Vibrato Production Research Articles

Vocal Vibrato Characteristics in Historical and Contemporary Opera, Operetta, and Schlager

Vibrato is a core aesthetic element in singing. It varies considerably by both genre and era. Though studied extensively in Western classical singing over the years, there is a dearth of studies on vibrato in contemporary commercial music. In addressing this research gap, the objective of this study was to find and investigate common crossover song material from the opera, operetta, and Schlager singing styles from the historical early 20th to the contemporary 21st century epochs. A total of 51 commercial recordings of two songs, "Es muss was Wunderbares sein" by Ralph Benatzky, and "Die ganze Welt ist himmelblau" by Robert Stolz, from "The White Horse Inn" ("Im weißen Rößl") were collected from opera, operetta, and Schlager singers. Each sample was annotated using Praat and analyzed in a custom Matlab- and Python-based algorithmic approach of singing voice separation and sine wave fitting novel to vibrato research. With respect to vibrato rate and extent, the three most notable findings were that (1) fo and vibrato were inherently connected; (2) Schlager, as a historical aesthetic category, has unique vibrato characteristics, with higher overall rate and lower overall extent; and (3) fo and vibrato extent varied over time based on the historical or contemporary recording year for each genre. Though these results should be interpreted with caution due to the limited sample size, conducting such acoustical analysis is relevant for voice pedagogy. This study sheds light on the complexity of vocal vibrato production physiology and acoustics while providing insight into various aesthetic choices when performing music of different genres and stylistic time periods. In the age of crossover singing training and commercially available recordings, this investigation reveals important distinctions regarding vocal vibrato across genres and eras that bear beneficial implications for singers and teachers of singing.

Simulation of acoustic effects of postural laryngeal oscillatory movement during vocalization

This paper addresses the contributions of low-frequency postural laryngeal kinematics to frequency and amplitude modulations of the vocal output signal. A one-dimensional Navier–Stokes solution for fluid transport and wave propagation is used along with a laryngeal source model to simulate voice production. Vocal fold adduction and vertical laryngeal posture are modulated sinusoidally at 2–10 Hz with various amplitudes to approximate kinematic phenomena observed with MRI during production of vocal vibrato and voice tremor. The acoustic modulations are quantified in terms of formant (resonance) and fundamental frequency shifts in the radiated output signal from the mouth. Postural oscillation of the larynx is a common kinematic component of vocal tremor, although less documented during production of vibrato.

The Effects of Masked and Delayed Auditory Feedback on Fundamental Frequency Modulation in Vocal Vibrato

Although relatively precise control over the extent and rate of fundamental frequency (fo) modulation may be needed for optimal production of vibrato, the role of auditory feedback in controlling vibrato is not well understood. Previous studies altered the gain and timing of auditory feedback in singers producing vibrato and showed inconsistent effects on the extent and rate of fo modulation, which may have been related to small sample sizes or limited analyses. Therefore, the purpose of this study was to further investigate whether the gain or timing of auditory feedback impacts control of vibrato in a larger sample of speakers and with advanced statistical analyses. Ten classically-trained singers produced sustained vowels with vibrato while their auditory feedback was masked with pink noise or multi-talker babble to reduce the gain of their auditory feedback and while their auditory feedback was delayed by about 200 or 300 milliseconds to alter the timing of their auditory feedback. Acoustical analyses measured changes in the extent and rate of fo modulation in the masked and delayed trials relative to control trials. Bayesian modeling was used to analyze the effects of noise-masked, babble-masked, and delayed auditory feedback on the extent and rate of fo modulation. There was compelling evidence that noise masking increased the extent of fo modulation, and babble masking increased the variability in the rate of fo modulation (ie, jitter of fo modulation). Masked auditory feedback did not affect the average rate of fo modulation. Delayed auditory feedback did not affect the extent, rate, or jitter of fo modulation. The current study demonstrated that reducing the gain of the auditory feedback with noise masking increased the extent of fo modulation but did not affect the average rate of fo modulation in classically-trained singers producing vibrato. Reducing the gain of the auditory feedback with babble masking and altering the timing of auditory feedback with imposed delays did not affect the average extent or rate of fo modulation. However, babble masking increased the jitter of fo modulation rate, which suggests that modulated auditory feedback may affect the periodicity of fo modulation from one modulation cycle to the next. These findings clarify the role of auditory feedback in controlling vibrato and may inform the current reflex-resonance models of vibrato.

Auditory-Motor Control of Fundamental Frequency in Vocal Vibrato

The purpose of this study was to investigate how classically trained singers use their auditory feedback to control fundamental frequency (fo) during production of vocal vibrato. Two main questions were addressed: (1) Do singers produce reflexive foresponses to sudden perturbation of the fo of their auditory feedback during production of vibrato indicative of feedback control? (2) Do singers produce adaptive foresponses to repeated perturbation of the fo of their auditory feedback during production of vibrato indicative of feedback and feedforward control? In addition, one methodological question was addressed to determine if adaptive fo responses were more precisely assessed with or without an auditory cue for fo during the repeated fo perturbation paradigm. Ten classically trained singers produced sustained vowels with vibrato while the fo and harmonics of their auditory feedback were suddenly perturbed by 100 cents to assess reflexive control or repeatedly perturbed by 100 cents to assess adaptive control. Half of the participants completed the repeated perturbation experiment with an auditory cue for fo, and the other half completed the experiment without an auditory cue for fo. Acoustical analyses measured changes in mean fo in response to the auditory feedback perturbations. On average, participants produced compensatory responses to both sudden and repeated perturbation of the fo of their auditory feedback. The magnitude of the responses to repeated perturbations was larger than the responses to sudden perturbations. Responses were also larger in the cued, repeated fo perturbation experiment than in the uncued, repeated fo perturbation experiment. These findings indicate that classically-trained singers use both feedforward and feedback mechanisms to control their average fo during production of vibrato. When compared to prior studies of singers producing a steady voice, the reflexive fo responses were larger in the current study, which may indicate that the feedback control system is engaged more during production of vibrato.

Airflow Vibrato: Dependence on Pitch and Loudness

ObjectiveTo describe the airflow vibrato characteristics at various pitches and loudness levels during vocal vibrato production. MethodThis descriptive case series research design included four subjects: 1 baritone, 1 tenor, and 2 sopranos. The extent and rate of airflow vibrato and fundamental frequency vibrato were measured by analyzing /pa:pa:pa:p/ strings with at least 3-4 cycles of vibrato during the vowels. Comparison was made within and between the subjects at different pitches and loudness levels. ResultAirflow vibrato was quite evident for all subjects. Mean airflow vibrato extents were larger in female than male singers. Increase in airflow vibrato extent was observed with increase in pitch, and it was statistically significant when comparison was made within each subject, within males (for P2, M = 74.55 cc/s, S.D = 27.44 cc/s, p < 0.01), within females (for P2, M = 94.36 cc/s, S.D = 24.13 cc/s, p< 0.01), and between males & females (for P1 in females, M = 46.96 cc/s, S.D = 16.16 cc/s, p < 0.003; for P2 in females, M = 94.365 cc/c, S.D = 24.13 cc/s, p < 0.02). Statistically significant increase in airflow vibrato extent was observed between males and females only at the highest loudness level (for females, M = 81.77 cc/s, S.D = 23.80 cc/s, p < 0.0001). The range of phase difference between them was 34°-197°, and most of the time, airflow vibrato lead F0 vibrato. EGG values were also reported. ConclusionThis study shows that the characteristics of airflow vibrato are similar to F0 vibrato; i.e., airflow vibrato also has extent, rate, regularity, and waveform complexity. However, airflow vibrato waveforms were seen to be more complex in waveshape than F0 vibrato waveforms. Studies on the sources of airflow vibrato are necessary.

Blend in Singing Ensemble Performance: Vibrato Production in a Vocal Quartet

"Blend" is a defining characteristic of good vocal ensemble performance. To achieve this, directors often consider vibrato as a feature to be controlled and consequently restrict its use. Analysis of individual voices in ensemble situations presents several challenges, including the isolation of voices for analysis from recordings. This study considers vibrato production as a feature that contributes to blend through an ecological study of a vocal quartet. A vocal ensemble was recorded using head-worn microphones and electrolaryngograph electrodes to enable fundamental frequency analysis of the individual voices. The same four-part material was recorded over several weeks of rehearsal to allow analysis of conscious and subconscious changes to vibrato production over time. Alongside the recording of their rehearsal discussions, singers were also asked for opinions on vibrato production in connection with blend. The results indicate that vibrato is adjusted to some extent by individual singers to improve blend, with some instances of synchrony between voice parts. Some conscious alterations to vibrato were made to improve blend; however, these are not always evident in the data, suggesting that singers' own perceptions of their performance may be influenced by other factors. These findings indicate a need for further studies of vibrato as a feature of blend, particularly in terms of the synergies between expectation and actual production, and potential synchronicity between singers; increased understanding of vibrato in an ensemble setting will lead to more efficient rehearsal techniques and vocal training, and could prevent vocal misuse leading to pathology in the future.

Vibrato rate variability in three professional singing styles: Opera, rock, and Brazilian country

Vibrato is one of the most expressive aesthetic characteristics of singing voice. Indicative of good voice quality is typical of lyrical singing but it is also found in others styles of popular music. Acoustically, vibrato is defined as a long-term periodic modulation of the fundamental frequency. It occurs as a result of the laryngeal muscular system and is comprised of three main parameters: rate, extent, and amplitude variation. The main controversy refers to the physiological mechanism of vibrato production, specifically concerning its neurological conscious control, as well as the intra-subject variability of its acoustic parameters. In this study, we compare the characteristics related to vibrato rate (VR), assessing 423 emissions, from recorded samples, produced by 15 professional singers, publicly and artistically acclaimed in occidental culture, to represent three music styles: opera, rock and Brazilian country (sertanejo). We analyzed the samples through GRAM 5.01 and found that the VR was kept constant intra-subject, independently of the singing style. The mean values for the VR for opera and Brazilian country singers were higher 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.

Entrenamiento del vibrato en cantantes

TEMA: El vibrato de la voz es uno de los rasgos acústicos, técnicos y estilísticos más importantes en la caracterización de la cualidad de la voz en cantantes clásicos. Técnicamente, vibrato es una pulsación del tono, usualmente acompañada con pulsaciones sincrónicas de intensidad y timbre. El vibrato puede ser descrito acústicamente por el rate, extent y periodicidad de las modulaciones en frecuencia y modulaciones de la amplitud de la voz. El objetivo del presente artículo es mostrar y explicar un nuevo procedimiento para entrenar y corregir vibrato en cantantes. PROCEDIMIENTOS: Estudiante de canto lirico de 25 años, sexo masculino con clasificación vocal de barítono lirico, voz normal desde el punto de vista perceptual. La corrección del vibrato se realiza por medio del método "Entrenamiento rítmico del vibrato". Se produce la subdivisión rítmica de un pulso durante la emisión de una vocal con un "tempo" o velocidad constante. Posteriormente se varía la velocidad del pulso, las vocales y la melodía del ejercicio. Los parámetros acústicos del vibrato son evaluados objetivamente antes y después del entrenamiento. RESULTADOS: el paciente logró producir un vibrato con rate, extent y regularidad dentro de rangos normales. Esto se realizó de forma consciente y dirigida, utilizando actividad laríngea y abdominal en forma conjunta. La naturalidad del vibrato continuó mejorando después de finalizado el entrenamiento. CONCLUSIONES: es posible el entrenamiento y/o corrección del vibrato en forma dirigida a través de ejercicios específicos destinados a ese objetivo. El apoyo visual cumple un rol importante en los resultados obtenidos.

The Characterization of the Vibrato in Lyric and Sertanejo Singing Styles: Acoustic and Perceptual Auditory Aspects

The vibrato is one of the embellishments most frequently used in the singing voice and it can be found in different singing styles, among those, lyric and Sertanejo (Brazilian country western-like singing style). Considering these two styles, the objective of the present study was to analyze the production of vibrato in the singing voice in the lyric and sertanejo genres from an acoustic and perceptual viewpoint. Twenty male singers-10 classical (operatic) singers and 10 sertanejo singers-reportedly in perfect laryngeal health, served as subjects for this study. Digital recording of the subjects' voices was performed. For each phonation, acoustic analysis was carried out together with comparison of overtones and vibrato rate and extension measurements. The results have shown that the mean values for vibrato rate and extent in lyric singers were 4.55-6.25 Hz and 0-54-1.66 semitone, respectively, whereas for sertanejo they were 5.0-6.56 Hz and 0.54-0.95 semitone. In the spectrogram, there was regularity in terms of frequency oscillation in the lyric genre whereas in the sertanejo style there was no regularity.

Voice Production Mechanisms of Vocal Vibrato in Male Singers

Vibrato constitutes one of the most interesting features of singing voice. It has been the topic of interest of many researchers in different knowledge areas such as acoustics, physiology, and psychoacoustics. In spite of this, some basic aspects related to vibrato production still remain unclear, such as the origin of its most relevant acoustical features, (frequency and amplitude variations of the partials) or the relevance of recently identified physiological effects, such as pitch synchronous variations of the voice organ. In this paper, a novel interactive vibrato production model will be proposed in order to accomplish a realistic voice production description, in such a way that the source-tract interaction will be included in the prediction model. This will allow us to identify, from the acoustical signal, additional effects typical of vocal vibrato, such as slight pitch synchronous variations of the vocal tract response, as well as to analyze the relationship between the acoustical features of vibrato and the voice production elements

Effect of the glottal source and the vocal tract on the partials amplitude of vibrato in male voices

In this paper the production of vocal vibrato is investigated. The most relevant features of the acoustical vibrato signal, frequency and amplitude variations of the partials, will be related to the voice production features, glottal source (GS) and vocal tract response (VTR). Unlike previous related works, in this approach, the effect on the amplitude variations of the partials of each one of the above-mentioned voice production features will be identified in recordings of natural singing voice. Moreover, we will take special care of the reliability of the measurements, and, to this aim, a noninteractive vibrato production model will be also proposed in order to describe the vibrato production process and, more importantly, validate the measurements carried out in natural vibrato. Based on this study, it will be shown that during a few vibrato cycles, the glottal pulse characteristics, as well as the VTR, do not significantly change, and only the fundamental frequency of the GS varies. As a result, the pitch variations can be attributed to the GS, and these variations, along with the vocal tract filtering effect, will result in frequency and amplitude variations of the acoustic signal partials.

Modulation of fundamental frequency by laryngeal muscles during vibrato

The variations in voice fundamental frequency (F0) that occur during vibrato production may be produced, at least in part, by modulation of laryngeal muscle activity. We have quantified this relation by using a cross-correlation analysis of the changes in F0 during vibrato and the changes either in motor unit firing rate or in gross electromyographic activity from the cricothyroid (CT) and the thyroarytenoid (TA) muscles. Two trained amateur tenors provided the data. Correlations were generally quite strong (mean r for the CT was 0.72 for singer 1 and 0.50 for singer 2; mean r for the TA was 0.31 for singer 2), thus providing support for previous evidence that fundamental frequency modulation in vibrato involves active modulation of the laryngeal motoneuron pool, especially by the CT muscle. In addition, phase delays between muscle modulation and changes in fundamental frequency were substantial (averaging approximately 130 degrees for the CT and 140 degrees for the TA). This finding may help provide insight regarding the mechanisms responsible for the production of vibrato.

Electromyography and Muscle Activities in Double Bass Playing

Two electromyography (EMG) experiments related to double bass playing are described. By means of surface electrodes and synchronous recordings of finger movements on the string, it is shown in the first experiment that the production of vibrato is associated with pulsating contractions of two back muscles, the teres minor and the teres major. A failure in the coordination of the activity of these muscles was observed in a student having problems in producing a proper vibrato. The second experiment demonstrates clear effects of a small change in the holding of the instrument on muscular stress in the left and right trapezius muscles. These changes were revealed by the occurrence of different degrees of muscular force developed during playing. The pedagogical implications of these findings are discussed.

Physiologic factors in vocal vibrato production

Four adult male singers produced sustained vowel phonation beginning with straight tone and changing to vibrato or exaggerated vibrato. The EMG signal from the cricothyroid muscle (CT) and the voice signal were recorded. Analysis showed that the muscle signal changed from a relative steady-state interference pattern during straight tone production to a modulated signal during either of the vibrato productions. Furthermore, for vocalization at the same frequency, the integrated muscle signal was approximately the same for straight tone and vibrato. Variability in the timing of CT modulation and the resultant FO oscillation was extensive, suggesting that other muscles may be involved in vibrato regulation. Four adult male singers produced sustained vowel phonation beginning with straight tone and changing to vibrato or exaggerated vibrato. The EMG signal from the cricothyroid muscle (CT) and the voice signal were recorded. Analysis showed that the muscle signal changed from a relative steady-state interference pattern during straight tone production to a modulated signal during either of the vibrato productions. Furthermore, for vocalization at the same frequency, the integrated muscle signal was approximately the same for straight tone and vibrato. Variability in the timing of CT modulation and the resultant FO oscillation was extensive, suggesting that other muscles may be involved in vibrato regulation.

Relevant factors in modeling laryngeally controlled vocal vibrato

Rhythmic frequency oscillations that characterize vocal vibrato are produced by either of two mechanisms. One involves driving the system with respiratory pulses and the other by intrinsic laryngeal muscle activity. In this latter mode, vibrato is most readily produced when several laryngeal aspects are in order: (1) the singer's neuromuscular system has matured beyond a childhood level; (2) a critical balance of adductory‐to‐abductory force is applied to the vocal fold margins; and (3) the larynx is positioned vertically in the airway so that excessive vertical stiffening of the mucosal lining is avoided. When these conditions are met, the intrinsic laryngeal muscle activity to produce a given pitch changes from a relatively stable interference pattern to quasiperiodic modulated muscle activity oscillating at about 5.5 to 6.0 Hz. The average value of the modulated EMG pattern equals the steady‐state EMG signal used to produce that frequency without vocal vibrato. Whether only the cricothyroid muscle or other intrinsic and/or extrinsic muscle are involved in this type of vibrato production is unknown at this time.

Mean frequency of vocal vibrato relative to target frequency

<h2>Summary</h2> Six professional singers of early and contemporary music produced sustained vowel phonations at three pitch levels beginning with straight tone leading to either vibrato or to vibrato followed by exaggerated vibrato. Mean fundamental frequency (F₀) during the two vibrato conditions was compared with the target F₀, which was measured during straight tone production. During usual vibrato production the preponderance of singers lowered their mean F₀, and a lesser number maintained the straight tone mean. Only one subject elevated mean vibrato F₀. During exaggerated vibrato phonation, there were four instances of elevated F₀, but the same number of lowered F₀ as for usual vibrato.

Physiologic factors in vocal vibrato

Vocal vibrato when produced on a sustained vowel with constant subglottal air pressure is made up principally of fundamental frequency oscillations about the target pitch. This type of phonation was studied in two professional and one amateur singer, while EMG activity was sampled from their cricothyroid muscle (CT) unilaterally. Singers initiated phonation at a designated frequency without vibrato and then changed to their customary vibrato production. Coincident with the onset of vibrato, the EMG activity from the CT changed from a relatively stable interference pattern to one of quasiperiodic bursts and attenuation. Bursts immediately preceded initiation of upward F0 for the vibrato wave while attenuation preceded downward F0 movement. Further, the average integrated EMG value over one vibrato cycle equaled the EMG level for straight tone production at the same frequency. These data provide evidence for a metering system of neuromuscular discharges that equate CT activity and F0 mean whether during production of straight tone or vibrato oscillations.

Supraglottic contribution to voice quality

Summary Although there has been continuing interest in voice quality, much of this research has focused on the vocal folds rather than the supraglottal structures. This paper reports the use of videoendoscopy for studying supraglottal participation in various singing tasks. In a preliminary study presented last year by the present authors, CT scanning was used to corroborate videoendoscopic observation. Vocal tract activities observed included variation of laryngeal height with pitch, variation of pharyngeal wall dimension with pitch and vowel, and marked supraglottic constriction with certain vocal imitations. In order to gain a better understanding of vocal training, and its effect upon vocal tract physiology, a study was designed using videoendoscopy to observe singers with significant experience and training while performing various vocal tasks. The tasks focused on the following: (1) vocal tract activity associated with pitch changes; (2) the physiology involved in the production of “cover”; (3) the structures involved in the production of vibrato; and (4) the physiology of the singer's “ring.” It would appear that videoendoscopy will become increasingly more valuable to the voice community as our understanding of vocal tract physiology improves.