Electroglottographic wavegrams: a technique for visualizing vocal fold dynamics noninvasively

A method for analyzing and displaying electroglottographic (EGG) signals (and their first derivative, DEGG) is introduced: the electroglottographic wavegram ("wavegram" hereafter). To construct a wavegram, the time-varying fundamental frequency is measured and consecutive individual glottal cycles are identified. Each cycle is locally normalized in duration and amplitude, the signal values are encoded by color intensity and the cycles are concatenated to display the entire voice sample in a single image, similar as in sound spectrography. The wavegram provides an intuitive means for quickly assessing vocal fold contact phenomena and their variation over time. Variations in vocal fold contact appear here as a sequence of events rather than single phenomena, taking place over a certain period of time, and changing with pitch, loudness and register. Multiple DEGG peaks are revealed in wavegrams to behave systematically, indicating subtle changes of vocal fold oscillatory regime. As such, EGG wavegrams promise to reveal more information on vocal fold contacting and de-contacting events than previous methods.     

Vocal tract area functions and formant frequencies in opera tenors' modal and falsetto registers

According to recent model investigations, vocal tract resonance is relevant to vocal registers. However, no experimental corroboration of this claim has been published so far. In the present investigation, ten professional tenors' vocal tract configurations were analyzed using MRI volumetry. All subjects produced a sustained tone on the pitch F4 (349 Hz) on the vowel /a/ (1) in modal and (2) in falsetto register. The area functions were estimated from the MRI data and their associated formant frequencies were calculated. In a second condition the same subjects repeated the same tasks in a sound treated room and their formant frequencies were estimated by means of inverse filtering. In both recordings similar formant frequencies were observed. Vocal tract shapes differed between modal and falsetto register. In modal as compared to falsetto the lip opening and the oral cavity were wider and the first formant frequency was higher. In this sense the presented results are in agreement with the claim that the formant frequencies differ between registers.     

Laryngeal and pharyngeal behavior in countertenor and baritone singing—A videofiberscopic study

Changes in vocal tract configuration during singing were studied in four semiprofessional countertenors and one professional bass-baritone, by means of fiberoptic laryngoscopy. All of the countertenors showed a marked narrowing of the lower pharynx with increasing pitch when they used their countertenor voice (CT voice) but only a slight narrowing when using their baritone voice (B voice). The bass-baritone's pharynx remained unchanged with increasing pitch. Increasing loudness gave a widening of the pharynx in three of the four countertenors' CT voices, whereas no change was observed for the countertenors' B voices or for the bass-baritone voice. Vocal fold length seemed to decrease in one countertenor's B voice and in the bass-baritone with increasing loudness. Thus, the countertenors in this study exhibit several characteristic patterns of vocal tract gestures in countertenor voice that differ from both their own baritone voices and from the bass-baritone.     

Three registers in an untrained female singer analyzed by videokymography, strobolaryngoscopy and sound spectrography

There has been a lack of objective data on the singing voice registers, particularly on the so called "whistle" register, occurring in the top part of the female pitch range, which is accessible only to some singers. This study offers unique strobolaryngoscopic and high-speed (7812.5 imagess) videokymographic data on the vocal fold behavior of an untrained female singer capable of producing three distinct voice qualities, i.e., the chest, head and whistle registers. The sound was documented spectrographically. The transition from chest to head register, accompanied by pitch jumps, occurred around tones B4-C#5 (500-550 Hz) and was found to be associated with a slight decrease in arytenoids adduction, resulting in decrease of the closed quotient. The register shifts from head to whistle, also accompanied by pitch jumps, occurred around tones E5-B5 (670-1000 Hz) without any noticeable changes in arytenoids adduction. Some evidence was found for the vocal tract influence on this transition. The mechanism of the vocal fold vibration in whistle register was found principally similar to that at lower registers: vibrations along the whole glottal length and vertical phase differences (indicated by sharp lateral peaks in videokymography) were seen on the vocal folds up to the highest tone G6 (1590 Hz).     

Performance characterization of human pitch control system: an acoustic approach

The performance of the human pitch control system was characterized by measurement of the speed of pitch shift and pitch shift response speed (inverse of reaction time) at various initial pitch and loudness levels. Data from three nonsinger adult male subjects and one professional singer suggest a strong inverse correlation (r greater than 0.78) between initial pitch and rate of pitch rise. This study showed no significant relation between initial loudness and rate of pitch rise. Also, vocal response speed showed no significant relation with either initial pitch or loudness. However, it is suggested that pitch shift response speed might be related to the second formant frequency of the target vowel. A composite index of pitch control performance capacity was defined as the product of response speed and vocal fold contractile velocity. From experimental data, the composite index was able to reflect a distinct 74% superior performance by the professional singer (relative to the average maximum performance capacity of nonsingers). It is suggested that the product-based composite index of performance capacity can serve as a sensitive means for vocal proficiency determination.     

The abduction quotient related to vocal quality

The abduction quotient, a measure of effective glottal width, was obtained for electroglottographic recordings from a professional operatic baritone singer. The subject produced repeated tokens of the voice qualities breathy, normal, and pressed (or constricted) in both a speech and a singing manner. In the singing manner, the subject produced the three vocal qualities at three pitch levels and three loudness levels. The abduction quotient decreased from breathy to pressed voice, suggesting that the measure corresponds to effective glottal width. The measure was found to be consistently low during all conditions of singing, suggesting that the subject produced all singing tokens with relatively strong laryngeal adduction at the vocal process level. Although the results of this study support the validity and usefulness of the abduction quotient, further verification is needed.     

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.     

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.     

Vocal tract length perturbation and its application to male-female vocal tract shape conversion

An alternative and complete derivation of the vocal tract length sensitivity function, which is an equation for finding a change in formant frequency due to perturbation of the vocal tract length [Fant, Quarterly Progress and Status Rep. No. 4, Speech Transmission Laboratory, Kungliga Teknisha Hogskolan, Stockholm, 1975, pp. 1-14] is presented. It is based on the adiabatic invariance of the vocal tract as an acoustic resonator and on the radiation pressure on the wall and at the exit of the vocal tract. An algorithm for tuning the vocal tract shape to match the formant frequencies to target values, such as those of a recorded speech signal, which was proposed in Story [J. Acoust. Soc. Am. 119, 715-718 (2006)], is extended so that the vocal tract length can also be changed. Numerical simulation of this extended algorithm shows that it can successfully convert between the vocal tract shapes of a male and a female for each of five Japanese vowels.     

Effects on the glottal voice source of vocal loudness variation in untrained female and male voices

Subglottal pressure is one of the main voice control factors, controlling vocal loudness. In this investigation the effects of subglottal pressure variation on the voice source in untrained female and male voices phonating at a low, a middle, and a high fundamental frequency are analyzed. The subjects produced a series of /pae/ syllables at varied degrees of vocal loudness, attempting to keep pitch constant. Subglottal pressure was estimated from the oral pressure during the /p/ occlusion. Ten subglottal pressure values, approximately equidistantly spaced within the pressure range used, were identified, and the voice source of the vowels following these pressure values was analyzed by inverse filtering the airflow signal as captured by a Rothenberg mask. The maximum flow declination rate (MFDR) was found to increase linearly with subglottal pressure, but a given subglottal pressure produced lower values for female than for male voices. The closed quotient increased quickly with subglottal pressure at low pressures and slowly at high pressures, such that the relationship can be approximated by a power function. For a given subglottal pressure value, female voices reached lower values of closed quotient than male voices.     

Relationship between changes in voice pitch and loudness

Changes in mean fundamental frequency accompanying changes in loudness of phonation are analyzed in 9 professional singers, 9 nonsingers, and 10 male and 10 female patients suffering from vocal functional dysfunction. The subjects read discursive texts with noise in earphones, and some also at voluntarily varied vocal loudness. The healthy subjects phonated as softly and as loudly as possible at various fundamental frequencies throughout their pitch ranges, and the resulting mean phonetograms are compared. Mean pitch was found to increase by about half-semitones per decibel sound level. Grossly, the subject groups gave similar results, although the singers changed voice pitch more than the nonsingers. The voice pitch changes may be explained as passive results of changes of subglottal pressure required for the sound level variation.     

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.     

Measurement of temporal changes in vocal tract area function from 3D cine-MRI data

A 3D cine-MRI technique was developed based on a synchronized sampling method [Masaki et al., J. Acoust. Soc. Jpn. E 20, 375-379 (1999)] to measure the temporal changes in the vocal tract area function during a short utterance /aiueo/ in Japanese. A time series of head-neck volumes was obtained after 640 repetitions of the utterance produced by a male speaker, from which area functions were extracted frame-by-frame. A region-based analysis showed that the volumes of the front and back cavities tend to change reciprocally and that the areas near the larynx and posterior edge of the hard palate were almost constant throughout the utterance. The lower four formants were calculated from all the area functions and compared with those of natural speech sounds. The mean absolute percent error between calculated and measured formants among all the frames was 4.5%. The comparison of vocal tract shapes for the five vowels with those from the static MRI method suggested a problem of MRI observation of the vocal tract: data from static MRI tend to result in a deviation from natural vocal tract geometry because of the gravity effect.     

A methodological and preliminary study on the acoustic effect of a trumpet player's vocal tract

A methodological study is presented to examine the acoustic role of the vocal tract in playing the trumpet. Preliminary results obtained for one professional player are also shown to demonstrate the effectiveness of the method. Images of the vocal tract with a resolution of 0.5 mm (2 mm in thickness) were recorded with magnetic resonance imaging to observe the tongue posture and estimate the vocal-tract area function during actual performance. The input impedance was then calculated for the player's air column including both the supra- and subglottal tracts using an acoustic tube model including the effect of wall losses. Finally, a time-domain blowing simulation by Adachi and Sato [J. Acoust. Soc. Am. 99, 1200-1209 (1996)] was performed with a model of the lips. In this simulation, the oscillating frequency of the lips was slightly affected by using different shapes of the vocal tract measured for the player. In particular, when the natural frequency of the lips was gradually increased, the transition to the higher mode occurred at different frequencies for different vocal-tract shapes. Furthermore, simulation results showed that the minimum blowing pressure required to attain the lip oscillation can be reduced by adjusting the vocal-tract shape properly.     

The relationship of vocal tract shape to three voice qualities

Three-dimensional vocal tract shapes and consequent area functions representing the vowels [i, ae, a, u] have been obtained from one male and one female speaker using magnetic resonance imaging (MRI). The two speakers were trained vocal performers and both were adept at manipulation of vocal tract shape to alter voice quality. Each vowel was performed three times, each with one of the three voice qualities: normal, yawny, and twangy. The purpose of the study was to determine some ways in which the vocal tract shape can be manipulated to alter voice quality while retaining a desired phonetic quality. To summarize any overall tract shaping tendencies mean area functions were subsequently computed across the four vowels produced within each specific voice quality. Relative to normal speech, both the vowel area functions and mean area functions showed, in general, that the oral cavity is widened and tract length increased for the yawny productions. The twangy vowels were characterized by shortened tract length, widened lip opening, and a slightly constricted oral cavity. The resulting acoustic characteristics of these articulatory alterations consisted of the first two formants (F1 and F2) being close together for all yawny vowels and far apart for all the twangy vowels.     

Cyclicity of laryngeal cavity resonance due to vocal fold vibration

Acoustic effects of the time-varying glottal area due to vocal fold vibration on the laryngeal cavity resonance were investigated based on vocal tract area functions and acoustic analysis. The laryngeal cavity consists of the vestibular and ventricular parts of the larynx, and gives rise to a regional acoustic resonance within the vocal tract, with this resonance imparting an extra formant to the vocal tract resonance pattern. Vocal tract transfer functions of the five Japanese vowels uttered by three male subjects were calculated under open- and closed-glottis conditions. The results revealed that the resonance appears at the frequency region from 3.0 to 3.7 kHz when the glottis is closed and disappears when it is open. Real spectra estimated from open- and closed-glottis periods of vowel sounds also showed the on-off pattern of the resonance within a pitch period. Furthermore, a time-domain acoustic analysis of vowels indicated that the resonance component could be observed as a pitch-synchronized rise-and-fall pattern of the bandpass amplitude. The cyclic nature of the resonance can be explained as the laryngeal cavity acting as a closed tube that generates the resonance during a closed-glottis period, but damps the resonance off during an open-glottis period.     

Performance demands and the performer's vocal capabilities

Performers could benefit by knowing in advance and by objective means, what vocal requirements for a particular role or performance are potentially harmful to them. By combining the concept of the “phonetogram” (F₀ — SPL Profile) with automatic pitch extraction of vocal performances, a contour of the vocal performance demands can be superimposed on the profile of the individual's vocal capabilities. Vocal productions that are near to or exceeding the vocal capabilities of a performer can be presumed to be potentially hazardous. Likewise, performance demands that are clearly within the profile of a given individual can be presumed to be nonhazardous with respect to pitch and amplitude range.     

The effect of head position on glottic closure in patients with unilateral vocal fold paralysis

The present study was designed to assess the effect of head position on glottic closure as reflected in airflow rates (open quotient and maximum flow declination rate), in patients with unilateral vocal fold paralysis. Ten patients, 2 males and 8 females ranging in age from 40 to 75, with a mean age of 57.3, served as subjects. Airflow measures were taken during sustained phonation of two vowels (/i/ and /a/) in 3 head positions (center, right, left). Vowels /i/ and /a/ were produced at subject's comfortable pitch and loudness, with random ordering of both vowel order and head orientation. Subjects were trained to focus eye gaze on right and left markers (70-degree angle) and a central marker at eye level directly in front of the subject. Theoretically, if turning the head during phonation alters the laryngeal anatomic relationship by bringing the vocal folds in closer proximity to one another, then airflow rate should lessen. Our results indicate that head position does not improve glottic closure in these patients, which is in contrast to previously published research.(1) Our results question the utility and underlying theoretical construct for the use of head turning as a therapeutic technique for improvement of voice in patients with unilateral vocal fold paralysis.     

Dependence of phonation threshold pressure on vocal tract acoustics and vocal fold tissue mechanics

Analytical and computer simulation studies have shown that the acoustic impedance of the vocal tract as well as the viscoelastic properties of vocal fold tissues are critical for determining the dynamics and the energy transfer mechanism of vocal fold oscillation. In the present study, a linear, small-amplitude oscillation theory was revised by taking into account the propagation of a mucosal wave and the inertive reactance (inertance) of the supraglottal vocal tract as the major energy transfer mechanisms for flow-induced self-oscillation of the vocal fold. Specifically, analytical results predicted that phonation threshold pressure (Pth) increases with the viscous shear properties of the vocal fold, but decreases with vocal tract inertance. This theory was empirically tested using a physical model of the larynx, where biological materials (fat, hyaluronic acid, and fibronectin) were implanted into the vocal fold cover to investigate the effect of vocal fold tissue viscoelasticity on Pth. A uniform-tube supraglottal vocal tract was also introduced to examine the effect of vocal tract inertance on Pth. Results showed that Pth decreased with the inertive impedance of the vocal tract and increased with the viscous shear modulus (G") or dynamic viscosity (eta') of the vocal fold cover, consistent with theoretical predictions. These findings supported the potential biomechanical benefits of hyaluronic acid as a surgical bioimplant for repairing voice disorders involving the superficial layer of the lamina propria, such as scarring, sulcus vocalis, atrophy, and Reinke's edema.     

Acoustic roles of the laryngeal cavity in vocal tract resonance

The acoustic effects of the laryngeal cavity on the vocal tract resonance were investigated by using vocal tract area functions for the five Japanese vowels obtained from an adult male speaker. Transfer functions were examined with the laryngeal cavity eliminated from the whole vocal tract, volume velocity distribution patterns were calculated, and susceptance matching analysis was performed between the laryngeal cavity and the vocal tract excluding the laryngeal cavity (vocal tract proper). It was revealed that the laryngeal cavity generates one of the formants of the vocal tract, which is the fourth in the present study. At this formant, the resonance of the laryngeal cavity (the 1/4 wavelength resonance) induces the open-tube resonance of the vocal tract proper (the 3/2 wavelength resonance). At the other formants, on the other hand, the vocal tract proper acts as a closed tube, because the laryngeal cavity has only a small contribution to generating these formants and the effective closed end of the whole vocal tract is the junction between the laryngeal cavity and the vocal tract proper.