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Proceedings of Meetings on Acoustics

Volume 19, 2013 http://acousticalsociety.org/

ICA 2013 Montreal

Montreal, Canada

2 - 7 June 2013

Musical Acoustics

Session 2aMU: Aeroacoustics of Wind Instruments and Human Voice I

2aMU8. Vibrato rate variability in three professional singing styles: Opera, Rock and

Brazilian countryGuilherme Pecoraro*, Daniella F. Curcio and Mara Behlau

*Corresponding au thor's address: Otolaryngology, HCFMUSP, Rua Marcelo Muller 1297, São Paulo, 03223060, SP, Brazil,

[email protected]

Vibrato is one of the most expressive aesthetic characteristics of singing voice. Indicative of good voice quality is typical of lyrical singing butit is also found in others styles of popular music. Acoustically, vibrato is defined as a long-term periodic modulation of the fundamentalfrequency. It occurs as a result of the laryngeal muscular system and is comprised of 3 main parameters: rate, extent and amplitude variation.The main controversy refers to the physiological mechanism of vibrato production, specifically concerning its neurological conscious control, aswell as the intra-subject variability of its acoustic parameters. In this study, we compare the characteristics related to vibrato rate (VR), assessing423 emissions, from recorded samples, produced by 15 professional singers, publicly and artistically acclaimed in occidental culture, torepresent 3 music styles: opera, rock and Brazilian country (sertanejo). We analyzed the samples through GRAM 5.01 and found that the VRwas kept constant intra-subject, independently of the singing style. The mean values for the VR for opera and Brazilian country singers werehigher than for rock singers. Effects of vocal training, kinship and aging on the vibrato rate, as well as technical skills to control it are objects of our future studies.

Published by the Acoustical Society of America through the American Institute of Physics

Pecoraro et al.

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INTRODUCTION

Vibrato has drawn the attention of voice researchers as it is an important stylistic element in singing voice. It'scharacterized by a number of acoustic and physiological features that may vary according to cultural tradition andmusical context.

Acoustically, the vibrato corresponds to a periodical sinusoid modulation of the fundamental frequency (Fo). Itmay be measured in terms of the number of modulation cycles per second, the vibrato rate and (Hertz) and thevibrato extent, the range of frequency variation of the cycles (Hertz); the vibrato onset is also an important

parameter, and it is defined as the delay (ms) from the phonation onset to the first vibrato cycle [1,2,3,4]. Variationsin loudness (dB) can also be considered and may also be used and a stylistic feature [5].

Vibrato has been considered as a remarkable sign of good vocal quality [6] as it important to bring out the voicefrom the musical background [7], and is used as an aesthetic resource. Certain characteristics allow for untrainedlistener to perceptually identify professional from untrained singers [8], young from senile singers, pathologicalfrom healthy voices. Stability and steadiness of vibrato periodicity has been considered as indicators of good vocalquality, and the mean vibrato rate values usually range from 4 a 7 Hz. [9,10].

The variability of the acoustic parameters involved in the vibrato are still a controversial issue in the literatureand have been considered as to be related to tone pitch [11] and loudness [12], the duration of sustained emissions[13], music style [14,15], vocal technique [16] and senility [17].

AIM

To investigate the variability of the vibrato rate in singers of three music styles: opera, rock and Brazilian country.

METHOD

Five singers from each music style, considering their artistic relevance and representativity (TABLE 1). In theBrazilian country style we analyzed the first voice of the duo, which is the one with the highest pitch, performing themain melodic line.

TABLE 1. Selected singers per musical style.MUSICAL

STYLESINGERS

Classical LucianoPavarotti Plácido Domingo Mario Del Monaco Giuseppe Di Stefano Alfredo Krauss

Rock AndréMatos Bruce Dickinson Ian Gillan Ronnie James Dio Jeff Scott Soto

Sertanejo Gian eGiovani Leandro e Leonardo Chitãozinho e Xororó Chrystian e Ralf Zezé di Camargo e

Luciano

We acoustically analyzed 423 sustained emissions in vibrato with at least 20 vibrato cycles each. Using thecomputer program GRAM5.0.1, we digitized the samples under standardized settings to analyze the correspondentnarrow band spectra. Each sample should have from three to five vibrato cycles [29]. We did not control variablesrelated to tone frequency and intensity, since the literature supports that such parameters do not interfere with thevibrato rate. [18,19]. Through direct reading from the computer program we calculated the vibrato rate by dividingthe number of vibrato cycles by the time lapse between them. We based the acoustic analyses on the sharpest andsteadiest harmonic of each sample. Figure 1 displays spectrograms of samples obtained for each singe in the threestudied groups.

We considered intra-subject, intra and inter-group variations to investigate the variability of the vibrato rate andsearch for possible correlations. To analyze intra-subject variability we obtained the coefficient of variation(standard deviation divided by the average, multiplied by 100) and considered homogeneous any setting of valueswhich produced a coefficient of variation equal or under 30. To compare intra and intergroup data, we used theKruskal-Wallis test, with a significance level of 5%.

Pecoraro et al.

Proceedings of Meetings on Acoustics, Vol. 19, 035026 (2013) edistribution subject to ASA license or copyright; see http://acousticalsociety.org/content/terms. Download to IP: 143.107.176.125 On: Thu, 05 Jun 2014 12:55:14

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RESULTS AND DISCUSSION

Because we used a method of visual analysis of narrow band spectra to select the samples, it was possible to usecommercially available CDs [20]. This procedure also allows for the clear identification of the singer's voice fromconcomitant instruments' sounds and/or backing vocals.

TABLE 2. Vibrato rate mean, standard deviation, mode, minimum and maximum values and coefficient of variation persinger: opera group.

DI STEFANO PAVAROTTI DEL MONACO KRAUS DOMINGOMEAN 5.53 6.14 6.15 5.32 5.71

SD 0.21 0.22 0.29 0.31 0.31

MODE 5.32 6.25 6.17 5.16 5.68

MIN 5.17 5.68 5.75 4.95 5.1

MAX 5.88 6.58 6.76 6.33 6.56

VARIATION 3.80 3.75 4.72 5.83 5.43*p<=5% (Kruskal-Wallis)

TABLE 3. Vibrato rate mean, standard deviation, mode, minimum and maximum values and coefficient of variation persinger: rock group.

MATOS DICKINSON GILLAN DIO SOTOMEAN 5.48 4.75 5.58 4.66 5.11

SD 0.60 0.43 0.35 0.47 0.34

MODE 5.66 4.76 5.77 4.17 5.00

MIN 3.92 3.88 4.95 3.91 4.59

MAX 6.38 5.75 6.38 5.95 5.88

VARIATION 10.95 9.05 6.27 10.09 6.65*p<=5% (Kruskal-Wallis)

TABLE 4. Vibrato rate mean, standard deviation, mode, minimum and maximum values and coefficient of variation persinger: Brazilian country group (Sertanejo).

GIAN LEONARDO XORORÓ CHRYSTIAN ZEZÉMEAN 5.83 6.26 5.71 5.58 6,30

SD 0.30 0.27 0.41 0.43 0,41

MODE 5.56 5.95 6.12 5.21 6,25

MIN 5.32 5.81 4.65 4.76 5,62

MAX 6.52 6.67 7.14 6.38 7,35

VARIATION 5.15 4.15 7.18 7.71 6,51

*p<=5% (Kruskal-Wallis)

According to the literature, the vibrato rate usually ranges from 4 to 7 Hz, similarly to frequency ranges of someinvoluntary oscillatory activity of other muscles in the human body in different situations, such as physiologicaltremor (5-15 Hz), essential tremor (6-10 Hz), and Parkinson's disease tremor (4-8 Hz) [21]. Since our findingssupport that there are no intra-subject differences in what concerns vibrato rate variability (TABLES 2, 3 and 4), wereinforce the rational of a physiological neurological mechanism that would limit the variability of the vibrato rate[1,3,7,22,23,24,25].

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TABLE 5. Vibrato rate mean, standard deviation, mode, minimum and maximum values and distribution distortion perstudied group: opera, rock and Brazilian country (Sertanejo).

ÓPERA ROCK SERTANEJOMEAN 5.77* 5.04 5.91*

SD 0.42* 0.57 0.47*

MODE 5.75* 5.00 6.25*

MIN 4.95* 3.88 4.65*

MAX 6.76* 6.38 7.35*

VARIATION 7.29* 11.31 7.95*

*p<=5% (Kruskal-Wallis)

In what concerns intra-group comparisons, the mean value of the vibrato rate of opera singers was equivalent tothat obtained for the Brazilian country singers, and both were higher in comparison to rock singers (Kruskal-Wallis

p<=.05). We hypothesize that this may be related to the different kinds of laryngeal adjustments performed by operaand Brazilian country singers, in comparison to rock singers, in terms of vocal folds strain and/or presence ofsupraglottic phonatory activity, as well as general muscular tension and how this factor interact in the resulting vocal

quality [26-28]Based on our clinical experience with professional singers and our trained perceptual skills to evaluate vocal

quality, we believe that rock singers may intentionally control the vibrato rate and use it in a particular way as aninterpretative feature, in comparison to opera and Brazilian country singers (TABLE 5), even though the intra-subject variation for these singers was not enough to be accused by statistical analysis. On this matter, especially forrock singers, studies with a larger sample size could bring significant information, by exploring the variability ofother vibrato parameters, besides the vibrato rate, such as vibrato extent and loudness oscillation.

CONCLUSION

The vibrato rate obtained for opera and Brazilian country singers was equivalent, and both were higher in

comparison to rock singers. There was no significant difference in the vibrato rate in what concerns intra subject orintra group variability.

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