Acoustic and aerodynamic measures in singers: a comparison between genders

ABSTRACT

Purpose

Compare acoustic and aerodynamic voice measures between male and female singers.

Methods

A cross-sectional, observational, comparative study conducted with a convenience sample. Study participants were 30 male and 30 female singers. Acoustic (vocal intensity and fundamental frequency) and aerodynamic (expiration time, air pressure, expiratory and voice airflow, expiratory volume, aerodynamic power and resistance, acoustic impedance, and aerodynamic efficiency) measures were assessed during emission of the syllable /pá/, at usual frequency and intensity, for seven consecutive times. These emissions enable extraction of air pressure measures (obtained by the plosive consonant /p/, which estimates glottic pressure), as well as of airflow and acoustic voice measures (obtained by the vowel /a/ and the syllable /pá/).

Results

Women presented higher values of fundamental frequency compared with those of men. No differences were identified in the evaluation of aerodynamic measures between the groups.

Conclusion

Values of aerodynamic measures do not differ between male and female singers.

Keywords
Voice; Acoustics; Evaluation; Music; Dysphonia

RESUMO

Objetivo

Comparar medidas acústicas e aerodinâmicas da voz em homens e mulheres cantores.

Método

Trata-se de um estudo transversal, observacional, comparativo, com amostra de conveniência. Participaram do estudo 30 homens e 30 mulheres cantores. Foi realizada avaliação das medidas acústicas (intensidade e frequência fundamental) e aerodinâmicas (tempo de expiração, pressão aérea, fluxo de ar expirado e vozeado, volume expiratório, potência e resistência aerodinâmica, impedância acústica e eficiência aerodinâmica) durante a emissão da sílaba /pá/ em frequência e intensidade habituais, sete vezes consecutivas. Estas emissões permitem a extração de medidas de pressão aérea (obtidas da consoante plosiva /p/ que estima a pressão glótica) e das medidas de fluxo aéreo e acústicas da voz (obtidas da vogal /a/ da sílaba /pá/).

Resultados

Na comparação de homens e mulheres cantores, as mulheres apresentam maiores valores de frequência fundamental, e não houve diferenças na avaliação de valores das medidas aerodinâmicas entre os gêneros.

Conclusão

Os valores das medidas aerodinâmicas não se diferenciam entre mulheres e homens cantores.

Descritores
Voz; Acústica; Avaliação; Música; Disfonia

INTRODUCTION

An individual’s vocal quality results from the interaction of aerodynamic forces characterized by expired airflow, myoelastic forces of the larynx, in addition to contributions of the vocal tract filter⁽¹⁾. The larynx functions as a transducer, converting aerodynamic energy into acoustic energy. The airflow is transformed into acoustic energy by means of the opening and closing cycles of the vocal folds. The respiratory system is responsible for providing the energy needed for phonation; therefore, impairments in this system may affect professionals who use their voice as a working tool⁽²⁾.

Voice production presents a multidimensional function, and through assessment of the different vocal parameters is possible to (1) quantify voice quality more accurately; (2) understand the effects of a given treatment, either surgical, pharmacological, or phonotherapeutic; and (3) correlate the different vocal evaluation data for a better understanding of the functional mechanisms involved in phonation^(2-3).

Assessment of the aerodynamic measures of singers is of utmost importance, because they use respiration as a basis for the adequate production of the quality of their singing voice. Increased airflow and subglottic pressure can occur at any moment, and any respiratory or laryngeal inefficiency may impair vocal production⁽⁴⁾. The specific scientific literature reports that singers differ from the general population regarding the values of aerodynamic measures because of the muscular training they perform⁽⁵⁾. Singers tend to present lower airflow and subglottic pressure values than non-singers, demonstrating that these professionals have greater aerodynamic efficiency⁽⁶⁾.

A study conducted with singers of different musical styles observed that the aerodynamic measures of subglottic pressure and expiratory volume were different, because each singer makes particular vocal adaptations to language, type of music, interpretation, and individual characteristics ⁽⁴⁾.

Singing requires control and precision of breathing and phonation and, consequently, greater glottal airflow efficiency⁽⁶⁾. Lack of harmony in one of the functions of these systems can generate imbalances and affect the ability to maintain adequate sound quality⁽⁷⁾. An individual with good respiratory training in singing uses glottal airflow properly.

Aerodynamic analysis of the voice is becoming increasingly viable and common in clinical practice in vocal health as a result of scientific advances. The first aerodynamic measurements were direct, thus invasive, considering that they measured subglottic pressure through puncture of the cricothyroid membrane⁽⁸⁾. Technological advances enabled extraction of aerodynamic measures indirectly, and parameters of airflow and subglottic pressure began to be estimated by intraoral pressure measurements⁽⁹⁾.

Anatomical and functional differences in the larynx and the acoustic characteristics of the voice of men and women have been previously analyzed in the literature comprehensively ^(10-12). However, few studies have investigated differences in the aerodynamic parameters of airflow and subglottic air pressure associated with gender^(13-15), and no studies analyzing these differences in singers have been found.

Understanding the acoustic and aerodynamic characteristics of the voice in singers and the differences between these aspects regarding gender is of fundamental importance to subsidize the vocal training of singers. It is known that the anatomical differences between the male and female vocal apparatus interfere with the acoustic characteristics of the voice^(10-12) and with the aerodynamic parameters of the spoken voice^(13-15), but the differences generated by gender in the acoustic and aerodynamic parameters of the voice of singers have not yet been studied in the specific literature. It is assumed that male and female singers present different acoustic and aerodynamic measures of the voice as a result of anatomical differences in the larynx and respiratory system.

In this context, the objective of this study was to compare acoustic and aerodynamic voice measures between male and female singers.

METHODS

This cross-sectional, observational, comparative study was conducted with a convenience sample and approved by the Research Ethics Committee of the Universidade Federal de Minas Gerais (UFMG) under protocol no. CAAE 48085815.2.0000.5149. All participants were informed about the objectives and procedures of the study and signed an Informed Consent Form (ICF).

Study participants were 60 individuals of both genders: 30 men aged 19-48 years (mean=28.6) and 30 women aged 18-36 years (mean=26.1). The groups were matched for age (p =0.208), musical genre, and singing experience time. All participants were selected at singing schools.

Inclusion criteria were as follows: professional or amateur singers with absence of vocal complaints and/or impairments and presence of normal larynx, aged 18-55 years - because this is considered the period of greater vocal stability, thus eliminating any impairment associated with the phase of voice change or with aging. Exclusion criteria comprised smokers, pregnant women, or women in the menstrual period.

Laryngeal assessment was performed through high-speed videolaryngoscopy, which accurately and clearly captures the glottic opening and closing phases, using a Computerized Speech Lab (CSL) Kay Pentax™ Model 6103 console (Lincoln Park, NJ, USA), by a single otolaryngologist. Larynxes whose exams presented complete glottic closure were considered normal, or in the cases of women with posterior triangular cleft, and without lesions in both vocal folds.

All participants were evaluated for presence of vocal and voice quality complaints by a speech-language pathologist with expertise in voice and over five years of practice. Participants without vocal complaint and with neutral vocal quality were included in the study.

With respect to characteristics of the singing voice, the participants were divided into popular and classical singers according to the musical genre reported. In the group of women, 21 (70%) were popular singers with 4-12 years (mean=7.3) of experience and nine (30%) were classical singers with 3-10 years (mean=6.6) of experience. In the group of men, 19 (63.3%) were popular singers and 11 (36.7%) were classical singers, with 5-13 years (mean=7.5) and 4-15 years (mean=6.9) of experience, respectively.

Acoustic and aerodynamic measures of voice were obtained with the CSL Kay Pentax™ Model 6103 program (Lincoln Park, NJ, USA) with a Phonatory Aerodynamic System (PAS) module installed in a Dell®, Optiplex GX260 personal computer and a Direct Sound® professional sound card at the Observatory of Functional Health in Speech-Language Pathology of the Medical School of UFMG (OSF/UFMG). These measures were obtained through emission of the syllable /pá/ at usual frequency and intensity for seven consecutive times. According to the manual “Phonatory aerodynamic system: a clinical manual Kay Pentax™” , these emissions enable extraction of air pressure measures (obtained by the plosive consonant /p/, which estimates glottic pressure), as well as of airflow and acoustic voice measures (obtained by the vowel /a/ and the syllable /pá/)⁽¹⁶⁾.

Aerodynamic measures were recorded using a silicone face mask placed on the participant's mouth. This mask was coupled to a device connected to a pressure transducer, and the intraoral pressure was measured by means of a small-diameter polyethylene catheter inserted into the mask through a lateral orifice and positioned in the central part of the participant's tongue; the other end of the catheter was attached to the pressure transducer ( Figure 1 ).

Figure 1
Illustration of the Kay Pentax® Model 6103 console (Lincoln Park, NJ, USA) in use

Acoustic measures of vocal intensity and fundamental frequency (f ₀) were obtained using a unidirectional condenser microphone attached to the back of the face mask. All signals from the transducer and the microphone were sent to the CSL program for analysis. The acoustic and aerodynamic measurements were conducted in acoustically treated environment, with ambient noise <50 dBNPS defined by an Instrutherm® Model DEC-490 sound pressure level meter.

The following acoustic parameters were analyzed:

• Maximum intensity: maximum value of vocal intensity measured in dBNPS.

• Mean intensity: mean value of vocal intensity measured in dBNPS.

• Mean intensity of voiced segments: mean intensity value considering the voiced segments measured in dBNPS.

• Fundamental frequency (f₀): mean value of the fundamental frequency measured in Hz.

The aerodynamic measures assessed were grouped into five categories as follows:

1. 1

   Temporal Measure:

• Expiration time: it measures the expired airflow time, or positive airflow, in seconds.

1. 2

   Air pressure measures:

• Peak air pressure: this measure is the highest value of air pressure observed in the emission of one or more plosive syllables, measured in cm H₂O.

• Mean peak air pressure: it is mean value of peak air pressure, measured in cm H₂O.

1. 3

   Airflow measures:

• Peak expiratory airflow: it is maximum value of the expiratory air flow, measured in L/s.

• Peak voiced airflow: this measure represents the mean airflow of voiced speech segments, measured in L/s.

• Mean airflow during voicing: it is the quotient of the total expiratory air volume by the duration of voiced segments, measured in L/s.

1. 4

   Volume measure

• Expiratory volume: this measure is the total volume of expiratory air measured in liters.

1. 5

   Aerodynamic measures

• Aerodynamic power: is the product of the mean peak air pressure value, the air flow during voicing, and the conversion factor 0.09806, measured in watts.

• Aerodynamic resistance: is the quotient of the mean peak air pressure value by the air flow during voicing, measured in cm H2O/(L/s). It is equivalent to the acoustic impedance measure multiplied by the conversion factor 0.9806.

• Acoustic impedance: is the quotient of the mean peak air pressure value by the air flow during voicing measured in dyne s/cm⁵.

• Aerodynamic efficiency: this is a dimensionless value defined in parts per million (ppm) that represents the quotient of acoustic power by aerodynamic power.

Statistical analysis of the data was processed using the Statistical Package for the Social Sciences (SPSS 17.0). First, a descriptive analysis of the data was performed with measures of central tendency and dispersion; after that, the non-parametric Mann-Whitney test was applied to the independent samples for cross analysis of the variables. A 95% confidence interval was considered for all statistical analyses.

RESULTS

Women presented higher values of fundamental frequency (f₀ ) compared with those of men. No differences were identified in the evaluation of aerodynamic measures between genders ( Table 1 ).

Table 1
Comparison of measures of habitual vocal emissions between male and female singers

Measures		Minimum	Maximum	Mean	SD	p-value
ACOUSTIC
Maximum intensity (dB)	Men	77.23	92.04	85.36	4.22	0.529
	Women	78.91	95.11	86.28	4.52
Mean intensity (dB)	Men	75.37	89.30	83.11	3.97	0.620
	Women	77.22	92.83	83.99	4.27
Mean intensity of voiced segments (dB)	Men	75.37	89.30	83.11	3.97	0.620
	Women	77.22	92.83	84.00	4.28
Fundamental frequency (Hz)	Men	96.94	221.07	166.75	31.87	0.023 *
	Women	126.43	245.71	186.49	32.37
TEMPORAL
Expiration time (s)	Men	0.62	1.31	0.95	0.17	0.192
	Women	0.48	1.30	1.00	0.18
AIR PRESSURE
Peak air pressure (cm H2O)	Men	4.41	13.94	9.58	3.06	0.813
	Women	4.82	13.94	9.47	2.88
Mean peak air pressure (cm H2O)	Men	3.81	13.49	8.94	2.83	0.501
	Women	4.41	13.49	8.59	2.76
AIRFLOW
Peak expiratory airflow (l/s)	Men	0.14	0.59	0.31	0.12	0.646
	Women	0.11	0.48	0.31	0.10
Peak voiced airflow (l/s)	Men	0.08	0.44	0.19	0.08	0.414
	Women	0.08	0.34	0.21	0.08
Air flow during voicing (l/s)	Men	0.08	0.42	0.18	0.08	0.354
	Women	0.08	0.33	0.19	0.08
VOLUME
Expiratory volume (l)	Men	0.05	0.47	0.18	0.09	0.295
	Women	0.06	0.40	0.21	0.10
AERODYNAMIC
Aerodynamic power (watts)	Men	0.04	0.44	0.17	0.09	0.941
	Women	0.04	0.44	0.18	0.11
Aerodynamic resistance (cm H2O/(l/s)	Men	12.76	67.75	45.26	13.52	0.304
	Women	19.95	67.47	41.63	12.14
Acoustic impedance (ds/cm5)	Men	13.02	69.12	45.87	14.30	0.387
	Women	20.35	68.80	42.53	12.43
Aerodynamic efficiency (ppm)	Men	101.09	324.12	202.16	76.26	0.662
	Women	90.39	376.30	211.94	76.78

• Mann-Whitney test
• ^*
  Statistical significance: p<0.05
• Captions: SD = standard deviation

DISCUSSION

The singing voice requires a refined coordination between the respiratory and phonatory systems. The ability to accurately and efficiently control airflow and subglottic pressure is important for singers to properly produce their musical repertoire⁽⁷⁾.

The minimum air pressure necessary to cause vocal fold vibration is described as Phonation Threshold Pressure (PTP)⁽¹⁷⁾, and the specific scientific literature reports that air pressure variation in a usual conversation varies from 0.3 to 1.2 KPa, but that these values are higher in singing ⁽¹⁸⁾, evidencing that the singing voice presents aerodynamic requirements greater than those of the spoken voice⁽²⁾. Studies comparing the characteristics of vocal cord nodule size with aerodynamic parameters in singers and non-singers found that the latter presented positive correlation between lesion size and airflow parameters. Such correlation was not observed in singers ⁽⁵⁾, suggesting that singing voice training favors the development of particular aerodynamic mechanisms that are present even in situations of glottal impairment.

Technological advances are making aerodynamic assessment of the voice increasingly common in vocal clinical practice⁽¹⁹⁾. Aerodynamic analyses can be used to detail phonological physiology and determine compensatory functional mechanisms in individuals with dysphonia⁽²⁰⁾. The literature describes that aerodynamic measures present good test-retest agreement⁽²⁰⁾ and are sensitive to evaluate dysphonic conditions, and should be used as a complementary voice assessment instrument⁽³⁾.

Results of this study show that women presented values of fundamental frequency (f ₀) higher than those of men. These results are consistent with the literature ^(15,21) and can be justified by the fact that the vocal folds of women and men differ with respect to the size and number of cycles of vibration per second⁽²²⁾. The natural vocal fold length and larynx size of females are smaller compared with those of males, thus the habitual values of f₀ are lower in men⁽²³⁾.

Some mean values of f₀ described in the literature for young Brazilian women are 206Hz⁽²¹⁾, 215.42Hz⁽²⁴⁾, and 208.28Hz⁽¹⁵⁾, whereas f₀ values of 120Hz⁽²¹⁾, 127.61Hz⁽²⁴⁾, and 136.56Hz⁽¹⁵⁾ are found for young Brazilian men. The f₀ values observed in this study for young women and men were 186.49Hz and 166.75Hz, respectively. These results are different from those described in the literature, which shows increased values for males and decreased values for females. The differences observed can be justified by the fact that this study evaluated the f₀ of singers, who can present different vocal adjustments according to their practice of the singing voice. Further studies are needed to understand whether vocal adjustments of the singing voice are really important to justify modifications in f₀.

Aerodynamic measurements are essential for studies on the physiological bases of voice production ⁽²⁵⁾. Aerodynamic assessment with extraction of airflow, air pressure and expiratory volume measures is recommended as part of a multidimensional assessment of the voice by the American Speech-Language-Hearing Association (ASHA)⁽²⁶⁾.

The present study shows that female and male singers do not present differences in aerodynamic measures regarding the parameters of expiration time, air pressure, airflow, expiratory volume, aerodynamic power and efficiency, and acoustic impedance. Studies conducted with speakers of Brazilian Portuguese have reported that aerodynamic measures of men and women are differentiated by the parameters of laryngeal resistance (quotient of the subglottic pressure values by the airflow values) and laryngeal efficiency (quotient of the vocal intensity values by the values of air pressure and airflow), with such values higher in the female gender⁽¹⁵⁾. These findings, despite being obtained with samples of the Brazilian population, can not be directly compared with those of the present study, because they were extracted using a different aerodynamic measurement equipment whose parameters and units of measurement are different from those used for the development of this study.

The literature shows that aerodynamic measures in English speakers differ according to gender regarding airflow values, with higher values observed either in men⁽²⁷⁾ or in women⁽¹³⁾, whereas air pressure measures were sensitive to gender in situations of dysphonic voices⁽¹⁴⁾. Although these studies used the same equipment to obtain the aerodynamic measures, the versions of the analysis software were different^(13,27), and dysphonic voices were also analyzed⁽¹⁴⁾. As for the participants' mother tongue, the surveys evaluated speakers of American ^(14,27) and Australian⁽¹³⁾ English. All of these variables can explain the differences observed in the literature. Studies addressing aerodynamic measures associated with gender in singers have not been found in the literature.

Understanding the aerodynamic and acoustic characteristics of the voice of male and female singers is important to define vocal and respiratory parameters in singing voice production.

Findings of this study demonstrate that male and female singers presented the same aerodynamic characteristics of the voice, evidencing that, unlike in spoken voice, gender interferes with measures of airflow^(13,27) and air pressure⁽¹⁴⁾, in singing voice the aerodynamic parameters of male and female singers are the same. These results suggest that singing voice training develops specific singing respiratory mechanisms that do not seem to be influenced by the anatomical differences of the vocal apparatus between men and women. Further studies conducted with male and female singers considering different musical genres are important in order to better understand the phonatory and respiratory mechanisms involved in singing, and how the different singing styles can influence the acoustic and aerodynamic parameters of the singing voice.

CONCLUSION

Female singers present higher fundamental frequency values than male singers. Values of aerodynamic measures do not differ between male and female singers speakers of Brazilian Portuguese.

• Study conduct at Programa de Pós-graduação em Ciências Fonoaudiológicas, Universidade Federal de Minas Gerais – UFMG - Belo Horizonte (MG), Brasil.
• Financial support: nothing to declare.

REFERÊNCIAS

• ¹
  Jiang JJ, Maytag AL. Aerodynamic measures of glottal function: what extra can they tell us and how do they guide management? Curr Opin Otolaryngol Head Neck Surg. 2014;22(6):450-4. http://dx.doi.org/10.1097/MOO.0000000000000107. PMid:25254405.
  » http://dx.doi.org/10.1097/MOO.0000000000000107
• ²
  Carroll LM, Sataloff RT, Heuer RJ, Spiegel JR, Radionoff SL, Cohn JR. Respiratory and glottal efficiency measures in normal classically trained singers. J Voice. 1996;10(2):139-45. http://dx.doi.org/10.1016/S0892-1997(96)80040-3. PMid:8734388.
  » http://dx.doi.org/10.1016/S0892-1997(96)80040-3
• ³
  Yiu EML, Yuen YM, Whitehill T, Winkworth A. Reliability and applicability of aerodynamic measures in dysphonia assessment. Clin Linguist Phon. 2004;18(6-8):463-78. http://dx.doi.org/10.1080/02699200410001703592. PMid:15573484.
  » http://dx.doi.org/10.1080/02699200410001703592
• ⁴
  Stone RE Jr, Cleveland TF, Sundberg J, Prokop J. Aerodynamic and acoustical measures of speech, operatic, and broadway vocal styles in a professional female singer. J Voice. 2003;17(3):283-97. http://dx.doi.org/10.1067/S0892-1997(03)00074-2. PMid:14513952.
  » http://dx.doi.org/10.1067/S0892-1997(03)00074-2
• ⁵
  Stepp CE, Heaton JT, Stadelman-Cohen TK, Braden MN, Jetté ME, Hillman RE. Characteristics of phonatory function in singers and non-singers with vocal fold nodules. J Voice. 2011;25(6):714-24. http://dx.doi.org/10.1016/j.jvoice.2010.06.003. PMid:21216129.
  » http://dx.doi.org/10.1016/j.jvoice.2010.06.003
• ⁶
  Connolly J, Gerwin H, Russell BA. The effects of vocal training on singers aerodynamic measures [Internet]. New York: State University of New York at Fredonia, Department of Speech Pathology & Audiology; 2013 [citado em 2017 Nov 11]. Disponível em: http://www.fredonia.edu/studentexpo/connr.htm
  » http://www.fredonia.edu/studentexpo/connr.htm
• ⁷
  Lundy DS, Roy S, Casiano RR, Evans J, Sullivan PA, Xue JW. Relationship between aerodynamic measures of glottal efficiency and stroboscopic findings in asymptomatic singing students. J Voice. 2000;14(2):178-83. http://dx.doi.org/10.1016/S0892-1997(00)80025-9. PMid:10875569.
  » http://dx.doi.org/10.1016/S0892-1997(00)80025-9
• ⁸
  Plant RL, Hillel AD. Direct measurement of subglottic pressure and laryngeal resistance in normal subjects and in spasmodic dysphonia. J Voice. 1998;12(3):300-14. http://dx.doi.org/10.1016/S0892-1997(98)80020-9. PMid:9763180.
  » http://dx.doi.org/10.1016/S0892-1997(98)80020-9
• ⁹
  Smitheran JR, Hixon TJ. A clinical method for estimating laryngeal airway resistance during vowel productions. J Speech Hear Disord. 1981;46(2):138-46. http://dx.doi.org/10.1044/jshd.4602.138. PMid:7253590.
  » http://dx.doi.org/10.1044/jshd.4602.138
• ¹⁰
  Lovato A, Colle W, Giacomelli L, Piacente A, Righetto L, Marioni G, et al. Multi-Dimensional Voice Program (MDVP) vs Praat for assessing euphonic subjects: a preliminary study on the gender-discriminating power of acoustic analysis software. J Voice. 2016;30(6):765.e1-5. http://dx.doi.org/10.1016/j.jvoice.2015.10.012. PMid:26975896.
  » http://dx.doi.org/10.1016/j.jvoice.2015.10.012
• ¹¹
  Yamauchi A, Yokonishi H, Imagawa H, Sakakibara KI, Nito T, Tayama N, et al. Quantitative analysis of digital videokymography: a preliminary study on age- and gender-related difference of vocal fold vibration in normal speakers. J Voice. 2015;29(1):109-19. http://dx.doi.org/10.1016/j.jvoice.2014.05.006. PMid:25228432.
  » http://dx.doi.org/10.1016/j.jvoice.2014.05.006
• ¹²
  Yamauchi A, Yokonishi H, Imagawa H, Sakakibara KI, Nito T, Tayama N, et al. Age and gender-related difference of vocal fold vibration and glottal configuration in normal speakers: analysis with glottal area waveform. J Voice. 2014;28(5):525-31. http://dx.doi.org/10.1016/j.jvoice.2014.01.016. PMid:24836359.
  » http://dx.doi.org/10.1016/j.jvoice.2014.01.016
• ¹³
  Goozée JV, Murdoch BE, Theodoros DJ, Thompson EC. The effects of age and gender on laryngeal aerodynamics. Int J Lang Commun Disord. 1998;33(2):221-38. http://dx.doi.org/10.1080/136828298247884. PMid:9709440.
  » http://dx.doi.org/10.1080/136828298247884
• ¹⁴
  Zhuang P, Sprecher AJ, Hoffman MR, Zhang Y, Fourakis M, Jiang JJ, et al. Phonation threshold flow measurements in normal and pathological phonation. Laryngoscope. 2009;119(4):811-5. http://dx.doi.org/10.1002/lary.20165. PMid:19263409.
  » http://dx.doi.org/10.1002/lary.20165
• ¹⁵
  Oliveira KV, Faria BS, Silva JPG, Reis C, Ghio A, Gama ACC. Análise das medidas aerodinâmicas no português brasileiro por meio do método multiparamétrico de avaliação vocal objetiva assistida (EVA). Rev CEFAC. 2013;15(1):119-27. http://dx.doi.org/10.1590/S1516-18462012005000053.
  » http://dx.doi.org/10.1590/S1516-18462012005000053
• ¹⁶
  Stemple J, Weinrich B, Brehm SB. Phonatory aerodynamic system: a clinical manual. Chicago: Kay Pentax; 2008.
• ¹⁷
  McHenry M, Evans J, Powitzky E. Singers phonation threshold pressure and ratings of self-perceived effort on vocal tasks. J Voice. 2013;27(3):295-8. http://dx.doi.org/10.1016/j.jvoice.2012.12.013. PMid:23462685.
  » http://dx.doi.org/10.1016/j.jvoice.2012.12.013
• ¹⁸
  Titze IR. Principles of voice production. 2nd ed. Lowa City: National Center for Voice and Speech; 2000.
• ¹⁹
  Schaeffer N. Pre- and poststimulation study on the phonatory aerodynamic system on participants with dysphonia. J Voice. 2017;2(2):254.e1-9. http://dx.doi.org/10.1016/j.jvoice.2016.06.020.
  » http://dx.doi.org/10.1016/j.jvoice.2016.06.020
• ²⁰
  Awan SN, Novaleski CK, Yingling JR. Test-retest reliability for aerodynamic measures of voice. J Voice. 2013;27(6):674-84. http://dx.doi.org/10.1016/j.jvoice.2013.07.002. PMid:24119644.
  » http://dx.doi.org/10.1016/j.jvoice.2013.07.002
• ²¹
  Felippe ACN, Grillo MHMM, Grechi TH. Normatização de medidas acústicas para vozes normais. Rev Bras Otorrinolaringol. 2006;72(5):659-64. http://dx.doi.org/10.1590/S0034-72992006000500013.
  » http://dx.doi.org/10.1590/S0034-72992006000500013
• ²²
  Hollien H. Vocal fold dynamics for frequency change. J Voice. 2014;28(4):395-405. http://dx.doi.org/10.1016/j.jvoice.2013.12.005. PMid:24726331.
  » http://dx.doi.org/10.1016/j.jvoice.2013.12.005
• ²³
  Izadi F, Mohseni R, Daneshi A, Sandughdar N. Determination of fundamental frequency and voice intensity in iranian men and women aged between 18 and 45 years. J Voice. 2012;26(3):336-40. http://dx.doi.org/10.1016/j.jvoice.2011.05.008. PMid:21889298.
  » http://dx.doi.org/10.1016/j.jvoice.2011.05.008
• ²⁴
  Araujo SA, Grellet M, Pereira JC, Rosa MO. Normatização de medidas acústicas da voz normal. Rev Bras Otorrinolaringol. 2002;68(4):540-4. http://dx.doi.org/10.1590/S0034-72992002000400014.
  » http://dx.doi.org/10.1590/S0034-72992002000400014
• ²⁵
  Joshi A, Watts CR. Phonation Quotient in Women: A measure of vocal efficiency using three aerodynamic instruments. J Voice. 2017;31(2):161-7. http://dx.doi.org/10.1016/j.jvoice.2016.06.007. PMid:27430861.
  » http://dx.doi.org/10.1016/j.jvoice.2016.06.007
• ²⁶
  ASHA: American Speech and Hearing Association. Committee on Instrumental Voice Assessment Protocols – IVAP. Recommended protocols for instrumental assessment of voice: draft summary of recommendations. Rockville: ASHA; 2015.
• ²⁷
  Zraick RI, Smith-Olinde L, Shotts LL. Adult normative data for the Kay Pentax Phonatory Aerodynamic System Model 6600. J Voice. 2012;26(2):164-76. http://dx.doi.org/10.1016/j.jvoice.2011.01.006. PMid:21600731.
  » http://dx.doi.org/10.1016/j.jvoice.2011.01.006

Publication Dates

• Publication in this collection
  08 Oct 2018
• Date of issue
  2018

History

• Received
  11 Nov 2017
• Accepted
  24 Jan 2018