Laryngoscopic, acoustic, perceptual, and functional assessment of voice in rock singers

In Key Words Rock singing · Growl voice · Falsetto · Singing voice · Singing Voice Handicap Index · Laryngoscopy · Acoustic analysis · Hyperfunction Abstract Objective: The present

Original Paper

Folia Phoniatr Logop 2013;65:248–256 DOI: 10.1159/000357707

Laryngoscopic, Acoustic, Perceptual,

and Functional Assessment of Voice in

Rock Singers

Marco Guzman a Macarena Barros c Fernanda Espinoza c Alejandro Herrera c

Daniela Parra c Daniel Muñoz b Adam Lloyd d

a School of Communication Sciences and b Faculty of Medicine, University of Chile, and c School of Communication

Sciences, Andres Bello National University, Santiago , Chile; d Voice Care Center, Ear, Nose, Throat, and Plastic Surgery

Associates, Orlando, Fla , USA

falsetto represent laryngeal and pharyngeal hyperfunctional activity, they did not seem to contribute to the presence of any major vocal fold disorder in our subjects Nevertheless,

we cannot rule out the possibility that more evident vocal fold disorders could be found in singers who use these tech-niques more often and during a longer period of time

© 2014 S Karger AG, Basel

Introduction

Voice quality in singing is affected by both laryngeal and vocal tract configuration The sound produced by the larynx is in turn determined by the vibratory patterns of the vocal folds These patterns vary depending on vocal registers (vocal fry, modal, falsetto, whistle), mode of phonation (pressed, normal, flow, breathy and whisper)

as well as singing style (belting, opera, rock, etc.) [1] Modifications of vocal tract configuration are impor-tant not only to produce phonetic-articulatory features, but also because it is an important way to shape the vocal quality Particularly, the lower vocal tract structures (epi-laryngeal tube, pyriform sinuses and hypopharynx) seem

to play a crucial role in the quality of the singing voice Earlier studies have reported that the lower part of the vo-cal tract changes depending on the style of singing In

Key Words

Rock singing · Growl voice · Falsetto · Singing voice ·

Singing Voice Handicap Index · Laryngoscopy ·

Acoustic analysis · Hyperfunction

Abstract

Objective: The present study aimed to vocally assess a group

of rock singers who use growl voice and reinforced falsetto

Method: A group of 21 rock singers and a control group of

18 pop singers were included Singing and speaking voice

was assessed through acoustic, perceptual, functional and

laryngoscopic analysis Results: No significant differences

were observed between groups in most of the analyses

Acoustic and perceptual analysis of the experimental group

demonstrated normality of speaking voice Endoscopic

eval-uation showed that most rock singers presented during

singing voice a high vertical laryngeal position, pharyngeal

compression and laryngeal supraglottic compression

Su-praglottic activity during speaking voice tasks was also

ob-served However, overall vocal fold integrity was

demon-strated in most of the participants Slightly abnormal

obser-vations were demonstrated in few of them Singing voice

handicap index revealed that the most affected variable was

the physical sphere, followed by the social and emotional

spheres Conclusions: Although growl voice and reinforced

Published online: March 18, 2014

Marco Guzman © 2014 S Karger AG, Basel

sical singing, wide pyriform sinuses and a wide

hypophar-ynx, as well as a narrow epilaryngeal tube have been

ob-served [2, 3] According to Sundberg [4, 5] , the area ratio

between these two last structures would be the main

expla-nation for the singer’s formant cluster On the other hand,

during belting (singing technique used in pop styles,

musi-cal theater and others) a narrow hypopharynx, pyriform

sinuses and epilaryngeal tube have been observed [4, 5]

Moreover, in different singing styles it is common to

find vocal sounds that would probably be categorized as

pathological vocal qualities if they were produced by

non-singers during conversational voice usage However,

these sounds are typically used as expressive and stylistic

vocal resources by some contemporary commercial

mu-sic singers One of these vocal resources is the so-called

growl voice, which is commonly used in jazz, blues, pop,

gospel and rock among others [6, 7] Moreover, similar

productions have been found in ethnic singing from

Brazil, Japan and South Africa [8] When this vocal

re-source is used in rock, it is also called death growl, death

metal vocals, guttural vocals, death grunts, unclean

vo-cals, and harsh vocals [9]

Perceptually, the growl voice is similar to other types

of vocal qualities such as roughness and hoarseness,

which are considered perceptual signs of voice disorders

Nevertheless, the growl voice is always a vocal effect or

expressive emphasis and is typically not a permanent way

to produce voice [10] Even though some singers use

growl voice extensively during a song, it is usually not

found in normal speaking voice phonation [11]

According to Sakakibara et al [12] growl voice is

pro-duced through the simultaneous vibration of the vocal

folds and laryngeal supraglottic structures The vocal

folds vibrate periodically and the aryepiglottic folds

gen-erate subharmonics These subharmonics have also been

found in other studies [13–15] A radiologic study showed

that during growl voice production the larynx rose to the

fourth vertebra and there was a large anterior-posterior

(A-P) laryngeal constriction [12] In addition, some

sub-jects demonstrated vibration of both right and left

aryepi-glottic folds in phase, whereas in other singers the phase

was slightly different and in some instances aryepiglottic

vibration was completely aperiodic and unstable

An important group of performers that commonly use

growl voice are rock singers, specifically in some rock

subgenres such as screamo, thrash metal, nu metal, black

metal, heavy metal, death metal, and hardcore punk [16]

Rock singers not only use growl voice as part of their

vocal technique, but also many other vocal resources such

as the reinforced falsetto The naive falsetto (falsetto

with-out training) is characterized by a decreased degree of glottal adduction, a reduction in amplitude of the electro-glottographic signal which may come from a reduction of the contact surface area between the vocal folds, which could be related to a reduction in the thickness of the vo-cal folds compared to modal register [17–19] The rein-forced falsetto usually presents a greater glottal adduction, and hence sounds louder, brighter and has more

harmon-ic energy in the high spectral region (2–5 kHz) than naive falsetto [20] Musical styles where singers may use rein-forced falsetto are: blues, glam rock, epic metal, soul, etc The reinforced falsetto in contemporary commercial mu-sic is usually associated with a shortening of the vocal tract and a very open mouth configuration Perceptually, it may sound pressed and similar to screaming [20]

Since both growl voice and reinforced falsetto are probably produced with laryngeal and vocal tract con-strictions, they could be labeled as vocal resources based

on hyperfunctional vocal activity, which in turn might be potentially harmful to the phonatory mechanism Never-theless, there are no empirical studies supporting this as-sumption The present study aimed to perceptually, acoustically, functionally, and laryngoscopically assess a group of rock singers who use growl voice and/or rein-forced falsetto In particular, the question was explored of whether or not frequent use of growl voice and reinforced falsetto in singing had an effect on the characteristics of the speaking voice

Methods

Participants Twenty-one rock singers (19 men and 2 women) participated

as subjects in the present study (experimental group) Their aver-age aver-age was 26 years, with a range from 19 to 34 years All were native Spanish speakers and recruited from amateur rock bands Since one of the authors of the present study (A.H.) belongs to the singing rock field, he contacted and recruited the participants The inclusion criteria were: (1) experience producing growl voice and/

or reinforced falsetto for at least 1 year, and (2) practice of the tech-nique at least 4 times a month during performances or rehearsals None of the participants reported previous voice therapy/training None of the participants had a hearing impairment All partici-pants were asked to explain and produce the voice techniques they use in rock singing before undergoing endoscopic examination This procedure was perceptually verified by 4 of the authors of the present study, all of whom were speech-language pathologists with experience in singing voice

A control group was also included in the present study Eigh-teen pop singers (14 men and 4 women) with more than 2 years of experience performing different pop styles (except rock) were re-cruited for the same voice assessment Their average age was 28 years, with a range from 20 to 32 years The experiments were

con-ducted with the understanding and the written consent of each

participant Participants from both experimental and control

groups underwent an evaluation session lasting no more than 1 h

This session included (1) application of the Singing Voice

Handi-cap Index (S-VHI), (2) voice recording, and (3) laryngoscopic

eval-uation Individual explanation and demonstrations were provided

about the required tasks before performing the examinations.

Questionnaire Application

All participants were asked to complete the Spanish adaptation

and validation of the S-VHI This self-administrated questionnaire

is a health status instrument designed to assess the voice handicap

resulting from singing voice problems [21, 22] The S-VHI has

im-portant psychometric properties of reliability and validity It

con-tains 36 items chosen to address the physical, emotional, social,

and economic impact of singing voice problems Each item is

in-dividually scored on a 5-point Likert scale anchored by ‘never’

(score of 0) and ‘always’ (score of 4).

Recording Procedure

Subjects were required to produce three repetitions of a

sus-tained vowel /a/ using a comfortable fundamental frequency and

loudness level; each vowel was sustained for 6 s The vowel

produc-tions were recorded in an acoustically treated booth, with an

ambi-ent noise level below 30 dB For the recording, a Focusrite Saffire

6 USB interphase (Focusrite, Calif., USA) and an omnidirectional

condenser microphone (Samson MM01, Samson Technologies

Corp., Hauppauge, N.Y., USA) positioned at a distance of 20 cm

from the mouth, with a 45° inclination angle was used Samples

were digitally recorded using Steinberg Cubase LE4 (Steinberg,

Germany) software in a WAV format at a sampling rate of 44.1

kHz with 16 bits/sample quantization

Acoustic Analysis

Acoustic analysis of all recorded sustained vowels included

har-monic-to-noise ratio (HNR), frequency perturbation measure

(jit-ter), and amplitude perturbation measure (shimmer) They were

ob-tained by PRAAT software, version 5.0.23 (Bergsma & Weenink,

2008) Recorded samples were edited prior to acoustic analysis The

first and last second of each sample were excluded, leaving the

cen-tral 4 s for analysis The editing procedure was carried out using

Goldwave v5.58 software (GoldWave Inc., St John’s, Nfld., Canada).

Laryngoscopic Assessment

After voice recordings, participants underwent a

laryngoscop-ic examination They were asked to sit upright in a comfortable

chair Assessment of laryngeal activity was carried out with a

flex-ible fiberoptic endoscope (Pentax VNL-1170K, KayPENTAX,

Lin-coln Park, N.J., USA) connected to a video camera and a light

source Analog images were digitalized with a Pentax EPK-1000

(KayPENTAX) digital processor All examinations were

per-formed without topical nasal anesthesia The laryngoscopic

proce-dure was carried out by a laryngologist with more than 20 years of

experience in singing and speaking voice assessment During

sing-ing voice tasks, the flexible endoscope was placed near the tip of

the uvula, allowing a full view of the pharynx and larynx This

placement was set by securing the fiberscope against the alar

car-tilage of the nose with the laryngologist’s finger A steady

place-ment of the fiberscope is crucial since observation of laryngeal

height adjustments and other laryngeal configurations can be

af-fected by movement of the endoscope During regular speaking endoscopic procedures, the flexible endoscope was placed right above the epilaryngeal tube For the purposes of this study, two main aspects were observed during the laryngoscopic procedure: (1) regular speaking voice laryngoscopic assessment (for both groups), and (2) assessment during production of growl voice and reinforced falsetto (only for the experimental group) Phonatory tasks during the first stage were: sustained vowels and running speech tasks To assess growl voice, subjects from the experimental group were asked to produce a sustained vowel /a/ using a com-fortable fundamental frequency (middle range) and loudness level

To evaluate reinforced falsetto, participants were required to pro-duce a sustained vowel in the highest possible pitch using the most comfortable vowel and loudness level Recall that not all the par-ticipants produced both growl voice and reinforced falsetto This information was previously obtained during the recruitment pro-cess Possible laryngeal constrictions, vertical laryngeal position and pharyngeal activity were assessed during both growl voice and reinforced falsetto after laryngoscopic recording was made Visual Evaluation of Laryngoscopic Samples

Two fellowship-trained laryngologists blinded to the purpose and nature of the study were asked to review the laryngoscopic ex-aminations and rate the degree of A-P laryngeal compression, me-dial laryngeal compression, pharyngeal constriction, and vertical laryngeal position on a 5-point scale For vertical laryngeal posi-tion 1 = very low, 5 = very high, for medial laryngeal compression

1 = very opened, 5 = very narrow, for A-P laryngeal compression

1 = very opened, 5 = very narrow, and for pharyngeal width 1 = very wide, 5 = very narrow Moreover, raters were asked to evalu-ate the presence of masses, edema, erythema, glottal chink, and other possible laryngeal alterations (presence  = 1, absence  = 0) This visual assessment was performed for videos obtained from both experimental and control groups For the experimental group only, a similar visual evaluation was carried out to evaluate growl voice and reinforced falsetto The degree of medial and A-P laryn-geal compression, medial larynlaryn-geal compression, pharynlaryn-geal con-striction, and vertical laryngeal position was assessed on the same 5-point scale All sound was removed Each laryngoscopic exami-nation could be reviewed as many times as desired

Perceptual Evaluation Voice audio samples of sustained vowels from both experimen-tal and control groups were perceptually assessed by 3 external rat-ers All three repetitions of the vowel (from each participant) were used for this part of the analysis This group of blinded judges con-sisted of speech-language pathologists with at least 8 years of expe-rience working with patients with voice disorders The order of recordings was randomized Perceptual assessment was performed with the GRBAS scale [23] The GRBAS scale evaluates five param-eters: G = grade of dysphonia, R = roughness, B = breathiness, A = asthenic quality, and S = strain quality Perceptual variables were assessed using a 4-point scale (from 0 to 3), where 0 = normal, 1 = slight, 2 = moderate, and 3 = severe Raters could replay each sam-ple as many times as they wanted before making their determina-tion and moving on to the next recording The evaluadetermina-tion was per-formed in a sound-treated room using a laptop computer and a high-quality Audioengine loudspeaker (Audioengine, Kowloon, Hong Kong) The listeners were located at approximately 2 m from the loudspeaker All the listeners reported normal hearing.

Statistical Analysis

Descriptive statistics were calculated for the variables,

includ-ing mean and standard deviation A kappa test was performed to

assess the interrater concordance for each auditory perceptual

pa-rameter and cut-off point of >0.60 was used Intraclass correlation

coefficients were computed to assess intrarater concordance

Moreover, a Spearman correlation analysis between acoustic

pa-rameters, S-VHI and perceptual assessment was performed; the

correlational analysis only used the G (grade) dimension from the

GRBAS scale.

The results and the comparisons between experimental and

control groups were assessed using Wilcoxon’s rank-sum test for

continuous variables, and χ 2 test and Fisher’s exact for categorical

variables A p value <0.05 was considered to be statistically

sig-nificant Stata 12.0 (StataCorp 2011, College Station, Tex., USA:

StataCorp LP) statistical software was used for analysis.

Results

Acoustic Analysis

Results (mean and standard deviation) of acoustic

analysis for experimental and control groups are

present-ed in table 1 Group means showpresent-ed normal values for

jit-ter, shimmer, and HNR The normal threshold for jitter

and shimmer was considered to be 1 and 3%, respectively

HNR greater than 10 dB was considered normal There

were no significant differences between both groups

Laryngoscopic Evaluation

Table 2 shows the results from the intra- and interrater

reliability analysis A good intrarater concordance was

demonstrated for each judge Moreover, the 2 blinded

judges obtained high agreement (interrater reliability) for

all laryngoscopic features (kappa value >0.60) No

signif-icant differences were found between groups for all

laryn-goscopic features Therefore, there are no structural or

functional laryngeal differences when comparing rock

and pop singers

Of the 21 subjects from the experimental group, 7

(33.3%) presented with normal laryngeal anatomy This

includes normality of all laryngeal structures including

the vocal folds The remaining participants demonstrated

varying degrees of alteration in some laryngeal structures

Eight of them presented with slight vocal fold erythema,

and 9 singers showed a slight degree of edema in the

pos-terior laryngeal commissure (possibly due to

laryngeal-pharyngeal reflux) Moreover, 2 subjects presented with

slight asymmetry of the false vocal folds and 5

partici-pants demonstrated excessive laryngeal mucous No mass

lesions (polyps, nodules, cysts, edemas, etc.) were found

in any participant

During phonation, of the total number of rock singers (n = 21), 15 (71.4%) showed normal laryngeal function, including that of the vocal folds The remaining partici-pants presented some degree of abnormality Four of them demonstrated a slight glottal chink Furthermore, slight arytenoid asymmetry was observed in 3 subjects during phonation Despite these slight alterations, none of them demonstrated a major functional laryngeal problem When considering supraglottic tissue function during conversational voice usage, 16 participants (66.6%) from the experimental group demonstrated supraglottic com-pression Nine of them showed A-P compression, 4 pre-sented medial compression, and 3 prepre-sented both A-P and medial compression

Growl Voice and Reinforced Falsetto Laryngoscopic Assessment

Table 3 presents the results from intra- and interrater reliability analysis for growl voice and reinforced falsetto

A good intrarater concordance was demonstrated for each judge Moreover, the 2 blinded judges obtained high

Table 1. Mean and standard deviation of acoustic analysis for ex-perimental and control groups

Experimental Control p value

Shimmer 1.55±0.54 1.68±0.51 0.4924

Table 2. Intra- and interrater reliability analysis for laryngoscopic assessment

interrater (kappa;

p value)

intrarater (ICC;

p value)

i nterrater (kappa;

p value)

intrarater (ICC;

p value)

Pharyngeal

ICC = Intraclass correlation coefficient; VLP = vertical laryngeal posi-tion; MLC = medial laryngeal compression; LC = laryngeal compression.

agreement (interrater reliability) for all laryngoscopic

variables in both growl voice and reinforced falsetto

Figure 1 and table  4 show the scores from both growl

voice and reinforced falsetto Significant differences were

found between groups for vertical laryngeal position and

A-P laryngeal compression No differences were

demon-strated for medial laryngeal compression and pharyngeal

constriction

Twelve of the 21 participants produced reinforced

falsetto and 15 produced growl voice Therefore, 6

sing-ers performed both techniques All singsing-ers who

formed reinforced falsetto chose the vowel /a/ to

per-form the required high pitch and presented a high

verti-cal laryngeal position and open-mouth configuration

during examination Moreover, in 5 of the 12

partici-pants (41.6%) a medial laryngeal compression was

ob-served Four subjects (33.3%) presented both medial and

A-P compression The remainder (n = 3, 25%) did not

demonstrate laryngeal compression during reinforced

falsetto phonation Additionally, pharyngeal

constric-tion was demonstrated during endoscopic examinaconstric-tion

in 11 of the 12 participants (92%) during reinforced

fal-setto phonation

For growl phonation, A-P supraglottic compression was

observed in only 15 participants One participant showed

only medial compression (7%) In most of the participants

who produced growl voice (n = 11, 73%), both medial and A-P supraglottic compression was demonstrated Further-more, pharyngeal constriction was demonstrated in 10 participants (67%) Thirteen singers (87%) produced a ver-tical laryngeal position change Four of them demonstrated

a higher vertical laryngeal position compared to the rest level Most of them (9 subjects) presented a lower vertical laryngeal position during growl voice

Table 3. Intra- and interrater reliability analysis for growl voice and reinforced falsetto

(interrater)

ICC (p value) (intrarater)

(interrater)

ICC (p value) (intrarater)

ICC = Intraclass correlation coefficient.

0 1 2 3 4 5

Vertical laryngeal position Medial laryngealcompression A-P laryngealcompression constrictionPharyngeal

Growl Falsetto Growl Falsetto Growl Falsetto Growl Falsetto

Fig 1. Scores from growl voice and reinforced falsetto techniques

Table 4. Scores from growl voice and reinforced falsetto

techniques

Growl voice

Reinforced falsetto

p value

Vertical laryngeal position 2.96±1.44 4.70±0.33 0.0004

Medial laryngeal compression 4.06±0.90 4.04±0.72 0.4693

A-P laryngeal compression 4.53±0.69 3.58±0.82 0.0032

Pharyngeal constriction 4.06±0.97 4.54±0.39 0.0639

Table 5. Mean and standard deviation of S-VHI for experimental and control groups

Experimental Control p value Physical 19.28±9.01 12.33±6.45 0.0154

Emotional 1.57±2.03 1.73±2.37 0.8277

Questionnaire Results

Results (mean and standard deviation) of S-VHI for

experimental and control groups are presented in table 5

Significant differences were found in physical and social

spheres between groups There were no differences for

emotional and economic spheres Total scores were also

significantly different between groups

For the experimental group, results showed that the

highest rated variables were in the physical sphere, rated

19.28 ± 9.01 points (26.78%) from the total of 72 possible

points However, even the highest rating was less than a

third of the total possible points The ratings were

typi-cally 1 = almost never (18 subjects, 85.7%) or 2 =

some-times (3 subjects, 14.3%)

Subjects from the experimental group responded

‘al-most never’ in the physical sphere (52.38%) for the

vari-able ‘It takes a lot of effort to sing’ The rest (47.61%)

re-sponded ‘almost never’ for the variables ‘I have trouble

making my voice do what I want it to’ and ‘I have trouble

controlling the raspiness in my voice’ Therefore, more

than half of the subjects reported that almost never they

have the sensation of effort during singing

The social sphere was the second most affected

vari-able in the experimental group (1.57 ± 2.03 points,

19.64%), followed by the emotional sphere (8.19 ± 7.33

points, 14.47%), from the total of 56 points and 8 points,

respectively Moreover, it is important to mention that

the most common response in all items of the emotional

sphere was the option 0 = never (9 subjects, 43%) The less

affected S-VHI variable was the economic sphere (0.42 ±

0.87 points, 5.35%)

Perceptual Evaluation

Results of the perceptual evaluation by raters using

the GRBAS scale for experimental and control groups

indicated that all the parameters obtained a kappa value

above 0.60 and p value <0.05, except roughness for the

control group Therefore, there was a high interrater

concordance for most of perceptual variables Asthenia (A) demonstrated the lowest value (0) and grade of dys-phonia (G) the highest value (0.34) for the experimental group Moreover, the 2 blinded judges obtained high intrarater reliability There were no significant differ-ences between both groups for any of the perceptual parameters

Correlation Analysis The results of correlation analysis are presented in ta-ble 6 Statistically significant correlation (p value <0.05) was found between grade of dysphonia (G) and HNR Moreover, jitter correlated with shimmer and HNR No correlations were found with S-VHI

Discussion

The term ‘edgy voice’ is defined as all the sounds that are commonly used by rock singers and sound like a dis-tortion of the ‘clean voice’ Some of these edgy sounds are growling, guttural voice, raspy voice and pressed high notes [24] The present study aimed to perceptually, acoustically, functionally, and laryngoscopically assess a group of 21 rock singers who use two of these ‘edgy’ sounds: growl voice and reinforced falsetto

Results revealed that both the growl voice and the rein-forced falsetto are characterized by supraglottic compres-sion, pharyngeal constriction and changes in vertical la-ryngeal position The rough and raspy perceptual quality

of growl voice production is likely produced by the vibra-tion of the supraglottic structures involved in the observed laryngeal compression Borch et al [25] assessed the acoustic and physiology of ‘distorted tones’ in rock singers and found significant supraglottic activity including the aryepiglottic folds, anterior part of the mucosa covering the arytenoids, and ventricular folds (medial compres-sion) An earlier investigation performed in growl voice

Table 6. Spearman correlation analysis between acoustic parameters, S-VHI and perceptual assessment for the experimental group

HNR rho = –0.31; p = 0.1576 rho = –0.70; p = 0.003 rho = –0.68; p = 0.007 1 –

G rho = 0.30; p = 0.1855 rho = 0.26; p = 0.2422 rho = 0.38; p = 0.086 rho = –0.46; p = 0.0328 1 From perceptual analysis through GRBAS scale, only G (grade of dysphonia) was used.

technique also showed simultaneous vibration of

laryn-geal supraglottic structures [12] In the present study,

growl voice demonstrated a significantly higher degree of

aryepiglottic (A-P) compression than reinforced falsetto

More than 70% of subjects from the experimental

group demonstrated not only aryepiglottic constriction,

but also medial supraglottic compression during growl

voice Fuks et al [13] in a high-speed video study

report-ed approximation and self-sustainreport-ed ventricular fold

vi-bration in different singing modes, one of which was

sim-ilar to Mongolian bass-type singing (perceptually simsim-ilar

to growl voice quality) Additionally, Lindestad et al [26]

analyzed the bass-type throat singing The ventricular

folds had low amplitude of vibration with incomplete

closure

The supraglottic laryngeal activity found in the present

study during singing could be considered a

hyperfunc-tional behavior and hence a possible risk factor for

devel-oping a voice disorder for the singers who frequently use

it Several definitions of laryngeal hyperfunction exist,

but a recurrent feature in almost all descriptions includes

excessive laryngeal musculoskeletal activity, force, or

ten-sion [27, 28] The basic paradigm that evaluates laryngeal

hyperfunction is to look for compression of the

supra-glottic structures during phonation [29] This

supraglot-tic activity may be separated into two components: (1)

A-P supraglottic activity and (2) medial supraglottic

ac-tivity [30–32] In the present study most of the

partici-pants from the experimental group not only

demonstrat-ed laryngeal supraglottic activity during singing, but 14 of

them (67%) also presented with some slight degree of

la-ryngeal supraglottic activity during speaking voice tasks

Therefore, it would be possible to speculate that these

subjects (rock singers) could have laryngeal

hyperfunc-tion, maybe caused by the use of growl voice and

rein-forced falsetto during singing Nevertheless, when

com-paring supraglottic laryngeal activity between groups

during speaking voice tasks, no significant differences

were found Therefore, it is unlikely that the slight

hyper-function observed during speaking is caused by growl

voice and reinforced falsetto

Despite the apparent widespread acceptance of these

postures as endoscopic signs of vocal hyperfunction,

some studies have shown that this supraglottic activity

could be present in subjects with normal voice [20, 30, 33,

34] Sama et al [33] assessed the prevalence of laryngeal

hyperfunction in two groups: subjects diagnosed with

functional dysphonia and a group of subjects with normal

voice No differences were found Similarly, Stager et al

[30] found the presence of anterior-posterior

compres-sion in patients with nodules, functional dysphonia, and normal voice

The fact that both acoustic and perceptual analysis in the present study revealed normal and quasi-normal voices, respectively, might be another reason to question that the supraglottic activity present in rock singers dur-ing speakdur-ing voice tasks is really a sign of laryngeal hyper-function and hence a risk factor for vocal fold injury In addition, significant correlation was found between per-ceptual grade of dysphonia (G) and all the acoustic pa-rameters Moreover, no significant differences were found between groups when comparing acoustics and perceptual data

The laryngeal and pharyngeal configurations observed during both growl voice and reinforced falsetto in most

of participants is not surprising since previous studies have reported these compressions as normal and even desirable vocal adjustment in various styles of singing Studies carried out with belters suggested that this tech-nique is typified by epiglottis tilted over the larynx [35] Yanagisawa et al [3] also reported aryepiglottic constric-tion during twang, belting, and opera qualities Pershall

et al [36] demonstrated similar results Supraglottic compression has also been found in Middle Eastern sing-ing [37] In addition, there is empirical evidence that A-P constriction can contribute to an acoustic advantage (voice quality) [5, 38]

Even though growl voice possesses a quality that may sound pressed or constricted, the major work may not be performed by the vocal folds, but by the laryngeal supra-glottic structures and pharynx This assumption is based

on the fact that some vocal coaches teach their students

to produce a breathy voice quality before adding the vi-bration of supraglottic structures when producing growl voice Moreover, it is also taught that growl voice should not be produced by tightening the vocal folds, but to relax them and using more abdominal support (abdominal muscle contraction instead of laryngeal effort) [24, 39, 40] This might explain the laryngoscopic normality found in most of our participants

The reinforced falsetto demonstrated high vertical la-ryngeal position, phala-ryngeal constriction and supraglot-tic compression However, they may not be possible causes of the slight vocal folds alterations found during laryngoscopy The use of adequate resonance strategies to avoid an excessive vocal fold muscle effort during high pitch phonation might be a suitable explanation The res-onance strategies used during reinforced falsetto in high pitches were assessed in the same subject group in a pre-vious study [20] Authors reported that high values of the

two first vocal tract formant frequencies (F1 and F2) were

observed in all participants A clear increase of the

spec-tral energy in one or two harmonics due to the

coinci-dence or proximity with one or two formants was

dem-onstrated in all singers These outcomes would imply that

the total sound pressure level of the radiated sound

dur-ing reinforced falsetto production may not be supported

by increasing vocal effort (high glottal resistance and high

subglottic pressure), but by an adequate vocal tract

con-figuration strategy Borch et al [25] reported the same

formant changes in rock singing They stated that the

val-ues reflected a relatively high larynx position and open

mouth configuration In this regard, earlier studies have

demonstrated that a similar vocal tract configuration is

classically displayed by sopranos during production of

high pitches to avoid laryngeal muscle effort [41–43]

Additionally, according to Titze and Story [44] , Story

et al [45] and Titze [46] , an important clinical issue

per-tains to the conflict of accepting (and even encouraging)

the use of a narrow epilaryngeal tube for healthy voice

production The authors state that the source-filter

inter-action and vocal tract inertance may be increased by

nar-rowing the epilaryngeal tube in an A-P direction

There-fore, this A-P narrowing could constitute a benefit for

vocal fold oscillation and vocal fold abduction [44–46]

Although, there is some evidence that the supraglottic

activity demonstrated in the present study might not be a

real hyperfunctional and detrimental laryngeal behavior,

it is not possible to assure that over a longer period of time

the same results would be found Most of our participants

only practice growl voice and reinforced falsetto

occa-sionally (at least 4 times a month) and also most of them

have been using these techniques for about 1 year

Furthermore, the possibility that rock singing might

be harmful to the phonatory mechanism cannot be ruled

out A previous investigation revealed that rock style is

characterized by higher values of subglottic pressure,

closed quotient, and pitch range than other nonclassical singing styles Moreover, regarding mode of phonation, rock singing was perceptually rated as the most pressed style among the others This was objectively corroborated

by the lowest normalized amplitude quotient value (high degree of phonatory pressedness) [47, 48] Loud phona-tion and high subglottic pressures were also found in rock singing in a study conducted by Borch et al [25]

Functional assessment through S-VHI showed results that seem to be in line with the above-mentioned find-ings Although the most affected variable was the physical sphere and it was higher in rock singers than in pop sing-ers, it was affected only in 26.78% of the experimental group Furthermore, most subjects responded 1 = almost never or 2 = sometimes These outcomes could indicate that participants do not consider they have a significant physical impairment with their singing voice

Conclusions

Although both growl voice and reinforced falsetto have physiologic characteristics that are usually associ-ated with laryngeal hyperfunction (high vertical

larynge-al position, pharyngelarynge-al constriction and both medilarynge-al and A-P supraglottic compression), they do not seem to con-tribute to laryngeal disorders in the assessed group of rock singers Perceptual, acoustic, functional and laryn-goscopic assessment demonstrated no major alterations

in most of the participants Likely a proper resonance strategy in reinforced falsetto and a decreased glottal ad-duction in growl voice could be the factors that contribute

to the avoidance of voice problems in singers that use these vocal resources that are classically labeled vocal abuse We do not overlook the possibility that vocal fold disorders could be found if singers used these techniques more frequently and for longer periods of time

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