Measurements of vibrato parameters in long sustained crescendo notes as sung by ten sopranos

Two high-pitched and long sustained notes, F5 and A5, were selected from an aria found in ten commercial recordings of G Verdi's opera Aida by ten different sopranos. Both notes were sung without any instrumental accompaniment and with a crescendo. These audio examples were analyzed with regard to fundamental frequency, vibrato rate, vibrato extent, intonation and sound level, and the relationship among these parameters. The results reveal that vibrato rate differed significantly between the tones in most of the singers and confirm Prame's observations that vibrato rate tends to increase exponentially toward the end of tones. Moreover, both vibrato extent and mean F0 often varied systematically with sound level. The regularity of the vibrato tended to be greater at F5 than at A5.     

Sound pressure level and spectral balance linearity and symmetry in the messa di voce of female classical singers

The messa di voce, in its pure form a crescendo and decrescendo on one note, has been revered for centuries in classical singing, but the pedagogical assumptions of linearity and symmetry have received little critical assessment, especially across a wide fundamental frequency (F0) range. Five trained female classical singers performed a total of 318 messe di voce across their musical F0 range to identify its acoustical characteristics and the influence of F0. Sound pressure level (SPL) range was generally greater during crescendo at higher F0's and during decrescendo at lower FO's. Change in SPL during the messa di voce was predominantly nonlinear, and the shape of the SPL traces differed greatly between crescendo and decrescendo. Nonlinearity in SPL change was not related to SPL range but did show a F0 influence in decrescendo. Change in spectral balance (0-2 vs. 2-4 kHz) with respect to SPL change showed markedly more symmetry than linearity, so that changes in the mode of phonation during the messa di voce were dependent upon SPL regardless of whether the singer was in crescendo or decrescendo. Perceptual and physiological implications are discussed.     

Acoustic characteristics of vocal oscillations: Vibrato, exaggerated vibrato, trill, and trillo

Acoustic analysis was performed on recordings of 10 early music singers producing examples of vibrato, exaggerated vibrato, whole-tone trill, and trillo to obtain measures of oscillation rate, frequency extent, and jitter. Oscillation rates for vibrato, exaggerated vibrato, and trill were similar, but trillo rate was much faster. Average frequency extent of oscillation was 1 semitone (st) for vibrato, 2.21 st for exaggerated vibrato, 2.71 st for whole-tone trill, and 1.64 st for trillo. Jitter measures indicated that exaggerated vibrato had the most stable oscillations and trillo the least.     

On the use of the maximum likelihood estimation for analysis of vibrato tones

Characteristics of frequency vibrato are usually explained by the frequency center, rate, and extent. For analysis of vibrato tones, we apply the maximum likelihood estimation to the enhanced fundamental frequency track obtained from a short-time Fourier transform. We have also suggested the values of the parameters in the estimation and the averaging process to reduce the estimation error. Experiments show that the proposed method can be used for accurate and reliable analysis of vibrato tones.     

Vibrato Rate Adjustment

The goal of the present study was to document the acoustic changes that occur as singers attempt to increase or decrease their vibrato rate to match target stimuli. Eight advanced singing students produced vowels with vibrato in three registers, both naturally and while attempting to match faster or slower rate stimuli. Slower rates were associated with lower intensity and less steady vibrato. Faster rates involved increased vibrato extent in the chest register and increased intensity in the head register. Singers whose spontaneous vibrato rates were naturally either slower or faster tended to also be relatively slower or faster when matching target rates. This ability to modify rate may have beneficial effects on the artistic quality of the voice for performance.     

Comparing historical and contemporary opera singers with historical and contemporary Jewish cantors

This study is an attempt to ascertain if singers from different traditions and milieus follow similar aesthetic trends regardless of training and/or background. Cantors who sang the Jewish synagogue liturgy during the Golden Age of cantorial singing prior to World War II came from Eastern and Central Europe. For the most part, they were not trained in the classical Western opera tradition. They received training from choir leaders and other cantors and the training was primarily in the modes of synagogue chant. Cantors today receive the same kinds of training that opera singers receive, often from the same teachers. Four groups of singers, consisting of four singers in each group, were utilized in this study. The four groups are: historical opera singers, contemporary opera singers, historical cantors, and contemporary cantors. The historical opera singer recordings date from as early as 1909 to as late as 1939. It was not possible to determine the dates of the historical cantor recordings. However, the four cantors chosen for this group were active only to the 1940s. Contemporary samples were taken from CDs and/or live recordings and all the singers from the contemporary groups are either still active or were active in the 1960s through the 1980s and all of them are considered to be premier-level singers in their respective areas. The variables analyzed were: vibrato pulse rate, frequency variation of the vibrato pulse above and below the mean sustained sung frequency in percent, the mean amplitude variation of the amplitude vibrato pulse above and below the mean sustained amplitude in percent and the fast Fourier transform (FFT) power spectrum of the sustained samples. Results indicate that most of the significant differences were found between eras and not between groups within a time period.     

Messa di voce: an investigation of the symmetry of crescendo and decrescendo in a singing exercise.

A classical vocal exercise called "messa di voce" (Italian for "placing the voice") was used to study the symmetry of intensity increase and decrease in six trained singers. Ideally, the exercise is performed as a symmetric triangle, a linear increase in loudness, followed by a linear decrease. Given that some physiologic variables, like lung volume, undergo unidirectional change rather than a symmetric reversal, there is reason to believe that symmetries may not exist. It was found that highly trained singers who use large SPL ranges tend to abbreviate the decrescendo phase in comparison with the crescendo phase. In a few other cases, a plateau in SPL is reached, but an increase in loudness may still be perceived on the basis of a stronger vibrato or changes in timbre.     

Inter- and intrasubject changes in vibrato: Perceptual and acoustic aspects

Recent papers by Rothman and Timberlake (1), Rothman (2), Rothman and Arroyo (3), and Keidar, Titze, and Timberlake (4) have focused on the pulse rate, frequency extent, and amplitude extent of vibrato. Some of the emphases of these papers were attempts to clarify the acoustic and perceptual correlates of vibrato, tremolo, and wobble. Rothman and Arroyo (3) speculated that the shape of the frequency variation waveform may be indicative of vocal problems. In order to verify this, we examined recorded segments of sung samples produced by different singers and samples taken from the early and late stages of singers' careers. Some singers had a relatively short career before exhibiting vocal problems. Others had relatively long careers before showing evidence of vocal decline. Many, but not all, of the singers' late career recordings represent examples generally acknowledged to evidence vocal problems/decline. Each sample was digitized at a sampling frequency of 10 kHz, stored, and analyzed using programs reported on by Rothman and Arroyo (3). Data analysis revealed that some parameters can distinguish between good and bad vibrato despite the variance in listener judgments. Furthermore, evidence of vocal decline is not always due to changes in singers' vibrato.     

The relationship between measured vibrato characteristics and perception in Western operatic singing

This study examined the association between acoustic and perceptual data related to vibrato in Western operatic singing using recordings of performances by internationally famous opera singers. Three related studies were conducted. Study 1 used commercial recordings of the same five singers and the same cadenza examined by Siegwart and Scherer(1), measured vibrato rate and extent in each singer's performance of the cadenza and tested possible associations between these vibrato attributes and judges' preference for singers. Studies 2 and 3, using recordings of different internationally famous singers and a different cadenza, measured vibrato onset, rate, and extent in each singer's performance of the cadenza, required judges to rank the singers in order of personal preference, to identify the emotion expressed, and to assess the degree of success in communicating emotion achieved by the singer. The findings showed that the perception of the singers' vibrato did not always agree with acoustic measurements. However, a comparison of the acoustic measurements with the preference and emotion judgments suggest that some elements of vibrato may affect listeners' perception of the voice, their preference for a particular singer, and assist the communication of emotion between singer and audience.     

Acoustical Comparison Between Samples of Good and Poor Vibrato in Singers

The purpose of this research was to analyze samples of frequency vibrato taken from recordings of eight different singers, which were classified as examples of good or poor singing. The samples were analyzed by a software package, which makes use of the linear prediction coding (LPC) method to determine the time varying rate and extent of the frequency vibrato wave. Four parameters, which relate to the periodicity of the samples, were extracted from the time varying rate and extent and investigated in order to verify or reject the hypothesis that the best vibrato samples were the most symmetric ones. Ten samples per singer were analyzed, 5 good and 5 poor, for a total of 80 samples. The results show that the samples judged as good were the most periodic ones.     

Videofluoroscopic and Laryngoscopic Evaluation of the Upper Airway and Larynx of Professional Bassoon Players

The bassoon is a demanding double-reed woodwind instrument requiring exquisite control of airflow and air pressure to the reed to produce desired tonal characteristics. Little information is available from direct visualization of the vocal tract and larynx of the bassoonist while playing. Of particular interest is the mechanism(s) of vibrato. This study was undertaken to understand more fully the mechanics of the upper airway in bassoonists during music production. Four adult bassoon players served as subjects. Three players were studied with both sound-synchronized videofluoroscopy and fiber-optic nasal endoscopy. The other subject was studied only by fiber-optic endoscopy. All subjects were evaluated while playing various scales and standard passages common in music pedagogy. The results from this study revealed several findings on the mechanics of upper airway activity during playing: (1) firm velopharyngeal closure was a prerequisite for maximal containment of air pressure and regulation of airflow in the oropharyngeal regions; (2) changes in the pitch and intensity were associated with differential expansion of the pharynx; (3) tongue activity was notable because of its shaping the size and shape of the airway, its role in regulating airflow to the reed, and its contributions to conditioning airflow in vibrato; and (4) slight vocal fold displacements from subglottal airflow and epiglottic movements from tongue base activity contributed to airway changes during vibrato. These seemed to further condition subglottal pressure trains derived primarily from expiration.     

Acoustical measurements of expression devices in pipe organs

In this investigation, three different swell systems known in pipe organs, the swell box, the crescendo wheel, and the historic wind swell were measured and compared to each other. The dynamic range of the crescendo wheel was found to be most effective, and for frequencies near 2 kHz the increase in sound pressure level could be up to 50 dB between the softest and the loudest adjustment. The maximum dynamic range for the wind swell and the swell box were found to be 10-20 dB in the same frequency range. With its step-wise crescendo procedure, the crescendo wheel simulates the type of orchestra crescendo which is reached by successively adding further musical instruments. In contrast, the swell box and the wind swell produce a crescendo effect similar to the crescendo in which individual musical instruments perform a dynamic movement. This type of crescendo requires a continuous level increase but allows a smaller dynamic range. The disappearance of the wind swell is not surprising because it offers no advantage over the swell box, while being restricted to stops with free reeds.     

A study of repeated measures of softest and loudest phonations

One common way to describe one's voice in an objective way is to measure the sound levels of the softest (pianissimo) and loudest possible (fortissimo) phonations at given pitches (voice range profile measurement). However, the reliability of the measurement has not been thoroughly investigated. The aim of the present study was to describe the repeatability and reproducibility of the sound level measurement in statistical terms, focusing on five target frequencies within the estimated speaking pitch range. Ten healthy female university students volunteered as test subjects. The voice range profiles within the speaking pitch range were defined 10 times in succession and in five sample sessions between 45-minute-long oral readings. Our study followed the ideas of the Gage repeatability and reproducibility design. The results showed that the method used was reliable in fortissimo phonations at four of the measured frequencies. Better reliability can be achieved by measuring three successive phonations at each pitch prior to the next target tone.     

Acoustic variability in vibrato and its perceptual significance

Historically, studies of vocal vibrato have concentrated on pulse rate as being a primary factor in determining whether a given vocal movement is a good or bad vibrato or a tremolo or wobble. More recently, investigators have been studying the extent of frequency variation and amplitude variation around their respective means in order to determine their influence on the perception of vibrato. The present study is an additional attempt to understand the three parameters comprising vibrato, their interrelationship, and their relationship to perception. Samples of sustained sung tones were obtained primarily from recordings. The samples were digitized using a 16-bit A/D converter at a sampling frequency of 10 kHz. Each digitized sample was converted to a useful format for marking purposes in order to derive information on vibrato pulse rate, the mean frequency of the tone, the semitone deviation around the mean, percent frequency deviation and percent amplitude variation around the mean amplitude. Data presentation utilizes representative samples of good vibrato, tremolo and wobble and describes differences in waveforms which may impact on perception.     

The role of auditory feedback in sustaining vocal vibrato

Vocal vibrato and tremor are characterized by oscillations in voice fundamental frequency (F0). These oscillations may be sustained by a control loop within the auditory system. One component of the control loop is the pitch-shift reflex (PSR). The PSR is a closed loop negative feedback reflex that is triggered in response to discrepancies between intended and perceived pitch with a latency of approximately 100 ms. Consecutive compensatory reflexive responses lead to oscillations in pitch every approximately 200 ms, resulting in approximately 5-Hz modulation of F0. Pitch-shift reflexes were elicited experimentally in six subjects while they sustained /u/ vowels at a comfortable pitch and loudness. Auditory feedback was sinusoidally modulated at discrete integer frequencies (1 to 10 Hz) with +/- 25 cents amplitude. Modulated auditory feedback induced oscillations in voice F0 output of all subjects at rates consistent with vocal vibrato and tremor. Transfer functions revealed peak gains at 4 to 7 Hz in all subjects, with an average peak gain at 5 Hz. These gains occurred in the modulation frequency region where the voice output and auditory feedback signals were in phase. A control loop in the auditory system may sustain vocal vibrato and tremorlike oscillations in voice F0.     

Vibrato of saxophones

Several alto saxophone players' vibratos have been recorded. The signals are analyzed using time-frequency methods in order to estimate the frequency modulation (vibrato rate) and the amplitude modulation (vibrato extent) of each vibrato sample. Some parameters are derived from the results in order to separate the two ways of vibrato playing: vibrato "à la machoire" and vibrato "sur l'air." Moreover, time domain simulations of single-reed instrument vibratos are created. The model is controlled by two parameters: the mouth overpressure and a parameter characterizing the reed-mouthpiece system. Preliminary comments and comparisons between the simulated vibratos and recorded vibratos results are made.     

The time-frequency characteristics of violin vibrato: modal distribution analysis and synthesis

A high-resolution time-frequency distribution, the modal distribution, is applied to the study of violin vibrato. The analysis indicates that the frequency modulation induced by the motion of the stopped finger on the string is accompanied by a significant amplitude variation in each partial of that note. Amplitude and frequency estimates for each partial are extracted from the modal distribution of ten pitches that span the range of the violin instrument. The frequency modulation is well-represented by a single sinusoid with a mean rate of 5.9 Hz and a mean excursion of +/- 15.2 cents. A spectral decomposition of the amplitude envelopes of the partials shows that the peaks lie primarily at integer multiples of the vibrato rate. These amplitude and frequency estimates are used in an additive synthesis model to generate synthetic replicates of violin vibrato. Simple approximations to these estimates are created, and synthesized sounds using these are evaluated perceptually by seven subjects using discrimination, nonmetric multidimensional scaling (MDS), and sound quality scoring tasks. It is found that the absence of frequency modulation has little effect on the perceptual response to violin vibrato, while the absence of amplitude modulation causes marked changes in both sound quality and MDS results. Low-order spectral decompositions of the amplitude and frequency estimates also occupy the same perceptual space as the original recording for a subset of the pitches studied.     

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.     

Modal Distribution Analysis, Synthesis, and Perception of a Soprano''s Sung Vowels

A high-resolution time-frequency analysis technique, the modal distribution, is applied to sung vowels from a soprano singer. Parameters are estimated for each partial component of notes analyzed with the modal distribution. These estimates are used in an additive synthesis model to generate replicates of the original recording, using a series of time-varying sinusoids. Additionally, a source-filter model is applied to create synthetic signals, where pitch- and vowel-specific filters and driving functions are constructed from the amplitude and frequency estimates obtained. Different driving functions, which sample the range of this singer's rate and excursion variation, are transposed and filtered to create synthetic signals. The perceptual salience of the different rates and excursions is then determined via a paired-comparison listening experiment. It is found that listeners are sensitive to small variations in both average vibrato rate and average vibrato excursion. However, the perceived amount of vibrato excursion varies somewhat depending upon the pitch at which the vibrato is “played” synthetically. Finally, the naturalness and sound quality of these synthetic examples is determined through both paired-comparison and single-note sound quality scaling listening experiments.