Vocal Tract Configurations in Male Alto Register Functions

Purpose

Professional male altos (countertenors) mostly use a register function, which is considered to be derived from falsetto. However, the sound produced differs in professional altos compared with the modal register or falsetto of untrained voices. The aim of this study was to analyze differences of the vocal tract shapes in male alto register functions.

Material and Methods

Dynamic real-time magnetic resonance imaging of eight frames per second was used to analyze the vocal tract profile in seven professional male altos who sang on the vowel /a/, an ascending and descending scale from G3 (196 Hz) to E4 (330 Hz). The scale included their register transition from modal register to stage (counter) falsetto and naïve falsetto.

Results

Register transitions from modal register to stage falsetto were associated with increased lip opening, jaw retraction, elevation and back positioning of the tongue, pharynx narrowing, uvula elevation, drop of larynx height, and tilting of the larynx. Differences between stage and naïve falsetto were found mostly with regard to lip opening and pharynx width.

Conclusions

The differences between the vocal tract configurations might have an impact on the acoustic characteristics observed in professional male alto register functions.     

Three-dimensional vocal tract imaging and formant structure: varying vocal register, pitch, and loudness

Although advances in techniques for image acquisition and analysis have facilitated the direct measurement of three-dimensional vocal tract air space shapes associated with specific speech phonemes, little information is available with regard to changes in three-dimensional (3-D) vocal tract shape as a function of vocal register, pitch, and loudness. In this study, 3-D images of the vocal tract during falsetto and chest register phonations at various pitch and loudness conditions were obtained using electron beam computed tomography (EBCT). Detailed measurements and differences in vocal tract configuration and formant characteristics derived from the eight measured vocal tract shapes are reported.     

Relation between perceived voice register and flow glottogram parameters in males

The perception of modal and falsetto registers was analyzed in a material consisting of a total of 104 vowel sounds sung by 13 choir singers, 52 sung in modal register, and 52 in falsetto register. These vowel sounds were classified by 16 expert listeners in a forced choice test and the number of votes for modal was compared to the voice source parameters: (1) closed quotient (Q(closed)), (2) level difference between the two lowest source spectrum partials (H1-H2), (3) AC amplitude, (4) maximum flow declination rate (MFDR), and (5) normalized amplitude quotient (NAQ, AC amplitude/MFDR(*) fundamental frequency). Tones with a high value of Q(closed) and low values of H1-H2 and of NAQ were typically associated with high number of votes for modal register, and vice versa, Q(closed) showing the strongest correlation. Some singer subjects produced tones that could not be classified as either falsetto or modal register, suggesting that classification of registers is not always feasible.     

Glottal configuration associated withfundamental frequency and vocal register

Simultaneous measurements of mean airflow rate, vocal intensityand fundamental frequency were made during flexible video endoscopic recording of the vowel /i/ sustained in two vocal registers, modal and falsetto. The glottal closure patterns of four males and four females were evaluated by visually inspecting the video images. Acoustic signals were recorded and analyzed to verify the frequency and intensity criteria. Aerodynamic analysis of mean airflow rate was done via Rothenberg mask and commercial software. Incomplete glottic closure was common in both males and females. The degree of closure was significantly higher for modal samples than for falsetto samples with frequency and intensity held constant. The shape of the glottal closure did not vary with changes in the mode of phonation. As expected, the mean airflow rate increased with decreased glottal closure. The results suggest that incomplete glottic closure should be considered as a normal glottal configuration in high frequency modal and falsetto phonation. Moreover, hourglass and spindle glottal configurations may also be found in both the modal and falsetto registers of normal subjects. These results also confirm the positive relationships between degree of glottal gap and mean airflow rate. Thus, mean airflow rate may be regarded as a criterion for judging degree of glottal closure.     

Differences Among Mixed,Chest, and Falsetto Registers: A Multiparametric Study

IntroductionTypical singing registers are the chest and falsetto; however, trained singers have an additional register, namely, the mixed register. The mixed register, which is also called “mixed voice” or “mix,” is an important technique for singers, as it can help bridge from the chest voice to falsetto without noticeable voice breaks.ObjectiveThe present study aims to reveal the nature of the voice-production mechanism of the different registers (chest, mix, and falsetto) using high-speed digital imaging (HSDI), electroglottography (EGG), and acoustic and aerodynamic measurements.Study DesignCross-sectional study.MethodsAerodynamic measurements were acquired for twelve healthy singers (six men and women) during the phonation of a variety of pitches using three registers. HSDI and EGG devices were simultaneously used on three healthy singers (two men and one woman) from which an open quotient (OQ) and speed quotient (SQ) were detected. Audio signals were recorded for five sustained vowels, and a spectral analysis was conducted to determine the amplitude of each harmonic component. Furthermore, the absolute (not relative) value of the glottal volume flow was estimated by integrating data obtained from the HSDI and aerodynamic studies.ResultsFor all singers, the subglottal pressure (P_Sub) was the highest for the chest in the three registers, and the mean flow rate (MFR) was the highest for the falsetto. Conversely, the P_Sub of the mix was as low as the falsetto, and the MFR of the mix was as low as the chest. The HSDI analysis showed that the OQ differed significantly among the registers, even when the fundamental frequency was the same; the OQ of the mix was higher than that of the chest but lower than that of the falsetto. The acoustic analysis showed that, for the mix, the harmonic structure was intermediate between the chest and falsetto. The results of the glottal volume-flow analysis revealed that the maximum volume velocity was the least for the mix register at every fundamental frequency. The first and second harmonic (H1-H2) difference of the voice source spectrum was the greatest for the falsetto, then the mix, and finally, the chest.ConclusionsWe found differences in the registers in terms of the aeromechanical mechanisms and vibration patterns of the vocal folds. The mixed register proved to have a distinct voice-production mechanism, which can be differentiated from those of the chest or falsetto registers.     

Comparison of biomechanical modeling of register transitions and voice instabilities with excised larynx experiments

Voice instabilities were studied using excised human larynx experiments and biomechanical modeling. With a controlled elongation of the vocal folds, the experiments showed registers with chest-like and falsetto-like vibrations. Observed instabilities included abrupt jumps between the two registers exhibiting hysteresis, aphonic episodes, subharmonics, and chaos near the register transitions. In order to model these phenomena, a three-mass model was constructed by adding a third mass on top of the simplified two-mass model. Simulation studies showed that the three-mass model can vibrate in both chest-like and falsetto-like patterns. Variation of tension parameters which mimic activities of laryngeal muscles could induce transitions between both registers. For reduced prephonatory areas and damping constants, extended coexistence of chest and falsetto registers was found, in agreement with experimental data. Subharmonics and deterministic chaos were observed close to transitions between the registers. It is concluded that the abrupt changes between chest and falsetto registers can be understood as shifts in dominance of eigenmodes of the vocal folds.     

Laryngeal electromyographic responses to perturbations in voice pitch auditory feedback

The present study was conducted to test the hypothesis that intrinsic laryngeal muscles are involved in producing voice fundamental frequency (F(0)) responses to perturbations in voice pitch auditory feedback. Electromyography (EMG) recordings of the cricothyroid and thyroarytenoid muscles were made with hooked-wire electrodes, while subjects sustained vowel phonations at three different voice F(0) levels (conversational, high pitch in head register, and falsetto register) and received randomized pitch shifts (±100 or ±300 cents) in their voice auditory feedback. The median latencies from stimulus onset to the peak in the EMG and voice F(0) responses were 167 and 224 ms, respectively. Among the three different F(0) levels, the falsetto register produced compensatory EMG responses that occurred prior to vocal responses and increased along with rising voice F(0) responses and decreased for falling F(0) responses. For the conversational and high voice levels, the EMG response timing was more variable than in the falsetto voice, and changes in EMG activity with relevance to the vocal responses did not follow the consistent trend observed in the falsetto condition. The data from the falsetto condition suggest that both the cricothyroid and thyroarytenoid muscles are involved in generating the compensatory vocal responses to pitch-shifted voice feedback.     

Bifurcations and chaos in register transitions of excised larynx experiments

Experimental data from an excised larynx are analyzed in the light of nonlinear dynamics. The excised larynx provides an experimental framework that enables artificial control and direct observation of the vocal fold vibrations. Of particular interest in this experiment is the coexistence of two distinct vibration patterns, which closely resemble chest and falsetto registers of the human voice. Abrupt transitions between the two registers are typically accompanied by irregular vibrations. Two approaches are presented for the modeling of the excised larynx experiment; one is the nonlinear predictive modeling of the experimental time series and the other is the biomechanical modeling (three-mass model) that takes into account basic mechanisms of the vocal fold vibrations. The two approaches show that the chest and falsetto vibrations correspond to two coexisting limit cycles, which jump to each other with a change in the bifurcation parameter. Irregular vibrations observed at the register jumps are due to chaos that exists near the two limit cycles. This provides an alternative mechanism to generate chaotic vibrations in excised larynx experiment, which is different from the conventionally known mechanisms such as strong asymmetry between the left and right vocal folds or excessively high subglottal pressure.     

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.     

An investigation of the laryngeal system as the resonance source of the singer''s formant

Since its introduction, the Sundberg model of the laryngeal system as the resonance source of the singer's formant has gained wide acceptance. However, no studies directly testing this hypothesis in vivo have previously been reported. Thus, the present study was undertaken to test this hypothesis on three classically trained professional male singers. The vocal behaviors of the singer-subjects were evaluated during modal and pulse register phonation via magnetic resonance imaging, strobolaryngoscopy, and acoustic analysis. Results indicated the subjects did not achieve the laryngopharyngeal/laryngeal outlet cross-sectional area ratio requisite to the model and that the formant remained robust in pulse register phonation. It was concluded that these subjects' behaviors were not consistent with Sundberg's model and that the model was inadequate to account for the generation of the singer's formant in these three subjects.     

The perceptual nature of vocal register change

This study focuses on the perceptual nature of chest and falsetto registers as a function of various production tokens and methods of perceptual evaluation. Fifteen target tones, ranging from G#3 to A#4, were sung by a male and a female subject in the context of ascending and descending sequences on the vowels /a/ and /i/. Register transitions were elicited by setting strict constraints on production. Segments of 1-s duration were extracted from the target notes, digitized, and acoustically analyzed. These excerpts were presented to ten trained listeners in four different perceptual tasks. Identification and discrimination tasks yielded nearly identical results, suggesting that the primary registers are perceived as distinct entities. The marked change from chest to falsetto as well as the locus of the transition between these registers did not vary systematically as a function of production token or perceptual task. Mean register shift-point frequencies of the male and female subjects were perceived at 320 Hz and 353 Hz, respectively. Multidimensional scaling and hierarchical clustering analyses were utilized to capture the dimensionality and the internal structure of perceptual data sets derived from the pair-wise similarity ratings. Optimal spatial representation of these data required no more than two orthogonal dimensions, with the quality attribute represented by the dominant dimension. The representation of pitch differences was reflected only in the internal ordering of the stimuli within registers, but did not affect the perceptual discontinuity between registers.     

Formant frequency analysis of children''s spoken and sung vowels using sweeping fundamental frequency production

High-pitched productions present difficulties in formant frequency analysis due to wide harmonic spacing and poorly defined formants. As a consequence, there is little reliable data regarding children's spoken or sung vowel formants. Twenty-nine 11-year-old Swedish children were asked to produce 4 sustained spoken and sung vowels. In order to circumvent the problem of wide harmonic spacing, F₁ and F₂ measurements were taken from vowels produced with a sweeping F₀. Experienced choir singers were selected as subjects in order to minimize the larynx height adjustments associated with pitch variation in less skilled subjects. Results showed significantly higher formant frequencies for speech than for singing. Formants were consistently higher in girls than in boys suggesting longer vocal tracts in these preadolescent boys. Furthermore, formant scaling demonstrated vowel dependent differences between boys and girls suggesting non-uniform differences in male and female vocal tract dimensions. These vowel-dependent sex differences were not consistent with adult data.     

Pitch (F0) and formant profiles of human vowels and vowel-like baboon grunts: the role of vocalizer body size and voice-acoustic allometry

Key voice features--fundamental frequency (F0) and formant frequencies--can vary extensively between individuals. Much of the variation can be traced to differences in the size of the larynx and vocal-tract cavities, but whether these differences in turn simply reflect differences in speaker body size (i.e., neutral vocal allometry) remains unclear. Quantitative analyses were therefore undertaken to test the relationship between speaker body size and voice F0 and formant frequencies for human vowels. To test the taxonomic generality of the relationships, the same analyses were conducted on the vowel-like grunts of baboons, whose phylogenetic proximity to humans and similar vocal production biology and voice acoustic patterns recommend them for such comparative research. For adults of both species, males were larger than females and had lower mean voice F0 and formant frequencies. However, beyond this, F0 variation did not track body-size variation between the sexes in either species, nor within sexes in humans. In humans, formant variation correlated significantly with speaker height but only in males and not in females. Implications for general vocal allometry are discussed as are implications for speech origins theories, and challenges to them, related to laryngeal position and vocal tract length.     

A framework for the study of vocal registers

Register transitions are divided into two classes, periodicity transitions and timbre transitions. Periodicity transitions refer to changes in vocal quality that occur whenever glottal pulses are perceived as individual events rather than as a continuous auditory stimulus. Timbre transitions refer to changes in vocal quality associated with changes in spectral balance. Physiologically, these can be quantified with an abduction quotient. The singing registers appear to be based on timbre transitions resulting from subglottal resonances that interfere with the vocal fold driving pressure. Four of the major singing register shifts are predicted (in frequency and relative importance) on the basis of the first subglottal formant. Strategies for register equalization are proposed on the basis of supraglottal formant tuning (vowel modification) and adjustments in glottal adduction.     

Comparison of vocal tract formants in singing andnonperiodic phonation

The skilled use of nonperiodic phonation techniques in combination with spectrum analysis has been proposed here as a practical method for locating formant frequencies in the singing voice. The study addresses the question of the degree of similarity between sung phonations and their nonperiodic imitations, with respect to both frequency of the first two formants as well as posture of the vocal tract. Using magnetic resonance imaging (MRI), linear predictive coding (LPC), and spectrum analysis, two types of nonperiodic phonation (ingressive and vocal fry) are compared with singing phonations to determine the degree of similarity/difference in acoustic and spatial dimensions of the vocal tract when these phonation types are used to approximate the postures of singing. In comparing phonation types, the close similarity in acoustic data in combination with the relative dissimilarity in spatial data indicates that the accurate imitations are not primarily the result of imitating the singing postures, but have instead an aural basis.     

A comparison of vocal tract perturbation patterns based on statistical and acoustic considerations

The purpose of this study was to investigate the relation between vocal tract deformation patterns obtained from statistical analyses of a set of area functions representative of a vowel repertoire, and the acoustic properties of a neutral vocal tract shape. Acoustic sensitivity functions were calculated for a mean area function based on seven different speakers. Specific linear combinations of the sensitivity functions corresponding to the first two formant frequencies were shown to possess essentially the same amplitude variation along the vocal tract length as the statistically derived deformation patterns reported in previous studies.     

A Comparison of Two Methods of Formant Frequency Estimation for High-Pitched Voices

This study sought to compare formant frequencies estimated from natural phonation to those estimated using two methods of artificial laryngeal stimulation: (1) stimulation of the vocal tract using an artificial larynx placed on the neck and (2) stimulation of the vocal tract using an artificial larynx with an attached tube placed in the oral cavity. Twenty males between the ages of 18 and 45 performed the following three tasks on the vowels /a/ and /i/: (1) 4 seconds of sustained vowel, (2) 2 seconds of sustained vowel followed by 2 seconds of artificial phonation via a neck placement, and (3) 4 seconds of sustained vowel, the last two of which were accompanied by artificial phonation via an oral placement. Frequencies for formants 1-4 were measured for each task at second 1 and second 3 using linear predictive coding. These measures were compared across second 1 and second 3, as well as across all three tasks. Neither of the methods of artificial laryngeal stimulation tested in this study yielded formant frequency estimates that consistently agreed with those obtained from natural phonation for both vowels and all formants. However, when estimating mean formant frequency data for samples of large N, each of the methods agreed with mean estimations obtained from natural phonation for specific vowels and formants. The greatest agreement was found for a neck placement of the artificial larynx on the vowel /a/.     

“Hot Potato Voice” in Peritonsillitis: A Misnomer

The "hot potato voice" is widely recognized as a symptom of peritonsillar cellulitis or abscess; yet there have been no studies assessing the resonance characteristics of the vocal tract in peritonsillitis. Analysis was undertaken of formant frequencies in the articulation of the vowels /i:/. /a:/ and /u:/ in six subjects with peritonsillitis and compared with articulation once the peritonsillitis had settled. Significant variation was found in F1 when articulating /i:/ and in F2 when articulating /a:/, which are explainable by dyskinesis of the peritonsillar musculature. These findings were compared with six subjects articulating the same vowels with and without a hot potato in their mouth. Variation was found in both F1 and F2 when articulating /i:/, which can be related to interference of the potato with movement of the anterior tongue. The changes in the vocal tract differ in these two cases and the title "hot potato voice" in peritonsillitis is a misnomer.     

Some physical characteristics of the male falsetto voice

Previous research indicated that, as groups, male (bass/baritone) and female (soprano) professional singers tend to exhibit differing vocal tract and voice source behaviours. The use of an objective measure of voice [xeroradiographic-electrolaryngographic analysis (XEL)] revealed differences between the two voice types, especially at the highest sample pitches (e, 330 Hz for bass/baritones, and e″, 1,320 Hz for sopranos). XEL analysis combines two known techniques, i.e., soft-tissue radiographic imaging (xeroradiography), and an analysis of voice-source vibratory patterning (electrolaryngography). Subsequent to this investigation, interest centered on the male professional falsetto voice over a two-octave range (E 165 Hz to e′ 660 Hz) using a sample (n=9) of professional countertenors. Results suggest that there are characteristic trends in the patterning of the male professional falsetto register, but there is also evidence of within-group variability. The subjects significantly increased the size of the pharyngeal tube area during phonation. ANOVA and Trend Analysis revealed ventricular space as the only measure to expand systematically and consistently as sung pitch increases.