyzed with a one-way within-subjects analysis of variance (RM-ANOVA). The dependent variable was PPE and the one within-subjects factor was warm-up condition (baseline, traditional, and semioccluded). Table 5 lists the complete RMANOVA results. PPE did not differ significantly across the

TABLE 3. P Values for Pairwise Comparisons Between Mean SPR Values of Each Vowel

Vowel /i/ Vowel /o/ Vowel /ə/ Vowel /e/

Vowel /i/

Vowel /o/

Vowel /ə/

0.000* 0.000* 0.005*

0.057 0.002*

0.002*

Vowel /e/

* Indicates significance.

warm-up conditions, L ¼ 0.753, F(2, 11) ¼ 1.808, P ¼ 0.209, h2 ¼ 0.247, indicating that warm-up condition did not significantly influence PPE. To establish reliability, 23% (ie, three participants) of the sample was selected for reanalysis. To establish interrater reliability another person involved with the study also analyzed the data. The first and second raters measurements of SPR were strongly correlated (rinter ¼ 0.964) and yielded a mean absolute difference of 0.005 SPR. DISCUSSION Three questions were asked in this study. The first question addressed in this study asked whether singing power ratio (SPR) would differ across warm-up condition. Our hypothesis was that SPR would be lowest for the semioccluded vocal tract condition because previous findings have indicated that semioccluded vocal tract exercises have resulted in greater amplitude of high frequency formants to low frequency formants.14 The present study found that SPR did not differ across warm-up condition. A second question investigated in this study was whether SPR would differ significantly across vowels. Our hypothesis was that SPR would be lower for vowel sounds /i/ and /e/. SPR did differ significantly across vowel, with SPR being lowest on /i/, followed by /e/, /ʌ/, and /o/. The third question asked was whether PPE was affected by

TABLE 4. Summary Statistics SPR

TABLE 2. Repeated Measures Within-Subjects Analysis of Variance Results for the Effect of Vowel and Warm-Up Condition on Singing Power Ratio SPR Source

df

F

P

Vowel Error Condition Error Vowel 3 Condition Error

3 10 2 11 6 7

18.391

0.000

0.023

0.977

0.543

0.763

Vowel i i i e e e o o o ə ə ə

Condition

M

SD

N

Baseline Traditional Semioccluded Baseline Traditional Semioccluded Baseline Traditional Semioccluded Baseline Traditional Semioccluded

1.093 1.026 1.060 1.202 1.222 1.239 1.470 1.498 1.458 1.354 1.385 1.351

0.215 0.209 0.186 0.138 0.138 0.173 0.318 0.218 0.305 0.200 0.265 0.233

13 13 13 13 13 13 13 13 13 13 13 13

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Traditional vocal warm-up vs semioccluded vocal tract exercises

TABLE 5. One Way Within-Subjects Analysis of Variance Results for the Effect of Warm-Up Condition on Perceived Phonatory Effort PPE Source

df

F

P

Condition Error

2 11

1.808

0.209

warm-up. PPE was expected to be highest under the no warmup condition. PPE did not differ significantly across any of the warm-up conditions. These results could be interpreted to mean that PPE while singing was not affected by warm-up condition. The present study found that SPR was not significantly altered by either warm-up condition. This finding has implications for the use of vocal warm-up in preparation for singing. Despite universal use of vocal warm-up exercise among singers, little is known about what vocal warm-up achieves physiologically or acoustically.2 A possible goal for singers in performing vocal warm-up is to establish vocal comfort and improve voice quality, the latter of which has perceptual descriptors with acoustic correlates. Ekholm et al35 found positive correlation between perceptual judgments of ‘‘resonance/ ring’’ and ‘‘color/warmth’’ with spectral area in the singer’s formant range and low ‘‘clarity/focus’’ ratings with high inharmonic noise levels. Certain exercises may be selected to improve the perceptual qualities such as ring, warmth, or vibrato of the voice.35 For example, sustained nasal consonants (humming) are useful to balance the resonances of the coupled oral and nasal cavities,7 which may contribute to a perceptual ‘‘ring.’’35 Another proposed purpose of vocal warm-up is to warm the vocal fold muscles in the same fashion as an athletic warm-up for the body.37 The most notable physiological changes from warm-up for physical activity are increased blood flow and increased skeletal muscle temperature.37 These changes are intended to result in improved skeletal muscle dynamics to avoid injury and to prepare an individual for athletic demands.43 The limited evidence available does not indicate that significant physiological change takes place after vocal warm-up.38,39 In fact, vocal warm-up has been found to increase PTP,39 the mechanisms by which are still largely unknown. It could be hypothesized that little voice function difference may be measured pre/post vocal warm-up because the muscles of the larynx have already been used for airway protection and speaking voice before the warm-up. Additionally, the larynx serves as a primary buffer between the ambient environment and the body’s internal core temperature (Sandage et al).45 This unique physiological role of the larynx compared with limb skeletal muscle may indicate physiological differences that we are not currently able to identify with our present acoustic measures. In the clinical setting, certain vocal warm-ups may still be appropriate for singing voice rehabilitation. Many vocal exercises used in this study have research-substantiated claims for

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improved vocal output, including straw phonation12,13,15 and nasal consonants.11 Thus, these exercises could be appropriate for improving vocal quality and reducing PPE. That said, questions regarding vocal warm-up remain, and no empirical studies have examined whether either traditional vocal warm-up exercises or straw phonation can improve voice production for an injured singer. Limitations to this study included that most of the participants were younger men. In addition, the warm-ups were short in duration, including 6 minutes of total singing time each (approximately 10 minutes including instruction). That said, some literature advises against warm-ups exceeding 20–30 minutes to avoid fatigue,5 and singing teachers have reported that their ideal vocal warm-up period lasts 5–10 minutes.2 From that standpoint, the relatively short warm-up could be considered a strength of the study. The question of duration is complicated, as bioenergetics of skeletal muscle would indicate that a warm-up activity requiring quick contractions instead of steady slow contractions may fatigue fast-twitch muscles.46 Fasttwitch type II fibers are a significant component of the laryngeal muscle make-up,47,48 so this is an important consideration. Muscle fatigue in vocal warm-up is considered something to be avoided,3,36 but in warm-up for limb skeletal muscle, fatigue is considered essential for endurance training.37 From this standpoint, the vocal warm-up tasks of the present study may have not been of sufficient length to develop fatigue. Third, a video-led warm-up was a contrived set-up. A true vocal warm-up would be more nuanced based on individual singer needs and would involve more teacher interaction in the context of a lesson. Finally, measuring SPR may be a limitation because of its lack of specificity. Although SPR allowed for standardized measurement of acoustics, it is not a validated measure and did not indicate whether the singer’s formant was present or absent, simply whether formant frequencies greater than 2 kHz had more intensity relative to formant frequencies below 2 kHz. PPE results could have been affected by the inner diameter of the straw used in the semioccluded vocal warm-up. Had a smaller diameter straw been used, two outcomes could have occurred. Considering small diameter straws (2 mm) require more than twice the subglottal pressure of a medium diameter straw (5 mm),44 the individual may perceive higher overall effort due to higher respiratory effort. It is also possible a smaller diameter straw would result in decreased glottal resistance, making phonation perceptually easier for the individual.17 This could have caused the participants to rate their PPE lower after straw phonation. Future studies may focus on the lasting effects of vocal warm-up on acoustic aspects of the voice by measuring beyond the moments immediately after warm-up. This may be completed by using a similar protocol to the present study but waiting some time before making a recording for acoustic measurement. Instead of measuring the singer’s formant via SPR, future studies may isolate the singer’s formant, verifying its presence or absence. In addition, future research should investigate the effect of straw diameter and length on PPE to standardize research investigations of semioccluded straw exercises.

6 CONCLUSIONS In conclusion, the present study did not find statistically significant changes in SPR across warm-up conditions. This was in opposition to the hypothesis that semioccluded warm-up would cause a decrease in SPR. SPR was statistically significant across vowels, with /i/ having the most significant SPR. This agrees with previous findings and supports the hypothesis regarding vowels and SPR. PPE did not differ significantly across warm-up condition, despite the expectation that traditional or semioccluded warm-up would cause a decrease in PPE. REFERENCES 1. Barr S. Singing warm-ups: physiology, psychology, or placebo? Logop Phoniatr Vocol. 2009;34:142–144. 2. Gish A, Kunduk M, Sims L, McWhorter AJ. Vocal warm-up practices and perceptions in vocalists: a pilot survey. J Voice. 2012;26:e1–e10. 3. Milbrath RL, Solomon NP. Do vocal warm-up exercises alleviate vocal fatigue? J Speech Lang Hear Res. 2003;46:422–436. 4. Hylton JB. Comprehensive Choral Music Education. Upper Saddle River, NJ: Prentice Hall; 1995. 5. Miller R. Warming up the voice. J Sing. 1990;46:22–23. 6. Shear P. Sing with power, range, and control. Can Musician. 2008;30:32. 7. Titze IR. The five best vocal warm-up exercises. J Sing. 2001;57:51–52. 8. Gregg JW. What humming can do for you. J Sing. 1996;52:37–38. 9. Nix J. Lip trills and raspberries: ‘‘High split factor’’ alternatives to the nasal continuant consonants. J Sing. 1996;55:15–19. 10. Miller R. The Structure of Singing. New York: Schirmer; 1986. 11. Verdolini K, Druker DG, Palmer PM, Samawi H. Laryngeal adduction in resonant voice. J Voice. 1998;12:315–327. 12. Andrade PA, Wood G, Ratcliffe P, Epstein R, Pijper A, Svec JG. Electroglottographic study of seven semi-occluded vocal tract exercises: LaVox, straw, lip-trill, tongue-trill, humming, hand-over-mouth, and tongue-trill combined with hand-over-mouth [published online ahead of print Feb 19 2014]. J Voice. 2014; http://dx.doi.org/10.1016/j.jvoice.2013.11.004. 13. Guzman M, Laukkanen A, Krupa P, Svec JG, Geneid A. Vocal tract and glottal function during and after vocal exercising with resonance tube and straw. J Voice. 2013;27:e19–34. 14. Laukkanen AM, Horacek J, Havlik R. Case-study magnetic resonance imaging and acoustic investigation of the effects of vocal warm-up on two voice professionals. Logoped Phoniatr Vocol. 2012;37:75–82. 15. Vampola T, Laukkanen AM, Horacek J, Svec JG. Vocal tract changes caused by phonation into a tube: a case study using computer tomography and finite element modeling. J Acoust Soc Am. 2011;109:310–315. 16. Titze IR. Voice training and therapy with a semi-occluded vocal tract: rationale and scientific underpinnings. J Speech Lang Hear Res. 2006;49:448–459. 17. Titze IR, Laukkanen AM, Finnegan EM, Jaiswal S. Raising lung pressure and pitch in vocal warm-ups: the use of flow-resistant straws. J Sing. 2002;58:329–338. 18. Laukkanen AM, Lindholm P, Vilkman E. On the effects of various vocal training methods on glottal resistance and efficiency. Folia Phoniatr Logop. 1995;47:324–330. 19. Gaskill CS, Erickson ML. The effect of a voiced lip trill on estimated glottal closed quotient. J Voice. 2008;22:634–643. 20. Titze IR. Lip and tongue trills—What do they do for us? J Sing. 1996;52: 51–53. 21. Story BH, Laukkanen AM, Titze IR. Acoustic impedance of an artificially lengthened and constricted vocal tract. J Voice. 2000;14:455–469. 22. Schwarz K, Cielo CA. Vocal and laryngeal modifications produced by the sonorous tongue vibration technique. Pro-Fono. 2009;21:161–166. 23. Titze IR, Laukkanen AM. Can vocal economy in phonation be increased with an artificially lengthened vocal tract? A computer modeling story. Logop Phoniatr Vocol. 2007;32:147–156.

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