Vocal-fold collision mass as a differentiator between registers in the low-pitch range

Hemi-laryngeal Setup for Studying Vocal Fold Vibration in Three Dimensions

The voice of humans and most non-human mammals is generated in the larynx through self-sustaining oscillation of the vocal folds. Direct visual documentation of vocal fold vibration is challenging, particularly in non-human mammals. As an alternative, excised larynx experiments provide the opportunity to investigate vocal fold vibration under controlled physiological and physical conditions. However, the use of a full larynx merely provides a top view of the vocal folds, excluding crucial portions of the oscillating structures from observation during their interaction with aerodynamic forces. This limitation can be overcome by utilizing a hemi-larynx setup where one half of the larynx is mid-sagittally removed, providing both a superior and a lateral view of the remaining vocal fold during self-sustained oscillation. Here, a step-by-step guide for the anatomical preparation of hemi-laryngeal structures and their mounting on the laboratory bench is given. Exemplary phonation of the hemi-larynx preparation is documented with high-speed video data captured by two synchronized cameras (superior and lateral views), showing three-dimensional vocal fold motion and corresponding time-varying contact area. The documentation of the hemi-larynx setup in this publication will facilitate application and reliable repeatability in experimental research, providing voice scientists with the potential to better understand the biomechanics of voice production.

Three-dimensional posture changes of the vocal fold from paired intrinsic laryngeal muscles

OBJECTIVES/HYPOTHESIS

Although the geometry of the vocal fold medial surface affects voice quality and is critical in the treatment of glottic insufficiency, the prephonatory shape of the vocal fold medial surface is not well understood. In this study, we activated intrinsic laryngeal muscles individually and in combinations, and recorded the temporal sequence and precise three-dimensional configurational changes of the vocal fold medial surface.

STUDY DESIGN

In vivo canine hemilarynx model.

METHODS

A hemilaryngectomy was performed in an in vivo canine model and ink was used to mark the medial surface of the in situ vocal fold in a grid-like fashion. The thyroarytenoid (TA), lateral cricoarytenoid (LCA), cricothyroid (CT), and posterior cricoarytenoid (PCA) muscles were stimulated individually and in combinations. A right-angle prism whose hypotenuse formed the glottal midline provided two distinct views of the medial surface for a high-speed digital camera. Image-processing package DaVis (LaVision Inc., Goettingen, Germany) allowed time series cross-correlation analysis for three-dimensional deformation calculations of the vocal fold medial surface.

RESULTS

Combined TA and LCA activation yields an evenly adducted rectangular glottal surface. Addition of thyroarytenoid to cricoarytenoid adducts the vocal fold from inferior to superior in a graded fashion allowing formation of a divergent glottis. Posterior cricoarytenoid has a bimodal relationship with thyroarytenoid favoring abduction. Cricothyroid and lateral cricoarytenoid yield unique glottal postures necessary but likely not conducive for efficient phonation.

CONCLUSIONS

Understanding the three-dimensional geometry of the vocal fold medial surface will help us better understand the cause-effect relationship between laryngeal physiology and phonation.

LEVEL OF EVIDENCE

NA Laryngoscope, 127:656-664, 2017.

Bi-stable vocal fold adduction: a mechanism of modal-falsetto register shifts and mixed registration

The origin of vocal registers has generally been attributed to differential activation of cricothyroid and thyroarytenoid muscles in the larynx. Register shifts, however, have also been shown to be affected by glottal pressures exerted on vocal fold surfaces, which can change with loudness, pitch, and vowel. Here it is shown computationally and with empirical data that intraglottal pressures can change abruptly when glottal adductory geometry is changed relatively smoothly from convergent to divergent. An intermediate shape between large convergence and large divergence, namely, a nearly rectangular glottal shape with almost parallel vocal fold surfaces, is associated with mixed registration. It can be less stable than either of the highly angular shapes unless transglottal pressure is reduced and upper stiffness of vocal fold tissues is balanced with lower stiffness. This intermediate state of adduction is desirable because it leads to a low phonation threshold pressure with moderate vocal fold collision. Achieving mixed registration consistently across wide ranges of F0, lung pressure, and vocal tract shapes appears to be a balancing act of coordinating laryngeal muscle activation with vocal tract pressures. Surprisingly, a large transglottal pressure is not facilitative in this process, exacerbating the bi-stable condition and the associated register contrast.

Laryngeal muscle activity and vocal fold adduction during chest, chestmix, headmix, and head registers in females

HYPOTHESIS

Commercial singers produce chestmix register by maintaining or increasing adduction of the vocal processes (VPs) and by engaging the thyroarytenoid (TA) muscle to a greater degree than they would to produce head register.

STUDY DESIGN

Prospective cohort study.

METHODS

Simultaneous recordings of TA and cricothyroid (CT) muscle activity, videonasendoscopy, and audio were obtained from seven female singers during production of a variety of midrange pitches in chest, chestmix, headmix, and head registers. Fast Fourier transforms were performed to measure the energy in the fundamental frequency and in mid and upper frequency harmonics to determine if the productions that were judged as perceptually distinct registers also showed distinctive acoustic characteristics. Then, measures of TA and CT muscle activity and vocal fold adduction ratings were obtained to determine how these varied as a function of pitch and register.

RESULTS

Spectral tilt increased as subjects shifted from chest to chestmix to headmix and finally into head register. For same pitch phonation, subjects increased TA muscle activity and vocal fold adduction as they shifted register from head to headmix to chestmix to chest, particularly during production of higher frequencies. CT activity appeared to be more related to pitch rather than register control.

CONCLUSION

Nonclassically trained singers were able to produce pitches at the high end of the midrange in chestmix register by increasing TA muscle activity and adduction of the VPs.

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.

Biomechanical modeling of register transitions and the role of vocal tract resonators

Biomechanical modeling and bifurcation theory are applied to study phonation onset and register transition. A four-mass body-cover model with a smooth geometry is introduced to reproduce characteristic features of chest and falsetto registers. Sub- and supraglottal resonances are modeled using a wave-reflection model. Simulations for increasing and decreasing subglottal pressure reveal that the phonation onset exhibits amplitude jumps and hysteresis referring to a subcritical Hopf bifurcation. The onset pressure is reduced due to vocal tract resonances. Hysteresis is observed also for the voice breaks at the chest-falsetto transition. Varying the length of the subglottal resonator has only minor effects on this register transition. Contrarily, supraglottal resonances have a strong effect on the pitch, at which the chest-falsetto transition is found. Experiment of glissando singing shows that the supraglottis has indeed an influence on the register transition.

Subglottal pressure and normalized amplitude quotient variation in classically trained baritone singers

The subglottal pressure (Ps) and voice source characteristics of five professional baritone singers have been analyzed and the normalized amplitude quotient (NAQ), defined as the ratio between peak-to-peak pulse amplitude and the negative peak of the differentiated flow glottogram and normalized with respect to the period time, was used as an estimate of glottal adduction. The relationship between Ps and NAQ has been investigated in female subjects in two earlier studies. One of these revealed NAQ differences between both singing styles and phonation modes, and the other, based on register differences in female musical theatre singers, showed that NAQ differed between registers for the same Ps value. These studies thus suggest that NAQ and its variation with Ps represent a useful parameter in the analysis of voice source characteristics. The present study aims at increasing our knowledge of the NAQ parameter further by finding out how it varies with pitch and Ps in professional classically trained baritone singers, singing at high and low pitch (278 Hz and 139 Hz, respectively). Ten equally spaced Ps values were selected from three takes of the syllable [pae:], initiated at maximum vocal loudness and repeated with a continuously decreasing vocal loudness. The vowel sounds following the selected Ps peaks were inverse filtered. Data on peak-to-peak pulse amplitude, maximum flow declination rate and NAQ are presented.

What do male singers mean by modal and falsetto register? An investigation of the glottal voice source

The voice source differs between modal and falsetto registers, but singers often try to reduce the associated timbral differences, some even doubting that there are any. A total of 54 vowel sounds sung in falsetto and modal register by 13 male more or less experienced choir singers were analyzed by inverse filtering and electroglottography. Closed quotient, maximum flow declination rate, peak-to-peak airflow amplitude, normalized amplitude quotient, and level difference between the two lowest source spectrum partials were determined, and systematic differences were found in all singers, regardless of experience of singing. The observations seem compatible with previous observations of thicker vocal folds in modal register.

Aerodynamic and acoustic effects of abrupt frequency changes in excised larynges

PURPOSE

To determine the aerodynamic and acoustic effects due to a sudden change from chest to falsetto register or vice versa. It was hypothesized that the continuous change in subglottal pressure and flow rate alone (pressure-flow sweep [PFS]) can trigger a mode change in the canine larynx.

METHOD

Ten canine larynges were each mounted over a tapered tube that supplied pressurized, heated, and humidified air. Glottographic signals were recorded during each PFS experiment, during which airflow was increased in a gradual manner for a period of 20-30 s.

RESULTS

Abrupt changes in fundamental frequency (F(0)) and mode of vibration occurred during the PFS in the passive larynx without any change in adduction or elongation. The lower frequency mode of oscillation of the vocal folds, perceptually identified as the chest register, had relatively large amplitude oscillation, significant vocal fold contact, a rich spectral content, and a relatively loud audio signal. The higher frequency mode of oscillation, perceptually identified as falsetto, had little or no vocal fold contact and a dominant first partial. Relatively abrupt F(0) changes also occurred for gradual adduction changes, with the chest register corresponding to greater adduction, falsetto to less adduction.

Acoustic and perceptual analysis of modal and falsetto registers in females with dysphonia

Modal and falsetto registers are the basic vocal qualities used in female speaking voices. The purpose of this study was to identify the frequency at which modal register changed to falsetto register and the frequency range of each modal and falsetto register produced under three loudness levels: soft, comfortable and loud phonations in normal and dysphonic speakers. These data provide information on the relationship between vocal registers. It is hypothesized that vocal pathologies affect the frequency at which register change from one mode to another mode. Fifteen dysphonic and 15 non-dysphonic females were assessed on their ability to produce tone series from the lowest to the highest frequency at soft, comfortable and loud phonations. Fourteen listeners served as judges to identify the first production of falsetto voice in each tone series. The first falsetto tone perceived was considered to represent the frequency at which the modal-falsetto register change occurred perceptually. The change from modal to falsetto register in the tone series occurred between G4 (360.74 Hz) and B4 (485.23 Hz) in the dysphonic group and between A4 (421.00 Hz) and B4 (476.13 Hz) in the non-dysphonic group among the three loudness levels. The results showed that the presence of dysphonia affected the production of vocal registers The dysphonic group demonstrated the modal-falsetto register change at a significantly lower frequency and reduced frequency range in the modal register than those of the non-dysphonic group in the soft and comfortable phonations. In producing falsetto register, the dysphonic group demonstrated reduced ability in producing falsetto register in soft and loud phonations when compared to the non-dysphonic group. Physiological explanations are used to account for the observations.

Pitch-synchronous changes in the anterior cricothyroid space during singing

Pitch-synchronous changes in the anterior cricothyroid (CT) space were registered with ultrasonography (USG) for ten healthy subjects (5 males, 5 females) during the production of musical fifths throughout the whole voice range. One of the males and one of the females were trained amateur singers, the other subjects were choir singers. The average decrease in CT space per a musical fifth was 1.3-2.4 mm for the males and 1.0-1.8 mm for the females; the average decrease was smaller in the middle of the pitch range for both genders. The results suggest that (1) USG can be used for detection of pitch-synchronous changes in the CT space; (2) these changes are dependent on pitch range; and (3) more trained singers tend to have somewhat smaller changes than less trained subjects at certain frequencies. The results seem to indicate that F0 control mechanism varies according to pitch range and register, and possibly according to individual structure and vocal technique related differences.

An Investigation of a Modal-Falsetto Register Transition Hypothesis Using Helox Gas

This study concerned the effect of the first subglottal formant (F1') on the modal-falsetto register transition in males and females. Phonations using air and a helium-oxygen mixture (helox) were used in a comparative study to tease apart possible acoustic and myoelastic contributions to involuntary register transitions. Recordings of the first subglottal formant and its accompanying bandwidths, and the lower and upper shift point marking the outer boundaries of abrupt register transitions, were obtained via a neck-mounted accelerometer, and analyzed using spectrograms and power spectra on a K-5500 Sona-Graph. The four subjects had their hearing masked bilaterally with speech level noise to increase the likelihood of involuntary register transition via minimized auditory feedback. In three of the four test subjects registration was surmised to be primarily a laryngeal event, as evidenced by the similar frequency dependency of voice breaks in both air and helox. It may be hypothesized that subglottal resonance influenced register transition in the fourth subject, as voice breaks rose with helox-induced phonation; however, this result did not reach statistical significance. Therefore, in this experiment subglottal resonance was not found to have a significant influence on register transition as originally hypothesized.

A report on alterations to the speaking and singing voices of four women following hormonal therapy with virilizing agents

Four women aged between 27 and 58 years sought otolaryngological examination due to significant alterations to their voices, the primary concerns being hoarseness in vocal quality, lowering of habitual pitch, difficulty projecting their speaking voices, and loss of control over their singing voices. Otolaryngological examination with a mirror or flexible laryngoscope revealed no apparent abnormality of vocal fold structure or function, and the women were referred for speech pathology with diagnoses of functional dysphonia. Objective acoustic measures using the Kay Visipitch indicated significant lowering of the mean fundamental frequency for each woman, and perceptual analysis of the patients' voices during quiet speaking, projected voice use, and comprehensive singing activities revealed a constellation of features typically noted in the pubescent male. The original diagnoses of a functional dysphonia were queried, prompting further exploration of each woman's medical history, revealing in each case onset of vocal symptoms shortly after commencing treatment for conditions with medications containing virilizing agents (eg, Danocrine (danazol), Deca-Durabolin (nandrolene decanoate), and testosterone). Although some of the vocal symptoms decreased in severity with the influences from 6 months voice therapy and after withdrawal from the drugs, a number of symptoms remained permanent, suggesting each subject had suffered significant alterations in vocal physiology, including muscle tissue changes, muscle coordination dysfunction, and propioceptive dysfunction. This retrospective study is presented in order to illustrate that it was both the projected speaking voice and the singing voice that proved so highly sensitive to the virilization effects. The implications for future prospective research studies and responsible clinical practice are discussed.

On pitch jumps between chest and falsetto registers in voice: data from living and excised human larynges

The paper offers a new concept of studying abrupt chest-falsetto register transitions (jumps) based on the theory of nonlinear dynamics. The jumps were studied in an excised human larynx and in three living subjects (one female and two male). Data from the excised larynx revealed that a small and gradual change in tension of the vocal folds can cause an abrupt change of register and pitch. This gives evidence that the register jumps are manifestations of bifurcations in the vocal-fold vibratory mechanism. A hysteresis was observed; the upward register jump occurred at higher pitches and tensions than the downward jump. Due to the hysteresis, the chest and falsetto registers can be produced with practically identical laryngeal adjustments within a certain range of longitudinal tensions. The magnitude of the frequency jump was measured as the "leap ratio" F0F:F0C (fundamental frequency of the falsetto related to that of the chest register) and alternatively expressed as a corresponding musical interval, termed the "leap interval." Ranges of this leap interval were found to be different for the three living subjects (0-5 semitones for the female, 5-10 and 10-17 for the two males, respectively). These differences are considered to reflect different biomechanical properties of the vocal folds of the examined subjects. A small magnitude of the leap interval was associated with a smooth chest-falsetto transition in the female subject.

Simultaneous videofluorographic and dual-channel electroglottographic registration of the vertical laryngeal position in various phonatory tasks

Simultaneous tracking of the vertical laryngeal position in various phonatory tasks was performed for 2 subjects (one male, one female) using dual-channel electroglottography (EGG) and videofluorography (videofluoroscopy). The tasks included phonation on [a:] with voluntary repeated (1) heightening and (2) lowering of the laryngeal position; alternation between [a:] and phonation on (3) [b], (4) [m], and (5) the voiced bilabial fricative [beta:]; and (6) production of the corner vowels [a, i, u]. EGG and videofluorography agreed about the direction of changes in the vertical laryngeal position in most cases. Most disagreements were found in the amount of changes. Reasons for the discrepancies, including, for example, changes in the resting position of the larynx and anteroposterior movements of the cartilages, are discussed. It can be concluded that dual-channel EGG is a valuable clinical and pedagogical tool for the analysis of the vertical displacement of larynx in well-specified phonatory tasks. The method should act most reliably on separately phonated vowels. Its applicability for studying laryngeal biomechanics more wholistically, however, is limited.

Meaningful features of voice range profiles from patients with organic vocal fold pathology: a preliminary study

This preliminary study identifies features that have the potential to be meaningful descriptors of voice range profiles (VRPs) for 15 patients with organic vocal fold pathologies before and after laryngeal surgery. This study also explores the utility of the VRP as an outcome measure of change in vocal function after surgery. Potentially meaningful features for these patients are the semitone range, intensity level of the lower contour, frequency locus of the lower frequency values, smoothness of the contours, and the presence of intermittencies in the VRP contours. These features are not suggested for differential diagnosis, but for aiding the understanding of each individual patient's phonatory status. Initial use of these features suggests that the VRP may be a useful outcome measure for these patients.

A physiological and acoustic study on voiced bilabial fricative/beta:/as a vocal exercise

The voiced bilabial fricative/beta:/has been used as a vocal exercise. The present study investigated the effects of the exercise on voice production and voice source. This study compared vowel phonation on the syllable /a:p/ with the production of the exercise and vowel phonation before and immediately after the exercise. The methods were (a) dual-channel electroglottography, from which the vertical laryngeal position was derived, (b) electromyography using surface electrodes, and (c) inverse filtering of the acoustic signal to obtain an estimate of the voice source. In the production of /beta:/ as compared with vowel phonation in most of the cases, the vertical laryngeal position seemed to be higher, the muscular activity of the larynx lower, and the slope of the voice source spectrum steeper. In vowel phonation after the exercise, the muscular activity seemed to be lower in most cases, although the voice source remained unchanged. This seems to indicate improved vocal economy.