An electroglottographic study of vocal vibrato

This study investigated vocal vibrato in trained singers through the use of electroglottography (EGG). Ten adult trained singers (7 women, 3 men) were each required to produce four singing tasks. The tasks involved the production of /a/ during an ascending interval of a third in both chest and falsetto registers, once with and once without vibrato. Audio and EGG output during these tasks were directly digitized for subsequent analysis. Results pertaining to changes in the EGG waveform as a function of the singer's gender, the vocal register and the vibrato condition are discussed. A major finding was the apparent absence of consistent, distinctive differentiation in the EGG waveforms when comparing the vibrato and vibrato-inhibited conditions for the majority of subjects. Possible explanations for the majority findings, as well as comment on the feasibility of the EGG for investigating vocal vibrato, are discussed.     

The effects of crescendo on vocal vibrato

The purpose of this research was to investigate the effects of crescendo and decrescendo on the width of vocal vibrato. A second interest was whether the frequency at which the crescendo or decrescendo occurred would be a factor. Nine singers each produced nine phonations. The first set of three phonations was crescendo from pp to ff at low, medium, and high frequency. The second set of three was decrescendo from ff to pp at the three frequencies and the third set was from pp to ff to pp at each frequency. The vibrato width during each phonation was measured via a Kay Visipitch. The results generally indicated that vibrato width increased with increasing crescendo. With decrescendo, however, the vibrato width tended to remain constant even though the intensity was decreasing. The greatest vibrato width occurred at the middle frequencies.     

Vibrato and pitch transitions

There are at least two timing variables to be considered in vocal music performance. The first is the note changes associated with the meter signature (4/4, 2/4, etc.) and the second is the vibrato rate of the performer. Because the probability is not great that these two temporal variables will always be in perfect synchrony, it was the purpose of this investigation to determine what singers do when these two timing variables come into conflict during singing. Six singers recorded a series of alternating upward and downward interval shifts of a third while singing whole notes, half notes, quarter notes and eighth notes. The same notes were then recorded with intervals of a fifth. The recorded samples were converted to a visual trace and examined for interactions between vibrato and meter. Analysis of the tracings indicated that, in the majority of the cases, the singers would alter their vibrato in order to adhere to the timing of the musical line.     

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.     

Vocal warm-up produces acoustic change in singers' vibrato rate

Vibrato rate and vibrato extent were acoustically assessed in 12 classically trained female singers before and after 25 minutes of vocal warm-up exercises. Vocal warm-up produced three notable changes in vibrato rate: (1)?more regularity in the cyclic undulations comprising the vibrato rate of a note, (2) more stability in mean vibrato rates from one sustained note to the next, and (3) a moderating of excessively fast and excessively slow mean vibrato rates. No significant change was found for vibrato extent. The findings indicate that vocal warm-up may regulate vibrato rate. Thus tone quality, which is strongly linked to vibrato characteristics, may undergo positive change as a result of vocal warm-up.     

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.     

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.     

Perceptual and acoustic study of professionally trained versus untrained voices

Acoustic and perceptual analyses were completed to determine the effect of vocal training on professional singers when speaking and singing. Twenty professional singers and 20 nonsingers, acting as the control, were recorded while sustaining a vowel, reading a modified Rainbow Passage, and singing "America the Beautiful." Acoustic measures included fundamental frequency, duration, percent jitter, percent shimmer, noise-to-harmonic ratio, and determination of the presence or absence of both vibrato and the singer's formant. Results indicated that, whereas certain acoustic parameters differentiated singers from nonsingers within sex, no consistently significant trends were found across males and females for either speaking or singing. The most consistent differences were the presence or absence of the singer's vibrato and formant in the singers versus the nonsingers, respectively. Perceptual analysis indicated that singers could be correctly identified with greater frequency than by chance alone from their singing, but not their speaking utterances.     

Acoustic properties of straight tone, vibrato, trill, and trillo

Recordings were made of four internationally acclaimed early music singers (two women, two men) as they sustained phonation at target frequencies while producing the vocal ornaments straight tone, vibrato, trill, and trillo. Recordings were analyzed for the presence and amount of fundamental frequency oscillation and the frequency location of the vocal ornament performed with respect to the target tone. Results showed great variability between singers in all measured parameters.     

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.     

The effects of preventive vocal hygiene education on the vocal hygiene habits and perceptual vocal characteristics of training singers

The purpose of the present study was to determine the effects of vocal hygiene education on the vocal hygiene behaviors and perceptual vocal characteristics of untrained singers. Eleven adult untrained singers served as subjects. They attended four 1-hour class sessions on vocal hygiene, including anatomy and physiology of the phonatory mechanism, vocally abusive behaviors, voice disorders commonly seen in singers, and measures to prevent voice disorders. Pre- and postinstruction surveys were used to record subjects' vocal abuses and their perceptions of their speaking and singing voice. They also rated their perceived value of vocal hygiene education. Results revealed minimal changes in vocal hygiene behaviors and perceptual voice characteristics. The subjects did report a high degree of benefit and learning, however.     

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.     

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.     

Effects of Professional Singing Education on Vocal Vibrato—A Longitudinal Study

Vocal vibrato is regarded as one of the essential characteristics of voice quality in classical singing. Professional singers seem to develop vibrato automatically, without actively striving to acquire it. In this longitudinal investigation, the vocal vibrato of 22 singing students was examined at the beginning of and after 3 years of professional singing education. Subjects sang an ascending-descending triad pattern in slow tempo on vowel [a:] at a comfortable pitch level twice at soft (piano) and twice at medium (mezzoforte) loudness. The top note of the triad pattern was sustained for approximately 5s. The mean and the standard deviation (SD) of the vibrato rate were measured for this note. Results revealed that after 3 years of training, voices with vibrato slower than 5.2 Hz were found to have a faster vibrato, and voices with vibrato faster than 5.8 Hz were found to have a slower vibrato. Standard deviation of vibrato rate was higher in soft than in medium loudness, particularly before the education. Also high values of SD of vibrato rate, exceeding 0.65 Hz, had decreased after the education. These findings confirm that vibrato characteristics can be affected by singing education.     

Membranous and cartilaginous vocal fold adduction in singing

While vocal fold adduction is an important parameter in speech, relatively little has been known on the adjustment of the vocal fold adduction in singing. This study investigates the possibility of separate adjustments of cartilaginous and membranous vocal fold adduction in singing. Six female and seven male subjects, singers and non-singers, were asked to imitate an instructor in producing four phonation types: "aBducted falsetto" (FaB), "aDducted falsetto" (FaD), "aBducted Chest" (CaB), and "aDducted Chest" (CaD). The phonations were evaluated using videostroboscopy, videokymography (VKG), electroglottography (EGG), and audio recordings. All the subjects showed less posterior (cartilaginous) vocal fold adduction in phonation types FaB and CaB than in FaD and CaD, and less membranous vocal fold adduction (smaller closed quotient) in FaB and FaD than in CaB and CaD. The findings indicate that the exercises enabled the singers to separately manipulate (a) cartilaginous adduction and (b) membranous medialization of the glottis though vocal fold bulging. Membranous adduction (monitored via videokymographic closed quotient) was influenced by both membranous medialization and cartilaginous adduction. Individual control over these types of vocal fold adjustments allows singers to create different vocal timbres.     

Toward the quantification of vocal efficiency

Quantifiable aspects of vocal fold vibration may be inferred by means of the electrolaryngograph. Changes in inferred vocal fold closed quotient are considered as a possible correlate of acoustic efficiency variation; automatic measures of closed quotient compare favorably with results obtained from inverse filtering of the speech pressure waveform. This article describes closed quotient measures based on electrolaryngographic analysis of 18 trained and untrained men singers, and results show a significant difference in mean vocal fold closed quotient between trained and untrained singers.     

Comparison of young adult singers and nonsingers with vocal nodules

Comparisons were made between 10 singers and 10 nonsingers with vocal nodules and two control groups of normals, 10 singers and 10 nonsingers, on a wide range of acoustic, aerodynamic, psychoacoustic, and videostroboscopic measures. Results showed significant differences between the normals and those with nodules as well as differences between the singers and nonsingers. The singers with nodules had smaller nodules, less impairment of vibratory function, and less severe vocal symptoms than their nonsinging counterparts. The singing normals were found to be superior to the nonsinging normals on acoustic measures including jitter, shimmer, and signal-to-noise ratio. In addition, the singers, even in the presence of nodules, had superior maximum performance skills than their nonsinging counterparts.     

Reflux and vocal disorders in singers with bulimia

Dysphonia associated with bulimia has been described in the literature associated with vocal fold edema and polypoid changes. Laryngopharyngeal reflux (LPR) has been documented to cause reflux vocal fold pathology including edema and polypoid changes. We studied eight singers with bulimia and documented vocal fold pathology, including edema, posterior commissure hypertrophy, ventricular obliteration, and telangiectasia. Reflux was demonstrated in all eight. The results of this study showed that LPR may be a contributing factor to vocal disorders in singers with bulimia.     

Analysis of vocal tract parameters in parkinsonian speech

A method for the analysis of vocal tract parameters is developed, aimed to perform quantitative analysis of rigidity from speech signals of Parkinsonian patients. The cross-sectional area function of the vocal tract is calculated using pitch synchronous autoregressive moving average (ARMA) analysis. The changes in Parkinsonian subjects of the cross-sectional area during the utterance of sustained sounds are attributed to both Parkinsonian tremor and rigidity. In order to isolate the effects of the rigidity on the vocal tract from those of the tremor, an adaptive tremor cancellation (ATC) algorithm is developed, based on the correlation of tremor signals extracted from different locations of the speech production system.     

What happens during vocal warm-up?

Most singers prefer to warm up their voices before performing. Although the subjective effect is often considerable, the underlying physiological effects are largely unknown. Because warm-up tends to increase blood flow in muscles, it seems likely that vocal warm-up might induce decreased viscosity in the vocal folds. According to the theory of vocal-fold vibration, such a decrease should lead to a lower phonation threshold pressure. In this investigation the effect of vocal warm-up on the phonation threshold pressure was examined in a group of male and female singers. The effect varied considerably between subjects, presumably because the vocal-fold viscosity was not a dominating factor for the phonation-threshold pressure.