Acoustic Parameters Critical for an Appropriate Vibrato

High and Wide: An In Silico Investigation of Frequency, Intensity, and Vibrato Effects on Widely Applied Acoustic Voice Perturbation and Noise Measures

OBJECTIVES

This in silico study explored the effects of a wide range of fundamental frequency (fo), source-spectrum tilt (SST), and vibrato extent (VE) on commonly used frequency and amplitude perturbation and noise measures.

METHOD

Using 53 synthesized tones produced in Madde, the effects of stepwise increases in fo, intensity (modeled by decreasing SST), and VE on the PRAAT parameters jitter % (local), relative average perturbation (RAP) %, shimmer % (local), amplitude perturbation quotient 3 (APQ3) %, and harmonics-to-noise ratio (HNR) dB were investigated. A secondary experiment was conducted to determine whether any fo effects on jitter, RAP, shimmer, APQ3, and HNR were stable. A total of 10 sinewaves were synthesized in Sopran from 100 to 1000 Hz using formant frequencies for /a/, /i/, and /u/-like vowels, respectively. All effects were statistically assessed with Kendall's tau-b and partial correlation.

RESULTS

Increasing fo resulted in an overall increase in jitter, RAP, shimmer, and APQ3 values, respectively (P < 0.01). Oscillations of the data across the explored fo range were observed in all measurement outputs. In the Sopran tests, the oscillatory pattern seen in the Madde fo condition remained and showed differences between vowel conditions. Increasing intensity (decreasing SST) led to reduced pitch and amplitude perturbation and HNR (P < 0.05). Increasing VE led to lower HNR and an almost linear increase of all other measures (P < 0.05).

CONCLUSION

These novel data offer a controlled demonstration for the behavior of jitter (local) %, RAP %, shimmer (local) %, APQ3 %, and HNR (dB) when varying fo, SST, and VE in synthesized tones. Since humans will vary in all of these aspects in spoken language and vowel phonation, researchers should take potential resonance-harmonics type effects into account when comparing intersubject or preintervention and postintervention data using these measures.

It Sounds like It Feels: Preliminary Exploration of an Aeroacoustic Diagnostic Protocol for Singers

To date, no established protocol exists for measuring functional voice changes in singers with subclinical singing-voice complaints. Hence, these may go undiagnosed until they progress into greater severity. This exploratory study sought to (1) determine which scale items in the self-perceptual Evaluation of Ability to Sing Easily (EASE) are associated with instrumental voice measures, and (2) construct as proof-of-concept an instrumental index related to singers' perceptions of their vocal function and health status. Eighteen classical singers were acoustically recorded in a controlled environment singing an /a/ vowel using soft phonation. Aerodynamic data were collected during a softly sung /papapapapapapa/ task with the KayPENTAX Phonatory Aerodynamic System. Using multi and univariate linear regression techniques, CPPS, vibrato jitter, vibrato shimmer, and an efficiency ratio (SPL/PSub) were included in a significant model (p < 0.001) explaining 62.4% of variance in participants' composite scores of three scale items related to vocal fatigue. The instrumental index showed a significant association (p = 0.001) with the EASE vocal fatigue subscale overall. Findings illustrate that an aeroacoustic instrumental index may be useful for monitoring functional changes in the singing voice as part of a multidimensional diagnostic approach to preventative and rehabilitative voice healthcare for professional singing-voice users.

The Role of Vibrato in Group Singing: A Systematic Review

INTRODUCTION

Arguably one of the most controversial features of the singing voice, especially in a choral context, is the phenomenon of vibrato. Numerous pedagogical articles, mostly written by experienced choral singers or directors, discuss the importance of vibrato, sharing anecdotal insights about its control (often advocating reduction) in choral blend and vocal health.

OBJECTIVES

This systematic review aims to identify the main questions posed in the empirical study of vibrato during group singing, and how they have been addressed to date through empirical investigations.

METHODS

The Preferred Reporting Items for Systematic Reviews and Meta-Analyses was employed for this review. The review team consisted of the two authors. A data extraction form was designed to capture information about the participants (including age, gender, music and singing experience), study methods, experimental procedures, outcome measures, and statistical findings.

RESULTS

Seventeen studies were included in the review and revealed that (a) relatively few empirical investigations have studied vibrato in vocal ensembles; (b) the majority focused on vibrato production rather than perception; (c) methodological approaches include Synthesis, Multi-track recordings, Stereo/Binaural recordings, and Lx/Contact recordings; and (d) the studies focused on the main themes of Adjustment, Identification, Interaction, Intonation, and Style.

CONCLUSION

With the current body of literature, it is not possible to draw general conclusions around vibrato behavior during group singing. However, the review highlights the main subareas of interest and valuable methods which have been established and through which future research can collectively shed further light on the role of vibrato in choral singing.

The Use of Vibrato in Belt and Legit Styles of Singing in Professional Female Musical-Theater Performers

OBJECTIVE

Musical theater (MT) performers are required to sing in several different styles, requiring different registration (quality) and different use of vibrato. Many measures of vibrato in MT performers are made in laboratory settings, studying a limited set of pitches, intensities, and vowels, using amateur and not well-defined professional singers. It is unclear if these observations are observed in well-known professional MT singers, during live instrumentally accompanied legit and belt performances.

STUDY DESIGN

Descriptive from a convenience sample.

METHODS

Five well-known MT performers' recordings of one legit and one belt performance were downloaded for analysis of vocal vibrato. The vocal part was extracted from the recording and each note demarcated with and without vibrato. The pitch track of each note was analyzed for average pitch, duration, the proportion of a note sung with vibrato, if present, and written to file. The pitch track (f0 and time stamps) was written to a separate file for further analysis. This analysis consisted of vibrato rate (Hz), vibrato extent (semitones), and cycle-to-cycle perturbation (jitter-local and shimmer-local).

RESULTS

The most consistent finding was that the belt performances of the five singers had lesser proportion of notes sung with vibrato than their legit performances. The next consistent finding was that during belt performances, when vibrato was used, it was for a shorter duration within a note. There was a trend for the average rate of vibrato to be slower in the belt performances, but not to a substantial degree. There was no clear difference between legit and belt performances for vibrato extent or cycle-to-cycle perturbation.

CONCLUSIONS

For these five performers, the strategy for the use of vibrato most often employed for differentiating the two singing styles was using less vibrato and when used to engage it for a shorter portion of a sung note. We believe this study offers reasonable ecological validity in how professional MT performers utilize vibrato to distinguish between belt and legit styles of singing. Vibrato rate and extent are subject to a number of factors which may not be in direct control of the singer. However, learning to sing with and without vibrato and the duration to which it is produced within a note may be a useful training strategy for students of MT.

Relationship Between Oropharyngeal Geometry and Acoustic Parameters in Singers: A Preliminary Study

OBJECTIVE

To verify possible correlations between formant and cepstral parameters and oropharyngeal geometry in singers, stratified by sex.

METHOD

Voice records and oropharyngeal measures of 31 singers - 13 females and 18 males, mean age of 28 (±5.0) years - were retrieved from a database and analyzed. The oropharyngeal geometry measures were collected with acoustic pharyngometry, and the voice records consisted of sustained vowel /Ԑ/ phonation, which were exported to Praat software and edited to obtain the formant and cepstral parameters, stratified by sex. The Pearson linear correlation test was applied to relate voice parameters to oropharyngeal geometry, at the 5% significance level; the linear regression test was used to justify the variable related to the second formant.

RESULTS

Differences between the sexes were identified only in the oral cavity length (greater in males) and pharyngeal cavity length (greater in females). There was a linear correlation between the third formant and the cepstrum in the female group. In the male group, there was a linear correlation between the cepstrum and the third and fourth formants. A positive linear correlation with up to 95% confidence was also identified between the pharyngeal cavity volume and the second formant in the female group, making it possible to estimate a regression model for the second formant (R2 = 0.70).

CONCLUSION

There are correlations between the oropharyngeal geometry and formant and cepstral parameters in relation to sex. The pharyngeal cavity volume showed the greatest correlation between females and the second formant.

Singing in different performance spaces: The effect of room acoustics on vibrato and pitch inaccuracy

Previous literature suggests that musical performers may be influenced to some extent by the acoustic environment in which they sing or play. This study investigates the influence of room acoustics on singers' voice production, by analyzing consecutive sung performances of classically trained students in five different performance spaces. The analyzed voice parameters were vibrato rate, extent, and pitch inaccuracy. Nine classically trained student-singers performed the same aria unaccompanied on a variable starting pitch that was consistent between spaces. Variance in vibrato rate and pitch inaccuracy was primarily explained by individual differences between singers. Conversely, the variance attributable to the rooms for the parameter of vibrato extent was larger compared to the variance attributable to the performers. Vibrato extent tended to increase with room clarity (C80) and was inversely associated with early decay time (EDT). Additionally, pitch inaccuracy showed a significant negative association with room support (ST_v). Singers seem to adjust their vocal production when performing in different acoustic environments. Likewise, the degree to which a singer can hear themself on stage may influence pitch accuracy.

La voz en los cantantes líricos. Protocolo para su valoración clínica y acústica

El objetivo de esta investigación es elaborar un protocolo clínico y acústico con diversas técnicas para evaluar la voz de los cantantes líricos. Se seleccionaron 18 cantantes líricos, que se consideraban sanos, clasificados como soprano, mezzosoprano, contralto, tenor, barítono y bajo. A todos se les realizó la anamnesis, el S-VHI y una serie de estudios aerodinámicos (TMF, índice s/e y cociente de fonación) y acústicos (F0, intensidad, HNR, Jitter, Shimmer, espectrograma, fonetograma y LTAS), así como una exploración clínica e instrumental estroboscópica. El 33% eran fumadores, siendo este hábito más frecuente en hombres. El S-VHI detectó 20 puntos sobre 144 posibles, puntuación relativamente alta de su grado de incapacidad. Casi la mitad obtuvieron valores fuera del rango de normalidad en el TMF, índice s/e y cociente de fonación. Las características acústicas de su voz y los rangos vocales y dinámicos estaban, en la mayoría de los casos, dentro de la normalidad. En el 55% se observó algún tipo de patología laríngea. Los cantantes deberían evitar el uso del tabaco, así como hacer revisiones frecuentes para detectar patologías laríngeas que pasan desapercibidas. Los valores aerodinámicos y acústicos muestran alteraciones con respecto a los valores normales de referencia. La presencia de vibrato y formante del cantante puede verse en el espectrograma y el LAST, así como el rango dinámico y vocal con el fonetograma. El uso del protocolo clínico y acústico proporciona importante información que completa la obtenida por el terapeuta vocal o el profesor de técnica vocal en el análisis perceptual de la voz profesional.

Listener Ratings of Male Singer Technical Ability

Perceptual judgments of singer technical ability have not been widely researched. A few studies have examined perceptions of singers versus nonsingers (Usha 2017) and evaluations of vocal beauty in the male voice (Robison 1992). The investigators used recordings of male voices singing [i] in an online survey instrument using a Likert-type scale. Listeners were divided into four groups (nonmusicians, music ensemble participants, music students, and music professionals). Listeners rated the technical ability of each singer (27 recordings) on a 6-point scale from beginning to advanced. Survey responses of the four listener groups were compared with vibrato rate, extent, and jitter of the recorded samples. We hypothesized that musical training would affect how listeners rate male singers overall, with the expectation that the most musically experienced and trained listeners' ratings would be the most severe.

Acoustic Analyses of the Singing Vibrato in Traditional Peking Opera

China's traditional Peking Opera has four standard categories of roles: Sheng, Dan, Jing, and Chou, the singing vibrato of each displaying a different auditory effect. The audio and respiratory signals were recorded for two performers of the Qing Yi role, one of the Jing role, one of the Chou role, one of the Lao Sheng role, one of the Xiao Sheng role, and one of the Lao Dan role. The recordings gained eventually consisted of 24 representative songs from six roles. The rates and extents of vibrato, fundamental frequency, and rib cage signals were analyzed. Two findings were obtained: (1) the classical opera singing vibratos of China and Western countries are acoustically different from each other; and (2) in Peking Opera, the singing vibratos of different roles show significant acoustic differences.

Automatic Assessment of Acoustic Parameters of the Singing Voice: Application to Professional Western Operatic and Jazz Singers

INTRODUCTION

The obvious perceptual differences between various singing styles like Western operatic and jazz rely on specific dissimilarities in vocal technique. The present study focuses on differences in vibrato acoustics and in singer's formant as analyzed by a novel software tool, named BioVoice, based on robust high-resolution and adaptive techniques that have proven its validity on synthetic voice signals.

MATERIAL AND METHODS

A total of 48 professional singers were investigated (29 females; 19 males; 29 Western operatic; and 19 jazz). They were asked to sing "a cappella," but with artistic expression, a well-known musical phrase from Gershwin's Porgy and Bess, in their own style: either operatic or jazz. A specific sustained note was extracted for detailed vibrato analysis. Beside rate (s(-1)) and extent (cents), duration (seconds) and regularity were computed. Two new concepts are introduced: vibrato jitter and vibrato shimmer, by analogy with the traditional jitter and shimmer of voice signals. For the singer's formant, on the same sustained tone, the ratio of the acoustic energy in formants 1-2 to the energy in formants 3, 4, and 5 was automatically computed, providing a quality ratio (QR).

RESULTS

Vibrato rates did not differ among groups. Extent was significantly larger in operatic singers, particularly females. Vibrato jitter and vibrato shimmer were significantly smaller in operatic singers. Duration of vibrato was also significantly longer in operatic singers. QR was significantly lower in male operatic singers.

CONCLUSIONS

Some vibrato characteristics (extent, regularity, and duration) very clearly differentiate the Western operatic singing style from the jazz singing style. The singer's formant is typical of male operatic singers. The new software tool is well suited to provide useful feedback in a pedagogical context.

Perception of a sung vowel as a function of frequency-modulation rate and excursion in listeners with normal hearing and hearing impairment

PURPOSE

Frequency fluctuations in human voices can usually be described as coherent frequency modulation (FM). As listeners with hearing impairment (HI listeners) are typically less sensitive to FM than listeners with normal hearing (NH listeners), this study investigated whether hearing loss affects the perception of a sung vowel based on FM cues.

METHOD

Vibrato maps were obtained in 14 NH and 12 HI listeners with different degrees of musical experience. The FM rate and FM excursion of a synthesized vowel, to which coherent FM was applied, were adjusted until a singing voice emerged.

RESULTS

In NH listeners, adding FM to the steady vowel components produced perception of a singing voice for FM rates between 4.1 and 7.5 Hz and FM excursions between 17 and 83 cents on average. In contrast, HI listeners showed substantially broader vibrato maps. Individual differences in map boundaries were, overall, not correlated with audibility or frequency selectivity at the vowel fundamental frequency, with no clear effect of musical experience.

CONCLUSION

Overall, it was shown that hearing loss affects the perception of a sung vowel based on FM-rate and FM-excursion cues, possibly due to deficits in FM detection or discrimination or to a degraded ability to follow the rate of frequency changes.

O vibrato de cantores profissionais da música gospel

Objetivo verificar as características do vibrato de cantores profissionais de acordo com o estilo da música gospel; e se o comando verbal para a realização do vibrato interfere em suas características. Métodos aprovação do CEP. Analisou-se as características espectrográficas do vibrato de 20 cantores gospel profissionais, 06 homens e 14 mulheres (média de idade: 30 anos), por meio de dois estilos gospel – adoração e pentecostal. Estruturou-se duas situações de gravação – ausência e presença de comando verbal para a realização do vibrato. Todos os participantes responderam ao item de sinais e sintomas vocais do protocolo CPV-P e realizaram avaliação laringológica. Resultado observou-se que no estilo pentecostal 95% dos participantes realizaram vibrato regular, com maior variação da amplitude, maior energia do espectro e melhor definição dos harmônicos; na adoração 100% realizaram vibrato irregular, com menor variação da amplitude, menor energia no espectro e 50% tiveram presença de harmônicos com menor definição e 50% com ausência de harmônicos. Na análise espectrográfica observou-se que, no pentecostal, houve vibrato regular em 75% dos sujeitos, maior variação da amplitude em 65%, maior energia no espectro em 55%, e presença com maior definição em 70%, tanto para situação sem comando verbal quanto para a com comando para realização de vibrato. Não houve relação entre aulas de canto, terapia fonoaudiológica e características do vibrato. Conclusão o vibrato de cantores treinados modifica conforme o estilo gospel cantado. O comando verbal para a realização do vibrato aumenta a definição de regularidade, amplitude, energia no espectro e definição dos harmônicos.