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.

Domestic cat larynges can produce purring frequencies without neural input

Most mammals produce vocal sounds according to the myoelastic-aerodynamic (MEAD) principle, through self-sustaining oscillation of laryngeal tissues.1,2 In contrast, cats have long been believed to produce their low-frequency purr vocalizations through a radically different mechanism involving active muscle contractions (AMC), where neurally driven electromyographic burst patterns (typically at 20-30 Hz) cause the intrinsic laryngeal muscles to actively modulate the respiratory airflow. Direct empirical evidence for this AMC mechanism is sparse.3 Here, the fundamental frequency (fo) ranges of eight domestic cats (Felis silvestris catus) were investigated in an excised larynx setup, to test the prediction of the AMC hypothesis that vibration should be impossible without neuromuscular activity, and thus unattainable in excised larynx setups, which are based on MEAD principles. Surprisingly, all eight excised larynges produced self-sustained oscillations at typical cat purring rates. Histological analysis of cat larynges revealed the presence of connective tissue masses, up to 4 mm in diameter, embedded in the vocal fold.4 This vocal fold specialization appears to allow the unusually low fo values observed in purring. While our data do not fully reject the AMC hypothesis for purring, they show that cat larynges can easily produce sounds in the purr regime with fundamental frequencies of 25 to 30 Hz without neural input or muscular contraction. This strongly suggests that the physical and physiological basis of cat purring involves the same MEAD-based mechanisms as other cat vocalizations (e.g., meows) and most other vertebrate vocalizations but is potentially augmented by AMC.

Near-infrared photoglottography for measuring multiple glottal events

Near-infrared (NIR) photoglottography (PGG) is a non-invasive method for monitoring glottal activities which retains functionality of conventional PGG using visible light with more convenient accessibility. This paper is to investigate its performance in comparison with simultaneously recorded electroglottography (EGG) signals. Results showed that NIR PGG detects continuous transillumination for glottal aperture and vocal-fold contact. Glottal timing markers known as glottal closure and opening instants are detectable agreeing to the corresponding EGG-based instants. Further, it was inferred that variations of glottal waveforms based on NIR PGG reflect vertical vocal-fold edge motions.

Application of the HRES 5562 Camera Using the HSDI Technique in the Diagnosis of Glottal Insufficiencies in Teachers

OBJECTIVE

Teachers are the largest group of professional voice users with predispositions to functional or organic changes in the larynx. The dysfunction of intrinsic muscles of the larynx frequently occurs which leads to changes in parameters of quality of voice (dysphonia). The aim of the study is the assessment of parameters of vocal folds vibrations, Mucosal Wave morphology, Glottal Closure Type and Open Quotient (OQ) using High Speed (HS) camera and High Speed Digital Imaging (HSDI) technique in teachers with disorders of voice quality classified in GRBAS scale in glottal insufficiencies.

MATERIAL AND METHOD

The study included group of 50 teachers of both genders, working in primary and secondary education units for 15 years, without systemic diseases with disorders of quality of voice confirmed by the results in GRBAS scale assessment. Vocal folds vibrations were assessed with HS camera by R. Wolf and HSDI technique. Rigid endoscope with 90^o optics by the same company was used in the study. Vocal folds vibrations were registered with the speed of 4000 frames/sec. Regularity, symmetry of vibrations, Mucosal Wave (MW) morphology as well as Glottal Closure Type were assessed. Numerical value of OQ was determined in anterior, middle and posterior segment of the glottis during phonation.

RESULTS

Assessment of real vibrations of vocal folds revealed irregularity, mean asymmetry of vibrations, MW reduction as well as glottal insufficiency, the most frequently (96%), in the middle segment - type E according to European Laryngological Society, less frequently (4%) - type E+C. The highest value of OQ (average 0.98) was registered in the middle segment of the glottis. In GRBAS scale, significant dysphonia has been registered, classified as G₃R₃B₃A₃ without the features of voice strain - S₀.

CONCLUSION

In group of teachers with extensive professional experience, glottal insufficiency in the middle segment was registered the most frequently which was confirmed by high values of OQ in this region obtained with HSDI technique. What is more, irregularity, mean asymmetry and asynchrony of vibrations with MW reduction were registered which confirmed the existence of glottal insufficiency in this group. GRBAS scale was useful in preliminary evaluation of dysphonia and its severity, however, the diagnosis of its clinical form was possible only with visualization of the larynx and objective parameters obtained with HSDI.

Waveform Amplitude and Temporal Symmetric/Asymmetric Characteristics of Phoneme and Syllable Segments in the W-1 Spondaic Words Recorded by Four Speakers

BACKGROUND

The amplitude and temporal asymmetry of the speech waveform are mostly associated with voiced speech utterances and are obvious in recent graphic depictions in the literature. The asymmetries are attributed to the presence and interactions of the major formants characteristic of voicing with possible contributions from the unidirectional air flow that accompanies speaking.

PURPOSE

This study investigated the amplitude symmetry/asymmetry characteristics (polarity) of speech waveforms that to our knowledge have not been quantified.

STUDY SAMPLE

Thirty-six spondaic words spoken by two male speakers and two female speakers were selected because they were multisyllabic words providing a reasonable sampling of speech sounds and four recordings were available that were not related to the topic under study.

RESEARCH DESIGN

Collectively, the words were segmented into phonemes (vowels [130], diphthongs [77], voiced consonants [258], voiceless consonants [219]), syllables (82), and blends (6). For each segment the following were analyzed separately for the positive and negative datum points: peak amplitude, the percent of the total segment datum points, the root-mean-square (rms) amplitude, and the crest factor.

DATA COLLECTION AND ANALYSES

The digitized words (44,100 samples/s; 16-bit) were parsed into 144 files (36 words × 4 speakers), edited, transcribed to numeric values (±1), and stored in a spread sheet in which all analyses were performed with in-house routines. Overall approximately 85% of each waveform was analyzed, which excluded portions of silent intervals, transitions, and diminished waveform endings.

RESULTS

The vowel, diphthong, and syllable segments had durations (180-220 ms) that were about twice as long as the consonant durations (∼90 ms) and peak and rms amplitudes that were 6 to 12 dB higher than the consonant peak and rms amplitudes. Vowel, diphthong, and syllable segments had 10% more positive datum points (55%) than negative points (45%), which suggested temporal asymmetries within the segments. With voiced consonants, the distribution of positive and negative datum points dropped to 52 and 48% and essentially was equal with the voiceless consonants (50.3 and 49.6%). The mean rms amplitudes of the negative datum points were higher than the rms amplitudes for the positive points by 2 dB (vowels, diphthongs, and syllables), 1 dB (voiced consonants), and 0.1 dB (voiceless consonants). The 144 waveforms and segmentations are illustrated in the Supplementary Material along with the tabularized positive and negative segment characteristics.

CONCLUSIONS

The temporal and amplitude waveform asymmetries were by far most notable in segments that had a voicing component, which included the voiced consonants. These asymmetries were characterized by larger envelopes and more energy in the negative side of the waveform segment than in the positive side. Interestingly, these segments had more positive datum points than negative points, which indicated temporal asymmetry. All aspects of the voiceless consonants were equally divided between the positive and negative domains. There were female/male differences but with these limited samples such differences should not be generalized beyond the speakers in this study. The influence of the temporal and amplitude asymmetries on monaural word-recognition performance is thought to be negligible.

Integrative Insights into the Myoelastic-Aerodynamic Theory and Acoustics of Phonation. Scientific Tribute to Donald G. Miller

In this tribute article to D.G. Miller, we review some historical and recent contributions to understanding the myoelastic-aerodynamic (MEAD) theory of phonation and the related acoustic phenomena in subglottal and vocal tract. At the time of the formulation of MEAD by van den Berg in late 1950s, it was assumed that vocal fold oscillations are self-sustained thanks to increased subglottal pressure pushing the glottis to open and decreased subglottal pressure allowing the glottis to close. In vivo measurements of subglottal pressures during phonation invalidated these assumptions, however, and showed that at low fundamental frequencies subglottal pressure rather tends to reach a maximum value at the beginning of glottal closure and then exhibits damped oscillations. These events can be interpreted as transient acoustic resonance phenomena in the subglottal tract that are triggered by glottal closure. They are analogous to the transient acoustic phenomena seen in the vocal tract. Rather than subglottal pressure oscillations, a more efficient mechanism of transfer of aerodynamic energy to the vocal fold vibrations has been identified in the vertical phase differences (mucosal waves) making the glottal shape more convergent during glottis opening than during glottis closing. Along with other discoveries, these findings form the basis of our current understanding of MEAD.

Rethinking glottal midline detection

A healthy voice is crucial for verbal communication and hence in daily as well as professional life. The basis for a healthy voice are the sound producing vocal folds in the larynx. A hallmark of healthy vocal fold oscillation is the symmetric motion of the left and right vocal fold. Clinically, videoendoscopy is applied to assess the symmetry of the oscillation and evaluated subjectively. High-speed videoendoscopy, an emerging method that allows quantification of the vocal fold oscillation, is more commonly employed in research due to the amount of data and the complex, semi-automatic analysis. In this study, we provide a comprehensive evaluation of methods that detect fully automatically the glottal midline. We used a biophysical model to simulate different vocal fold oscillations, extended the openly available BAGLS dataset using manual annotations, utilized both, simulations and annotated endoscopic images, to train deep neural networks at different stages of the analysis workflow, and compared these to established computer vision algorithms. We found that classical computer vision perform well on detecting the glottal midline in glottis segmentation data, but are outperformed by deep neural networks on this task. We further suggest GlottisNet, a multi-task neural architecture featuring the simultaneous prediction of both, the opening between the vocal folds and the symmetry axis, leading to a huge step forward towards clinical applicability of quantitative, deep learning-assisted laryngeal endoscopy, by fully automating segmentation and midline detection.

Indicators of anterior-posterior phase difference in glottal opening measured from natural production of vowels

Voiced speech is generated by the glottal flow interacting with vocal fold vibrations. However, the details of vibrations in the anterior-posterior direction (the so-called zipper-effect) and their correspondence with speech and other glottal signals are not fully understood due to challenges in direct measurements of vocal fold vibrations. In this proof-of-concept study, the potential of four parameters extracted from high-speed videoendoscopy (HSV), electroglottography, and speech signals to indicate the presence of a zipper-type glottal opening is investigated. Comparison with manual labeling of the HSV videos highlighted the importance of multiple parameter-signal pairs in indicating the presence of a zipper-type glottal opening.

Laryngeal Image Processing of Vocal Folds Motion

This review provides a comprehensive compilation, from a digital image processing point of view of the most important techniques currently developed to characterize and quantify the vibration behaviour of the vocal folds, along with a detailed description of the laryngeal image modalities currently used in the clinic. The review presents an overview of the most significant glottal-gap segmentation and facilitative playbacks techniques used in the literature for the mentioned purpose, and shows the drawbacks and challenges that still remain unsolved to develop robust vocal folds vibration function analysis tools based on digital image processing.

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.

Glottal Closure in Women with No Voice Complaints or Laryngeal Disorders

Introduction  The understanding of normal vocal production is essential to guide any voice professional as it is fundamental to understand the effects of the posterior glottal gap on the vocal quality. Objective  The aim of the present study was to verify the association between glottic closure, acoustic parameters, and some characteristics of the videolaryngostroboscopy of young women without vocal complaints nor laryngeal disorders. Methods  This is a cross-sectional study with 56 women between 20 and 30 years old who underwent videolaryngostroboscopy. The acoustic parameters of the vowel /a:/ were analyzed using the Praat software, Release 4.6.10 (Paul Boersman and David Weenik, Amsterdam, Netherlands). Statistical Analysis  The chi-squared, Fischer, and Kruskall-Wallis tests were applied, with 5% significance. Results  Significant occurrence of posterior glottal gap (85.71%, p  < 0.001), of normal vocal folds vibration amplitude (82.14%, p  < 0.001), and of absence of significant constriction of the laryngeal vestibule (98.21%, p  < 0.001); no significant association of the glottic closure with the vocal acoustic parameters; no significant association of glottic closure, vocal folds vibration amplitude, and constriction of the laryngeal vestibule. Conclusion  There was a predominance of posterior glottal gap, normal vocal folds vibration amplitude, and absence of laryngeal vestibule constriction, and no relation with the acoustic parameters, suggesting that the posterior glottal gap did not generate impact on the vocal production of the young adult women studied.

Impact of Subharmonic and Aperiodic Laryngeal Dynamics on the Phonatory Process Analyzed in Ex Vivo Rabbit Models

Normal voice is characterized by periodic oscillations of the vocal folds. On the other hand, disordered voice dynamics (e.g., subharmonic and aperiodic oscillations) are often associated with voice pathologies and dysphonia. Unfortunately, not all investigations may be conducted on human subjects; hence animal laryngeal studies have been performed for many years to better understand human phonation. The rabbit larynx has been shown to be a potential model of the human larynx. Despite this fact, only a few studies regarding the phonatory parameters of rabbit larynges have been performed. Further, to the best of our knowledge, no ex vivo study has systematically investigated phonatory parameters from high-speed, audio and subglottal pressure data with irregular oscillations. To remedy this, the present study analyzes experiments with sustained phonation in 11 ex vivo rabbit larynges for 51 conditions of disordered vocal fold dynamics. (1) The results of this study support previous findings on non-disordered data, that the stronger the glottal closure insufficiency is during phonation, the worse the phonatory characteristics are; (2) aperiodic oscillations showed worse phonatory results than subharmonic oscillations; (3) in the presence of both types of irregular vibrations, the voice quality (i.e., cepstral peak prominence) of the audio and subglottal signal greatly deteriorated compared to normal/periodic vibrations. In summary, our results suggest that the presence of both types of irregular vibration have a major impact on voice quality and should be considered along with glottal closure measures in medical diagnosis and treatment.

Comparison of electroglottographic variability index in euphonic and pathological voice

In a recent study we introduced a new approach for analysis of the electroglottographic (ECG) signal. This method is based on the evaluation of variation of the EGG signal and its first derivative, through new software developed by the Pisan phoniatric school. This software is designed to extract quantitative indices related to the contacting and decontacting phases of the vocal folds during phonation. The software allows us to study the combined variability of vibration amplitude and velocity (i.e. the first derivative of the EGG signal). Pathological voices show a much more variable EGG signal compared to normal voices, since cordal vibration is made irregular due to the presence of glottis plane pathologies. With the aim of demonstrating the differences between normal and pathological voices relevant to combined vibration amplitude and velocity variability, we have introduced a new quantitative parameter named “variability index, VI”. We studied 95 subjects (35 normal and 60 with pathological voice); among pathologic subjects, 15 showed functional dysphonia and 45 showed organic dysphonia. Subjects affected by organic dysphonia presented: 15 bilateral vocal nodules, 15 unilateral polyps and 15 unilateral cysts. All subjects were studied with videolaryngostroboscopy; electro-acoustic parameters of the voice were analysed with the KayPENTAX CSL (Model 4500) system. The EGG signal was recorded using KAY Model 6103 connected to the CSL system. The new software for the analysis of the EGG signal allows us to obtain not only a VI total value relevant to variability during all the recording, but also partial VI values relevant to the different glottis cycle phases. In fact, plotting the amplitude variation and its first derivative on a Lissajous graph, it is possible to divide the whole glottis cycle into four phases (each represented by four quadrants on the graph): the initial vocal folds contacting activity (VI-Q1), the last phase of vocal folds contacting (VI-Q2), the first phase of vocal folds decontacting (VI-Q3) and the last phase, up to the complete decontacting of vocal folds (VI-Q4). For each quadrant, it is also possible to work out the percent variability index. By comparing the variability indices in the normal and pathological groups, we obtained the following results: the total VI was significantly higher in the pathological subjects (0.25 vs 0.18; p = 0.01); the absolute value of VI was higher in pathological subjects, although the difference was not significant (VI-Q2, 0.041 vs 0.029; VI-Q3, 0.065 vs 0.058; VI-Q4, 0.054 vs 0.052). The percent variability in the Q2 quadrant (VI-Q2%) was significantly higher in pathological subjects compared to normal subjects (0.22 vs 0.16) (p = 0.01). The results of this study confirm that our new software for analysis of EGG signal can distinguish normal voice from pathological voice based on the new quantitative parameter VI. Moreover, this study emphasises that the final contact phase of vocal folds is the most representative of the difference between the normal and pathological voice and shows a wider variability in terms of amplitude and vibration velocity. Further studies on larger groups of subjects will be required to confirm these results and assess differences in the EGG signal among the various vocal fold pathologies.

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.

Quantifying syringeal dynamics in vitro using electroglottography

The complex and elaborate vocalizations uttered by many of the 10,000 extant bird species are considered a major driver in their evolutionary success, warranting study of the underlying mechanisms of vocal production. Additionally, birdsong has developed into a highly productive model system for vocal imitation learning and motor control, where, in contrast to humans, we have experimental access to the entire neuromechanical control loop. In human voice production, complex laryngeal geometry, vocal fold tissue properties, airflow and laryngeal musculature all interact to ultimately control vocal fold kinematics. Quantifying vocal fold kinematics is thus critical to understanding neuromechanical control of voiced sound production, but in vivo imaging of vocal fold kinematics in birds is experimentally challenging. Here, we adapted and tested electroglottography (EGG) as a novel tool for examining vocal fold kinematics in the avian vocal organ, the syrinx. We furthermore imaged and quantified syringeal kinematics in the pigeon (Columba livia) syrinx with unprecedented detail. Our results show that EGG signals predict (1) the relative amount of contact between the avian equivalent of vocal folds and (2) essential parameters describing vibratory kinematics, such as fundamental frequency, and timing of syringeal opening and closing events. As such, EGG provides novel opportunities for measuring syringeal vibratory kinematic parameters in vivo Furthermore, the opportunity for imaging syringeal vibratory kinematics from multiple planar views (horizontal and coronal) simultaneously promotes birds as an excellent model system for studying kinematics and control of voiced sound production in general, including in humans and other mammals.

Investigation of phonatory characteristics using ex vivo rabbit larynges

Quantitative analysis of phonatory characteristics of rabbits has been widely neglected. However, preliminary studies established the rabbit larynx as a potential model of human phonation. This study reports quantitative data on phonation using ex vivo rabbit larynx models to achieve more insight into dependencies of three main components of the phonation process, including airflow, vocal fold dynamics, and the acoustic output. Sustained phonation was induced in 11 ex vivo rabbit larynges. For 414 phonatory conditions, vocal fold vibrations, acoustic, and aerodynamic parameters were analyzed as functions of longitudinal vocal fold pre-stress, applied air flow, and glottal closure insufficiency. Dimensions of the vocal folds were measured and histological data were analyzed. Glottal closure characteristics improved for increasing longitudinal pre-stress and applied airflow. For the subglottal pressure signal only the cepstral peak prominence showed dependency on glottal closure. In contrast, vibrational, acoustic, and aerodynamic parameters were found to be highly dependent on the degree of glottal closure: The more complete the glottal closure during phonation, the better the aerodynamic and acoustic characteristics. Hence, complete or at least partial glottal closure appears to enhance acoustic signal quality. Finally, results validate the ex vivo rabbit larynx as an effective model for analyzing the phonatory process.

Aerodynamic, eletroglottographic and acoustic measures of the voiced postalveolar fricative

PURPOSE

Describe and correlate phonological and complementary measures regarding aerodynamics, electroglottography, acoustics, and perceptual judgment of production of the voiced fricative sound /ʒ/ comparing the performance of Brazilian Portuguese-speaking children with and without speech sound disorders.

METHODS

Study participants were 30 children aged 5 years to 7 years and 11 months divided into a group of children with typical development - Control Group (CG) and a group of children with speech sound disorders - Research Group (RG). Phonology (PCC, PCC-R, and occurrence of phonological processes) and the aerodynamic (amplitude of the oral airflow and f0), eletroglottographic (open quotient) and acoustic (classification of voicing) measures were evaluated.

RESULTS

Numerically, children with speech sound disorders presented higher relative oral airflow amplitude, lower relative f0, and open quotient indicative of less efficient voicing production compared with those of children with typical development. The weak voicing values ​​showed that 66.1% of the children with speech sound disorders presented weaker voicing of the fricative sound /ʒ/ compared with that of the posterior vowel sound, and between-groups comparison demonstrated that these children presented greater difficulty in voicing. The acoustic analysis of speech used to classify the weak/strong voicing showed variations, especially regarding the classification partially devoiced.

CONCLUSION

Results suggest that the strategies for voicing production and voicing maintenance of the fricative sound /ʒ/ are still variable in children aged 5 years to 7 years and 11 months; however, children with speech sound disorders seem to have more difficulties in using them effectively. In addition, the study shows the importance of applying complementary tests to obtain a more detailed diagnosis.

Japanese macaque phonatory physiology

Although the call repertoire and its communicative function are relatively well explored in Japanese macaques (Macaca fuscata), little empirical data are available on the physics and the physiology of this species' vocal production mechanism. Here, a 6 year old female Japanese macaque was trained to phonate under an operant conditioning paradigm. The resulting 'coo' calls and spontaneously uttered 'growl' and 'chirp' calls were recorded with sound pressure level (SPL) calibrated microphones and electroglottography (EGG), a non-invasive method for assessing the dynamics of phonation. A total of 448 calls were recorded, complemented by ex vivo recordings on an excised Japanese macaque larynx. In this novel multidimensional investigative paradigm, in vivo and ex vivo data were matched via comparable EGG waveforms. Subsequent analysis suggests that the vocal range (range of fundamental frequency and SPL) of the macaque was comparable to that of a 7-10 year old human, with the exception of low intensity chirps, the production of which may be facilitated by the species' vocal membranes. In coo calls, redundant control of fundamental frequency in relation to SPL was also comparable to that in humans. EGG data revealed that growls, coos and chirps were produced by distinct laryngeal vibratory mechanisms. EGG further suggested changes in the degree of vocal fold adduction in vivo, resulting in spectral variation within the emitted coo calls, ranging from 'breathy' (including aerodynamic noise components) to 'non-breathy'. This is again analogous to humans, corroborating the notion that phonation in humans and non-human primates is based on universal physical and physiological principles.

[Impact of functional mass lesions in professional female singers : Biomechanics of vocal fold oscillation in the register transition regions]

BACKGROUND

The influence of functional mass lesions on vocal fold oscillation patterns in vocally challenging tasks is not yet understood in detail.

MATERIALS UND METHODS

Glissandi on the vowel [a:] from 220 to 440 Hz and 440 to 880 Hz were analyzed in three groups of four professional female singers: without a mass lesion or dysphony (group A), with a functional mass lesion (swellings without a great impact on oscillation patterns during stroboscopy; group B), and with organic dysphony (group C). High-speed digital imaging (HSDI; 20,000 fps), and acoustic and electroglottographic (EGG) signals were used for analysis. Based on the EGG sample entropy, time windows for analysis of register transition phenomena were constructed. The voice signals (glottal area waveform, GAW; acoustic and EGG signals) were perceptually rated in terms of the noticeability of registration events.

RESULTS

The absolute sample entropy revealed maxima in fundamental frequency regions where register transitions typically occur. Groups A and B could be distinguished neither by perceptual rating nor based on sample entropy values. In comparison to the other two groups, the absolute sample entropy values of group C were greater in the lower glissando. However, the larger vocal fold oscillatory irregularities were observable for the upper glissando in this group.

CONCLUSION

Functional mass lesions do not influence biomechanics adversely in vocally challenging tasks such as register transitions. The use of sample entropy as a criterion for detection of register transitions is promising, but needs further validation.

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.

Acoustic allometry revisited: morphological determinants of fundamental frequency in primate vocal production

A fundamental issue in the evolution of communication is the degree to which signals convey accurate ("honest") information about the signaler. In bioacoustics, the assumption that fundamental frequency (f o) should correlate with the body size of the caller is widespread, but this belief has been challenged by various studies, possibly because larynx size and body size can vary independently. In the present comparative study, we conducted excised larynx experiments to investigate this hypothesis rigorously and explore the determinants of f o. Using specimens from eleven primate species, we carried out an inter-specific investigation, examining correlations between the minimum f o produced by the sound source, body size and vocal fold length (VFL). We found that, across species, VFL predicted minimum f o much better than body size, clearly demonstrating the potential for decoupling between larynx size and body size in primates. These findings shed new light on the diversity of primate vocalizations and vocal morphology, highlighting the importance of vocal physiology in understanding the evolution of mammal vocal communication.

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.

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.

Analysis of vibratory states in phonation using spectral features of the electroglottographic signal

The vocal folds can oscillate in several different ways, manifest to practitioners and clinicians as "registers" or "mechanisms," of which the two most often considered are modal voice and falsetto voice. Here these will be taken as instances of different "vibratory states," i.e., distinct quasi-stationary patterns of vibration of the vocal folds. State transitions are common in biomechanical nonlinear oscillators, and they are often abrupt and impossible to predict exactly. Therefore, vibratory states are a source of confounding variation, for instance when acquiring a voice range profile (VRP). In the quest for a state-based, non-invasive VRP, a semi-automatic method based on the short-term spectrum of the electroglottographic (EGG) signal was developed. The method identifies rapid vibratory state transitions, such as the modal-falsetto switch, and clusters the EGG data based on their similarities in the relative levels and phases of the lower frequency components. Productions of known modal and falsetto voice were accurately clustered by a Gaussian mixture model. When mapped into the VRP, this EGG-based clustering revealed connected regions of different vibratory sub-regimes in both modal and falsetto.