On the use of the derivative of electroglottographic signals for characterization of nonpathological phonation

The Physiology of Vocal Damping: Historical Overview and Descriptive Insights in Professional Singers

OBJECTIVE

Vocal damping has been historically described as a distinctive phonatory glottic behavior where the posterior part of the vocal folds is strongly adducted and vibration occurs in the anterior part. The aim of the present descriptive study is to analyze anterior glottis phonation patterns in professional singers through a multidimensional approach, in order to better understand the physiological underpinnings of vocal damping and their relation to glottic vibratory mechanisms.

METHODS

Ten professional singers (five males and five females) with no vocal complaints were recruited. Each subject was asked to produce ascending and descending glissandos in a spontaneous way; sustained vowels and little sung fragments in vocal fry, chest voice, falsetto, and whistle register. Each singer was asked to produce - where possible - damping sounds. A multidimensional investigation including acoustic analysis, electroglottography, and videolaryngostroboscopy was carried out.

RESULTS

Among the enrolled singers, nine out of 10 successfully produced vocalizations with a typical anterior-vibrating glottic pattern indicative of damping. All nine singers achieved a damping glottic configuration when vocalizing in the falsetto register and five were consciously able to switch between a full-glottic falsetto and a damping falsetto upon request. Three male and two female singers were able to produce a damping glottic configuration while emitting whistle notes. Three male singers demonstrated damping glottic configurations when producing high pitched chest notes.

CONCLUSIONS

In conclusion, it is possible to state that damping is an existing and documentable glottic behavior, with a wide range of manifestations across vocal registers. The present preliminary study describes damping in the domains of chest voice, falsetto, and whistle register. A proper damping phenomenon, defined as the modification of the glottic vibratory boundaries according to pitch variations, is described for M2 emissions, both in male and female larynx. The analysis of passaggio patterns allows to describe damping-M2 as a possible vibratory submechanism.

Pragmatic De-Noising of Electroglottographic Signals

In voice analysis, the electroglottographic (EGG) signal has long been recognized as a useful complement to the acoustic signal, but only when the vocal folds are actually contacting, such that this signal has an appreciable amplitude. However, phonation can also occur without the vocal folds contacting, as in breathy voice, in which case the EGG amplitude is low, but not zero. It is of great interest to identify the transition from non-contacting to contacting, because this will substantially change the nature of the vocal fold oscillations; however, that transition is not in itself audible. The magnitude of the cycle-normalized peak derivative of the EGG signal is a convenient indicator of vocal fold contacting, but no current EGG hardware has a sufficient signal-to-noise ratio of the derivative. We show how the textbook techniques of spectral thresholding and static notch filtering are straightforward to implement, can run in real time, and can mitigate several noise problems in EGG hardware. This can be useful to researchers in vocology.

Electroglottography in Medical Diagnostics of Vocal Tract Pathologies: A Systematic Review

Electroglottography (EGG) is a technology developed for measuring the vocal fold contact area during human voice production. Although considered subjective and unreliable as a sole diagnostic method, with the correct application of relevant computational methods, it can constitute a most promising non-invasive voice disorder diagnostic tools in a form of a digital vocal tract pathology classifier. The aim of the following study is to gather and evaluate currently existing digital voice quality assessment systems and vocal tract abnormality classification systems that rely on the use of electroglottographic bio-impedance signals. To fully comprehend the findings of this review, first the subject of EGG is introduced. For that, we summarise most relevant existing research on EGG with a particular focus on its application in diagnostics. Then, we move on to the focal point of this work, which is describing and comparing the existing EGG-based digital voice pathology classification systems. With the application of PRISMA model, 13 articles were chosen and analysed in detail. Direct comparison between chosen studies brought us to pivotal conclusions, which have been described in Section 5 of this report. Meanwhile, certain limitations arising from the literature were identified, such as questionable understanding of the nature of EGG bio-impedance signals. The appropriate recommendations for future work were made, including the application of different methods for EGG feature extraction, as well as the need for continuous EGG datasets development containing signals gathered in various conditions and with different equipments.

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

INTRODUCTION

Typical 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.

OBJECTIVE

The 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 DESIGN

Cross-sectional study.

METHODS

Aerodynamic 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.

RESULTS

For 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.

CONCLUSIONS

We 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.

Transphonologization of onset voicing: revisiting Northern and Eastern Kmhmu'

Phonation and vowel quality are often thought to play a vital role at the initial stage of tonogenesis. This paper investigates the production of voicing and tones in a tonal Northern Kmhmu' dialect spoken in Nan Province, Thailand, and a non-tonal Eastern Kmhmu' dialect spoken in Vientiane, Laos, from both acoustic and electroglottographic perspectives. Large and consistent VOT differences between voiced and voiceless stops are preserved in Eastern Kmhmu', but are not found in Northern Kmhmu', consistent with previous reports. With respect to pitch, f0 is clearly a secondary property of the voicing contrast in Eastern Kmhmu', but unquestionably the primary contrastive property in Northern Kmhmu'. Crucially, no evidence is found to suggest that either phonation type or formant differences act as significant cues to voicing in Eastern Kmhmu' or tones in Northern Kmhmu'. These results suggests that voicing contrasts can also be transphonologized directly into f0-based contrasts, skipping a registral stage based primarily on phonation and/or vowel quality.

Lip hyper-articulation in loud voice: Effect on resonance-harmonic proximity

Men and women speakers were recorded while producing sustained vowels at comfortable and loud levels. Following comfortable speech, loud levels were produced in three different conditions: first without specific instruction (UL); then maintaining the same pitch as the comfortable level (PL); and finally, keeping both pitch and lip articulation constant (PAL). The sound pressure level, the fundamental frequency ( f_o), the first two vocal tract resonances (R1 and R2), the lip geometry, and the larynx height were measured. For women, a closer proximity of R1 to its nearest harmonic, nf_o, was observed in UL. However, no such increased proximity was found in PL, when speakers could, and did, hyper-articulate. Also, no increased proximity was observed in PAL, when lip articulation was constrained. No significant increase in R1: nf_o proximity was observed in men in any of the three loud conditions. Finally, R2 was not observed significantly closer to a voice harmonic in loud speech, for neither men nor women.

Oral and Laryngeal Articulation Control of Voicing in Children with and without Speech Sound Disorders

Voicing contrast is hard to master during speech motor development, and the phonological process of consonant devoicing is very frequent in children with Speech Sound Disorders (SSD). Therefore, the aim of this study was to characterise the oral and laryngeal articulation control strategies used by children with and without SSD as a function of place of articulation. The articulation rate and relative oral airflow amplitude (flow) were used to analyse how children controlled oral articulation; fundamental frequency (f_o), open quotient (OQ), and a classification of voicing were used to explore laryngeal behaviour. Data from detailed speech and language assessments, oral airflow and electroglottography signals were collected from 13 children with SSD and 17 children without SSD, aged 5; 0 to 7; 8, using picture naming tasks. Articulation rate and flow in children with and without SSD were not significantly different, but a statistically reliable effect of place on flow was found. Children with and without SSD used different relative f_o (which captures changes in f_o during the consonant-vowel transition) and OQ values, and place of articulation had an effect on the strength of voicing. All children used very similar oral articulation control of voicing, but children with SSD used less efficient laryngeal articulation strategies (higher subglottal damping and more air from the lungs expelled in each glottal cycle) than children without SSD.

Northern Raglai voicing and its relation to Southern Raglai register: evidence for early stages of registrogenesis

Northern and Southern Raglai are two closely related Austronesian dialects (Chamic branch) spoken in south-central Vietnam. Although they are mutually intelligible, Northern Raglai is described as having a voicing contrast in onset stops, while Southern Raglai is assumed to have replaced the Chamic voicing contrast with a register contrast realized on the whole syllable (but primarily on its vowel). A production study of the two dialects confirms that Northern Raglai preserves a voicing contrast, even if most women exhibit partial devoicing of their voiced stops, and that Southern Raglai has developed a register contrast based on F1 and phonation cues at the beginning of vowels. The weights of the acoustic properties of voicing and register are similar across ages and genders, suggesting that the two laryngeal contrasts are phonetically stable. Even if there is little evidence of change in progress, a close inspection of the Northern Raglai voicing contrast reveals voicing-conditioned modulations of F1 and perturbations of phonation after partially devoiced stops that could be precursors of a register system similar to that of Southern Raglai. We argue that this is a pathway to registrogenesis and speculate about the articulatory laryngeal mechanisms that could trigger registrogenetic changes. Our data also show that the Northern Raglai voicing contrast is unstable in aspirated stops and that voiced aspirated stops typically have a partially voiceless and partially voiced aspiration.

Towards a Singing Voice Multi-Sensor Analysis Tool: System Design, and Assessment Based on Vocal Breathiness

Singing voice is a human quality that requires the precise coordination of numerous kinetic functions and results in a perceptually variable auditory outcome. The use of multi-sensor systems can facilitate the study of correlations between the vocal mechanism kinetic functions and the voice output. This is directly relevant to vocal education, rehabilitation, and prevention of vocal health issues in educators; professionals; and students of singing, music, and acting. In this work, we present the initial design of a modular multi-sensor system for singing voice analysis, and describe its first assessment experiment on the ‘vocal breathiness’ qualitative characteristic. A system case study with two professional singers was conducted, utilizing signals from four sensors. Participants sung a protocol of vocal trials in various degrees of intended vocal breathiness. Their (i) vocal output, (ii) phonatory function, and (iii) respiratory behavior-per-condition were recorded through a condenser microphone (CM), an Electroglottograph (EGG), and thoracic and abdominal respiratory effort transducers (RET), respectively. Participants’ individual respiratory management strategies were studied through qualitative analysis of RET data. Microphone audio samples breathiness degree was rated perceptually, and correlation analysis was performed between sample ratings and parameters extracted from CM and EGG data. Smoothed Cepstral Peak Prominence (CPPS) and vocal folds’ Open Quotient (OQ), as computed with the Howard method (HOQ), demonstrated the higher correlation coefficients, when analyzed individually. DECOM method-computed OQ (DOQ) was also examined. Interestingly, the correlation coefficient of pitch difference between estimates from CM and EGG signals appeared to be (based on the Pearson correlation coefficient) statistically insignificant (a result that warrants investigation in larger populations). The study of multi-variate models revealed even higher correlation coefficients. Models studied were the Acoustic Breathiness Index (ABI) and the proposed multiple regression model CDH (CPPS, DOQ, and HOQ), which was attempted in order to combine analysis results from microphone and EGG signals. The model combination of ABI and the proposed CDH appeared to yield the highest correlation with perceptual breathiness ratings. Study results suggest potential for the use of a completed system version in vocal pedagogy and research, as the case study indicated system practicality, a number of pertinent correlations, and introduced topics with further research possibilities.

Non-invasive thyroid detection based on electroglottogram signal using machine learning classifiers

Thyroid is a butterfly shaped gland located in the neck region. Hormones are secreted by the thyroid gland that is responsible for various functions that maintain metabolism of the body. The variance in secretion of the hormones causes disorders such as Hyperthyroidism or Hypothyroidism. Electroglottography signal is a bio signal which represents the impedance that exist between the glottis regions. The study aims at design and development of an hardware circuit for the acquisition of Electroglottogram signal from normal and thyroid subjects is proposed followed by feature extraction from the acquired bio signal is performed. Further, machine learning classifiers were used to classify the normal and thyroid individuals. This modality of acquisition is non-invasive. Performance evaluation is done by testing various classifiers to study the accuracy. The classifiers tested were Random Forest, Random Tree, Bayes Net, Multilayer Perceptron, Simple Logistic classifier, and One-R classifier. Classifiers such as Random Forest, Random Tree, and Multilayer Perceptron showed high accuracy. The accuracy estimated by these classifiers was tested and its ROC curves with AUC scores were derived. The highest accuracy was reported for Simple Logistic classifier which was about 95.1%. Random Forest and Random Tree reported 93.5% and 91.9% respectively. Similarly, Multilayer Perceptron and Bayes Net gave 93.5% and 91.9%. The One-R classifier algorithm reported the lowest accuracy of 90.3% among the studied classifier algorithms. The ROC-AUC score for the classifiers were also reported to be more than 0.9 which is considered more promising and supports the acquisition and processing methodology. Hence the proposed technique can be efficiently used to diagnose thyroid non-invasively.

Assessing vowel effects on voice quality, and voice quality effects on the respiratory system

This study assesses (a) effects of vowel height and tense-lax status on the laryngeal closed quotient (CQ) and (b) whether respiratory volume changes vary with differences in CQ. German speakers produced words containing eight different vowels in normal and loud conditions. The only significant vowel effect was found for the /a:-a/ pair, with lower CQ in /a/ at normal intensity. There was an insignificant trend for lower CQ to be associated with more negative thoracic slopes. The CQ difference for the /a:-a/ contrast, which relies more on duration than other tense-lax pairs in German, requires further study.

Identification of glottal instants using electroglottographic signal for vulnerable cases of voicing

Robust detection of glottal instants is essential for various speech and biomedical applications. Glottal closing and glottal opening are two crucial instants/epochs of a glottal cycle. The first-order derivative of the Electroglottographic (EGG) signal demonstrates important peaks at those locations for standard voicing, but the detection of glottal instants becomes erroneous when the peak to peak amplitude of the EGG signal is very low, irregular and unpredictable. In this work, a new efficient method is proposed for identification of glottal instants from the EGG signals including the segments of the signals where the signals are feeble with irregular periodicity. The overall accuracy of detection will be enhanced by identifying the glottal instants for the whole part of the signal including the vulnerable segments of signal. As the phase of a signal is uniform in nature, the phase information of the EGG signal has been explored to detect glottal instants accurately. Under low strength of the EGG signal, the proposed method remarkably has better performance compared to the existing instants detection methods and for pathological EGG signal, the detection accuracy of glottal instants is better than other existing methods.

Vocal Fold Collision Speed in vivo: The Effect of Loudness

Mechanical impact stress on the vocal fold surface, particularly when excessive, has been postulated to cause the so-called phonotraumatic tissue lesions, such as nodules and polyps. The collision stress between the vocal folds depends on the vocal fold velocity at the time of impact. Hence this vocal fold collision speed is a relevant parameter when considering biomechanical economy of phonation, especially in voice professionals needing a louder voice than normal. Combining a precise photometric measurement of glottal area and simultaneous measurements of translaryngeal impedance (electroglottogram) for identifying the time of the maximum rate of increase of vocal fold contact allows computing the vocal fold collision speed in a wide range of loudnesses. The vocal fold collision speed is - for modal voicing - always smaller than the maximum vocal fold velocity during the closing phase, but it strongly increases with intensity. Moreover, this increase shows a biphasic pattern, with a significant enhancement from a certain value of dB on. Understanding physiological variables that influence vocal fold collision forces provides relevant insight into the pathophysiology and the prevention of voice disorders associated with phonotraumatic vocal hyperfunction.

Microsaccadic rate signatures correlate under monocular and binocular stimulation conditions

Microsaccades are involuntary eye movements occurring naturally during fixation. In this study, microsaccades were investigated under monocularly and binocularly stimulated conditions with respect to their directional distribution and rate signature, that refers to a curve reporting the frequency modulation of microsaccades over time. For monocular stimulation the left eye was covered by an infrared filter. In both stimulation conditions, participants fixated a Gabor patch presented randomly in orientation of 45° or 135° over a wide range of spatial frequencies appearing in the center of a monitor. Considering the microsaccadic directions, this study showed microsaccades to be preferably horizontally oriented in their mean direction, regardless of the spatial characteristics of the grating. Furthermore, this outcome was found to be consistent between both stimulation conditions. Moreover, this study found that the microsaccadic rate signature curve correlates between both stimulation conditions, while the curve given for binocular stimulation was already proposed as a tool for estimation of visual performance in the past.

Therefore, this study extends the applicability of microsaccades to clinical use, since parameters as contrast sensitivity, has been measured monocularly in the clinical attitude.

Changes in the voice production of solo singers across concert halls

To investigate the influence of room acoustics on singing, four lyrical singers (soprano, mezzo-soprano, tenor, baritone) performed four musical pieces in eight different venues (from dry studio to reverberant church). In addition to vocal intensity measured by a near-field microphone, glottal behavior (vibratory fundamental frequency and contact quotient) was assessed by electroglottography. Statistical linear mixed models showed that the variance in vocal performance was partly explained by room acoustics. Complementary to previous results on voice musical features influenced by timbre and level of the room's response, voice production parameters were mostly influenced by spatial aspects of the room's response.

Fully automatic segmentation of glottis and vocal folds in endoscopic laryngeal high-speed videos using a deep Convolutional LSTM Network

The objective investigation of the dynamic properties of vocal fold vibrations demands the recording and further quantitative analysis of laryngeal high-speed video (HSV). Quantification of the vocal fold vibration patterns requires as a first step the segmentation of the glottal area within each video frame from which the vibrating edges of the vocal folds are usually derived. Consequently, the outcome of any further vibration analysis depends on the quality of this initial segmentation process. In this work we propose for the first time a procedure to fully automatically segment not only the time-varying glottal area but also the vocal fold tissue directly from laryngeal high-speed video (HSV) using a deep Convolutional Neural Network (CNN) approach. Eighteen different Convolutional Neural Network (CNN) network configurations were trained and evaluated on totally 13,000 high-speed video (HSV) frames obtained from 56 healthy and 74 pathologic subjects. The segmentation quality of the best performing Convolutional Neural Network (CNN) model, which uses Long Short-Term Memory (LSTM) cells to take also the temporal context into account, was intensely investigated on 15 test video sequences comprising 100 consecutive images each. As performance measures the Dice Coefficient (DC) as well as the precisions of four anatomical landmark positions were used. Over all test data a mean Dice Coefficient (DC) of 0.85 was obtained for the glottis and 0.91 and 0.90 for the right and left vocal fold (VF) respectively. The grand average precision of the identified landmarks amounts 2.2 pixels and is in the same range as comparable manual expert segmentations which can be regarded as Gold Standard. The method proposed here requires no user interaction and overcomes the limitations of current semiautomatic or computational expensive approaches. Thus, it allows also for the analysis of long high-speed video (HSV)-sequences and holds the promise to facilitate the objective analysis of vocal fold vibrations in clinical routine. The here used dataset including the ground truth will be provided freely for all scientific groups to allow a quantitative benchmarking of segmentation approaches in future.

Electroglottographic and acoustic analysis of voice in children with vocal nodules

PURPOSE

Vocal fold nodules are usually caused by voice overuse or vocal hyperfunction, and their symptoms include persistent hoarseness - a disturbance in the vocal fold vibrations which results in a turbulent passage of air in the glottis, manifested as a raspy, rough voice. The aim of the study was to present data concerning voice quality in patients with vocal nodules and to compare electroglottographic analysis (EGG) with acoustic analysis.

METHODS

The study examined 57 children with vocal fold nodules (Group 1). Each patient underwent a phoniatric evaluation of the vocal tract, a videolaryngoscopic examination, and a voice quality assessment, employing electroglottographic and acoustic analyses. The control group consisted of 37 healthy children (Group 2). The following parameters were analyzed: Closed Quotient (EGG signal), Peak Slope, Normalized Amplitude Quotient and Cepstral Peak Prominence (acoustic signal - waveform).

RESULTS

Changes in the EGG signal could be detected in 95% of the patients with vocal nodules, indicating the occurrence of vocal nodules and glottal insufficiency. The acoustic analysis confirmed breathy phonation in 63% of the patients. The Closed Quotient parameter proved to be more effective than Peak Slope. Closed Quotient, Peak Slope and Normalized Amplitude Quotient allowed for the differentiation of the EGG signal and the acoustic signal in groups 1 and 2 in a statistically significant way.

CONCLUSIONS

The results of electroglottographic and acoustic analysis show incorrect voice parameters in patients with vocal nodules with reference to the control group. At the same time, the EGG analysis proved to be more effective than the analysis of the acoustic signal.

The effects of age and pitch level on electroglottographic measures during sustained phonation

The aim of the present study was to use electroglottography (EGG) to explore the effects of age and pitch level on sustained vowel phonation. Thirty female individuals (10 young, 10 middle-aged, and 10 older speakers) without voice disorders or training in singing participated in this study. Eight EGG parameters were measured during sustained vowel production with a high, mid, or low pitch: fundamental frequency, contact quotient, contacting-time quotient, decontacting-time quotient, speed quotient with a midslope criterion (SQ-mid), jitter, shimmer, and the harmonics-to-noise ratio. Age was found to be a significant factor in fundamental frequency, contact quotient, contacting-time quotient, decontacting-time quotient, and SQ-mid. With increasing age, the mean fundamental frequency decreased while the contact quotient increased. The middle-aged and older speakers had more asymmetrical vocal fold vibratory patterns than the young speakers. As for pitch level, the high pitch had a significantly less decontacting-time quotient and greater SQ-mid than low and mid pitches. The lack of significant interaction between age and pitch level indicates that the effects of age and pitch level could be additive. Finally, the discriminant analyses show that contact quotient is an important factor in predicting the age of a voice.

Estimation of Source-Filter Interaction Regions Based on Electroglottography

Source-filter interaction is a phenomenon in which acoustic airway pressures influence the glottal airflow at the source (level 1) and the vibration pattern of the vocal folds (level 2). This interaction is most significant when dominant source harmonics are near airway resonances. The influence of acoustic airway pressures on vocal fold vibration (level 2) was studied systematically by changing the supraglottal vocal tract length in human subjects with tube extensions. The subjects were asked to perform fundamental frequency (fo) glides while phonating through tubes of various lengths. An algorithm was developed using the quasi-open quotient extracted from the electroglottograph. Regions of sudden vocal fold vibration pattern change due to source-filter interaction were inferred from contact area changes. The algorithm correctly identified 89% of male and 84.8% of female quantal changes in contact pattern associated with interactions between source harmonics and formants during ascending glides. During the descending glides, the algorithm correctly identified 84% of male and 81.1% of female quantal changes in contact pattern. These results are in comparison with those obtained from the fo-based algorithm (Maxfield et al).

Automatic real-time gait event detection in children using deep neural networks

Annotation of foot-contact and foot-off events is the initial step in post-processing for most quantitative gait analysis workflows. If clean force plate strikes are present, the events can be automatically detected. Otherwise, annotation of gait events is performed manually, since reliable automatic tools are not available. Automatic annotation methods have been proposed for normal gait, but are usually based on heuristics of the coordinates and velocities of motion capture markers placed on the feet. These heuristics do not generalize to pathological gait due to greater variability in kinematics and anatomy of patients, as well as the presence of assistive devices. In this paper, we use a data-driven approach to predict foot-contact and foot-off events from kinematic and marker time series in children with normal and pathological gait. Through analysis of 9092 gait cycle measurements we build a predictive model using Long Short-Term Memory (LSTM) artificial neural networks. The best-performing model identifies foot-contact and foot-off events with an average error of 10 and 13 milliseconds respectively, outperforming popular heuristic-based approaches. We conclude that the accuracy of our approach is sufficient for most clinical and research applications in the pediatric population. Moreover, the LSTM architecture enables real-time predictions, enabling applications for real-time control of active assistive devices, orthoses, or prostheses. We provide the model, usage examples, and the training code in an open-source package.

A comparison of electroglottographic and glottal area waveforms for phonation type differentiation in male professional singers

This study compares the use of electroglottograms (EGGs) and glottal area waveforms (GAWs) to study phonation in different vibratory states as produced by professionally trained singers. Six western classical tenors were asked to phonate pitch glides from modal to falsetto phonation, or from modal to their stage voice above the passaggio (SVaP). For each pitch glide the sample entropy (SampEn) of the EGG signal was calculated to detect the occurrence of phonatory instabilities and establish a "ground truth" for the performed phonation type. The cycles before the maximum SampEn were labeled as modal, and the cycles after the peak were labeled as either falsetto, or SVaP. Three automatic categorizations of vibratory state were performed using clustering: one based only on the EGG, one based on the GAW, and one based on their combination. The error rate (clustering vs ground truth) was, on average, lower than 10% for all of the three settings, revealing no special advantage of the GAW over EGG, and vice versa. Modal voice cycles exhibited a larger contact quotient, larger normalized derivative peak ratio, and lower rise time, compared to SVaP and falsetto. The GAW-based normalized maximum area declination rate was larger in SVaP compared to modal voice.

Paradigmatic variation of vowels in expressive speech: Acoustic description and dimensional analysis

Acoustic variation in expressive speech at the syllable level is studied. As emotions or attitudes can be conveyed by short spoken words, analysis of paradigmatic variations in vowels is an important issue to characterize the expressive content of such speech segments. The corpus contains 160 sentences produced under seven expressive conditions (Neutral, Anger, Fear, Surprise, Sensuality, Joy, Sadness) acted by a French female speaker (a total of 1120 sentences, 13 140 vowels). Eleven base acoustic parameters are selected for voice source and vocal tract related feature analysis. An acoustic description of the expressions is drawn, using the dimensions of melodic range, intensity, noise, spectral tilt, vocalic space, and dynamic features. The first three functions of a discriminant analysis explain 95% of the variance in the data. These statistical dimensions are consistently associated with acoustic dimensions. Covariation of intensity and F0 explains over 80% of the variance, followed by noise features (8%), covariation of spectral tilt, and F0 (7%). On the basis of isolated vowels alone, expressions are classified with a mean accuracy of 78%.

Investigating the Voce Faringea: Physiological and Acoustic Characteristics of the Bel Canto Tenor's Forgotten Singing Practice

Several historical sources from the first half of the 19th century mention a distinct third register mechanism particular to tenor voices of that period. This so-called voce faringea-often described as an "intermediate" register-is a virtually forgotten historical singing practice used to extend the upper range of the voice, where the singer modifies falsetto, typically a weak and often feminine sound, into a more powerful, tenor-like vocal quality. Based on an evaluation of historical voice register theories, training strategies, and the sound ideals of the historical period, an informed discussion of that technique is developed. For this study, acoustic and electroglottographic signals for tones produced on the vowel /a/ by a professional tenor/countertenor in different vocal register mechanisms-voce faringea, falsetto, chest register, and mezza voce-were recorded using the VoceVista system. Analysis of the electroglottography (EGG) and audio data revealed specific characteristics of the voce faringea with regard to both the laryngeal mechanism and the sound spectrum, including high EGG contact quotient and low speed quotient values. EGG pulses were skewed significantly to the left and displayed a distinct knee shape during the de-contacting phase of the vocal folds, which consequently indicates a vibration with a clear mucosal wave. The long-term average spectrum and power spectrum exposed a considerable amplification and dislocation of F₂ in the direction of high frequencies, thus boosting the third harmonic and showing a strong concentration of acoustic energy in the area of the singer's formant cluster.

Physiological and acoustic characteristics of the male music theatre voice

Six male music theatre singers were recorded in three different voice qualities: legit and two types of belt ("chesty" and "twangy"), on two vowels ([e] and [ɔ]), at four increasing pitches in the upper limit of each singer's belt range (∼250-440 Hz). The audio signal, the electroglottographic (EGG) signal, and the vocal tract impedance were all measured simultaneously. Voice samples were analyzed and then evaluated perceptually by 16 expert listeners. The three qualities were produced with significant differences at the physiological, acoustical, and perceptual levels: Singers produced belt qualities with a higher EGG contact quotient (CQEGG) and greater contacting speed quotient (Qcs), greater sound pressure level (SPL), and energy above 1 kHz (alpha ratio), and with higher frequencies of the first two vocal tract resonances (fR1, fR2), especially in the upper pitch range when compared to legit. Singers produced the chesty belt quality with higher CQEGG, Qcs, and SPL values and lower alpha ratios over the whole belt range, and with higher fR1 at the higher pitch range when compared to twangy belt. Consistent tuning of fR1 to the second voice harmonic (2f0) was observed in all three qualities and for both vowels. Expert listeners tended to identify all qualities based on the same acoustical and physiological variations as those observed in the singers' intended qualities.

A Measure of the Auditory-perceptual Quality of Strain from Electroglottographic Analysis of Continuous Dysphonic Speech: Application to Adductor Spasmodic Dysphonia

OBJECTIVES

(1) To develop an automated algorithm to analyze electroglottographic (EGG) signal in continuous dysphonic speech, and (2) to identify EGG waveform parameters that correlate with the auditory-perceptual quality of strain in the speech of patients with adductor spasmodic dysphonia (ADSD).

STUDY DESIGN

Software development with application in a prospective controlled study.

METHODS

EGG was recorded from 12 normal speakers and 12 subjects with ADSD reading excerpts from the Rainbow Passage. Data were processed by a new algorithm developed with the specific goal of analyzing continuous dysphonic speech. The contact quotient, pulse width, a new parameter peak skew, and various contact closing slope quotient and contact opening slope quotient measures were extracted. EGG parameters were compared between normal and ADSD speech. Within the ADSD group, intra-subject comparison was also made between perceptually strained syllables and unstrained syllables.

RESULTS

The opening slope quotient SO7525 distinguished strained syllables from unstrained syllables in continuous speech within individual subjects with ADSD. The standard deviations, but not the means, of contact quotient, EGGW50, peak skew, and SO7525 were different between normal and ADSD speakers. The strain-stress pattern in continuous speech can be visualized as color gradients based on the variation of EGG parameter values.

CONCLUSIONS

EGG parameters may provide a within-subject measure of vocal strain and serve as a marker for treatment response. The addition of EGG to multidimensional assessment may lead to improved characterization of the voice disturbance in ADSD.

Ensuring safety and functionality of electroglottography measurements during dynamic pulmonary MRI

PURPOSE

To combine vocal tract measurements with dynamic MRI of the lungs to provide fundamental insights into the lung physiology during singing.

METHODS

To analyze vocal fold oscillatory patterns during dynamic lung MRI, an electroglottography (EGG) system was modified to allow for simultaneous EGG measurements during MR image acquisitions. A low-pass filter was introduced to suppress residual radiofrequency (RF) coupling into the EGG signal. RF heating was tested in a gel phantom to ensure MR safety, and functionality of the EGG device was assessed in a volunteer experiment at singing frequencies from A5 to A3. In the recorded EGG signals, remaining RF interferences were removed by independent component analysis post processing, and standard EGG parameters such as fundamental frequency, contact quotient and jitter were calculated. In a second volunteer experiment, EGG recordings were compared with lung diameter measurements from 2D time-resolved trueFISP acquisitions.

RESULTS

RF heating measurements resulted in less than 1.2°C temperature increase in the gel phantom. EGG parameters measured during MR imaging are within the range of ideal values. In the lung measurement, both the lung diameter and the EGG recordings could be successfully performed with only minimal interference.

CONCLUSION

EGG recording is pos sible during dynamic lung MRI, and glottal activity can be studied safely at 1.5T. Magn Reson Med 76:1629-1635, 2016. © 2015 International Society for Magnetic Resonance in Medicine.

Comparing Vocal Fold Contact Criteria Derived From Audio and Electroglottographic Signals

OBJECTIVES

Collision threshold pressure (CTP), that is, the lowest subglottal pressure facilitating vocal fold contact during phonation, is likely to reflect relevant vocal fold properties. The amplitude of an electroglottographic (EGG) signal or the amplitude of its first derivative (dEGG) has been used as criterion of such contact. Manual measurement of CTP is time consuming, making the development of a simpler, alternative method desirable.

METHOD

In this investigation, we compare CTP values measured manually to values automatically derived from dEGG and to values derived from a set of alternative parameters, some obtained from audio and some from EGG signals. One of the parameters was the novel EGG wavegram, which visualizes sequences of EGG or dEGG cycles, normalized with respect to period and amplitude. Raters with and without previous acquaintance with EGG analysis marked the disappearance of vocal fold contact in dEGG and in wavegram displays of /pa:/-sequences produced with continuously decreasing vocal loudness by seven singer subjects.

RESULTS

Vocal fold contact was mostly identified accurately in displays of both dEGG amplitude and wavegram. Automatically derived CTP values showed high correlation with those measured manually and with those derived from the ratings of the visual displays. Seven other parameters were tested as criteria of such contact. Mainly, because of noise in the EGG signal, most of them yielded CTP values differing considerably from those derived from the manual and the automatic methods, although the EGG spectrum slope showed a high correlation.

CONCLUSION

The possibility of measuring CTP automatically seems promising for future investigations.

Glottal Adduction and Subglottal Pressure in Singing

Previous research suggests that independent variation of vocal loudness and glottal configuration (type and degree of vocal fold adduction) does not occur in untrained speech production. This study investigated whether these factors can be varied independently in trained singing and how subglottal pressure is related to average glottal airflow, voice source properties, and sound level under these conditions. A classically trained baritone produced sustained phonations on the endoscopic vowel [i:] at pitch D4 (approximately 294 Hz), exclusively varying either (a) vocal register; (b) phonation type (from "breathy" to "pressed" via cartilaginous adduction); or (c) vocal loudness, while keeping the others constant. Phonation was documented by simultaneous recording of videokymographic, electroglottographic, airflow and voice source data, and by percutaneous measurement of relative subglottal pressure. Register shifts were clearly marked in the electroglottographic wavegram display. Compared with chest register, falsetto was produced with greater pulse amplitude of the glottal flow, H1-H2, mean airflow, and with lower maximum flow declination rate (MFDR), subglottal pressure, and sound pressure. Shifts of phonation type (breathy/flow/neutral/pressed) induced comparable systematic changes. Increase of vocal loudness resulted in increased subglottal pressure, average flow, sound pressure, MFDR, glottal flow pulse amplitude, and H1-H2. When changing either vocal register or phonation type, subglottal pressure and mean airflow showed an inverse relationship, that is, variation of glottal flow resistance. The direct relation between subglottal pressure and airflow when varying only vocal loudness demonstrated independent control of vocal loudness and glottal configuration. Achieving such independent control of phonatory control parameters would be an important target in vocal pedagogy and in voice therapy.

Vocal Qualities in Music Theater Voice: Perceptions of Expert Pedagogues

OBJECTIVES/HYPOTHESIS

To gather qualitative descriptions of music theater vocal qualities including belt, legit, and mix from expert pedagogues to better define this voice type.

STUDY DESIGN

This is a prospective, semistructured interview.

METHODS

Twelve expert teachers from United States, United Kingdom, Asia, and Australia were interviewed by Skype and asked to identify characteristics of music theater vocal qualities including vocal production, physiology, esthetics, pitch range, and pedagogical techniques. Responses were compared with published studies on music theater voice.

RESULTS

Belt and legit were generally described as distinct sounds with differing physiological and technical requirements. Teachers were concerned that belt should be taught "safely" to minimize vocal health risks. There was consensus between teachers and published research on the physiology of the glottis and vocal tract; however, teachers were not in agreement about breathing techniques. Neither were teachers in agreement about the meaning of "mix." Most participants described belt as heavily weighted, thick folds, thyroarytenoid-dominant, or chest register; however, there was no consensus on an appropriate term. Belt substyles were named and generally categorized by weightedness or tone color. Descriptions of male belt were less clear than for female belt.

CONCLUSIONS

This survey provides an overview of expert pedagogical perspectives on the characteristics of belt, legit, and mix qualities in the music theater voice. Although teacher responses are generally in agreement with published research, there are still many controversial issues and gaps in knowledge and understanding of this vocal technique. Breathing techniques, vocal range, mix, male belt, and vocal registers require continuing investigation so that we can learn more about efficient and healthy vocal function in music theater singing.

Voice Register in Mon: Acoustics and Electroglottography

Mon is spoken in villages in Thailand and Myanmar. The dialect of Ban Nakhonchum, Thailand, has 2 voice registers, modal and breathy; these phonation types, along with other phonetic properties, distinguish minimal pairs. Four native speakers of this dialect recorded repetitions of 14 randomized words (7 minimal pairs) for acoustic analysis. We used a subset of these pairs in a listening test to verify the perceptual robustness of the register distinction. Acoustic analysis found significant differences in noise component, spectral slope and fundamental frequency. In a subsequent session 4 speakers were also recorded using electroglottography, which showed systematic differences in the contact quotient. The salience of these properties in maintaining the register distinction is discussed in the context of possible tonogenesis for this language.

Contact quotient versus closed quotient: a comparative study on professional male singers

OBJECTIVES

The term "closed quotient" is frequently used for data derived both from inverse filtering and from electroglottography. In the former case, it is defined as the ratio between the closed phase and the period, as measured in flow glottograms (FLOGG), whereas in the latter case, it is defined as the time interval between the falling and rising parts of the electroglottogram (EGG), measured at some percentage of the peak-to-peak amplitude. The study aims at analyzing differences between EGG- and FLOGG-based closed quotients and their relationships with voice source parameters.

STUDY DESIGN

Comparative study.

METHODS

FLOGG- and EGG-based measures collected from five professional male singers were compared, under different pitch and loudness conditions.

RESULTS

Compared with the FLOGG-based quotient, the EGG-based quotient (i) varied more between subjects, (ii) presented greater values, (iii) varied less with subglottal pressure, (iv) varied less with the normalized amplitude quotient (ie, the ratio between the flow pulse amplitude and the product of period and maximum flow declination rate), and (v) varied less with the relative amplitude of the voice source fundamental.

CONCLUSIONS

Although positively related, FLOGG- and EGG-based closed quotients differ and must not be confused.