Electroglottography

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.

Acoustic and Physiological Voice Assessment And Maximum Phonation Time In Patients With Different Types Of Dysarthria

OBJECTIVE

To compare the maximum phonation time of /a/, acoustic glottal source parameters, and physiological measures in patients with dysarthria.

METHOD

Thirteen patients were classified according to dysarthria type and divided into functional profiles (hypofunctional, hyperfunctional, and mixed). Assessments of maximum phonation time of /a/, glottal source parameters, electroglottography, and nasometry were performed. Results were compared between groups using ANOVA and Tukey posthoc tests.

RESULTS

The highest fundamental frequency differed significantly between groups, with the hyperfunctional profile showing higher values than the other participant groups. Reductions in the maximum phonation time of /a/ and alterations in acoustic glottal source parameters and electroglottography measures were observed in all groups, with no significant differences between them. The remaining measures did not differ between groups.

CONCLUSION

The maximum phonation times for /a/ were reduced in all participant groups, suggesting air escape during phonation. The presence of alterations in several glottal source parameters in all participant groups is indicative of noise, tremor, and vocal instability. Lastly, the high fundamental frequency in patients with a hyperfunctional profile reinforces the presence of vocal instability. These findings suggest that, although the characteristics observed in the assessments were consistent with expectations of patients with dysarthria, it is difficult to perform a differential diagnosis of this condition based on acoustic and physiological parameters alone.

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.

An investigation of interference between electromagnetic articulography and electroglottography

The present study tested whether there is cross-interference between electromagnetic articulography (EMA) and electroglottography (EGG) during the acquisition of kinematic speech data. In experiments 1A and 1B, EMA sensors were calibrated with and without EGG electrodes present in the EMA field. In experiment 2, EMA was used to record lip, tongue, and jaw movements for one male speaker and one female speaker, with and without simultaneous EGG recording. Collectively, the results provide no evidence of signal artifacts in either direction, suggesting that EMA and EGG technology can be combined to reliably assess laryngeal and supralaryngeal motor coordination in speech.

Quantitative and Qualitative Electroglottographic Wave Shape Differences in Children and Adults Using Voice Map-Based Analysis

Purpose The purpose of this study is to identify the extent to which various measurements of contacting parameters differ between children and adults during habitual range and overlap vocal frequency/intensity, using voice map-based assessment of noninvasive electroglottography (EGG). Method EGG voice maps were analyzed from 26 adults (22-45 years) and 22 children (4-8 years) during connected speech and vowel /a/ over the habitual range and the overlap vocal frequency/intensity from the voice range profile task on the vowel /a/. Mean and standard deviations of contact quotient by integration, normalized contacting speed, quotient of speed by integration, and cycle-rate sample entropy were obtained. Group differences were evaluated using the linear mixed model analysis for the habitual range connected speech and the vowel, whereas analysis of covariance was conducted for the overlap vocal frequency/intensity from the voice range profile task. Presence of a "knee" on the EGG wave shape was determined by visual inspection of the presence of convexity along the decontacting slope of the EGG pulse and the presence of the second derivative zero-crossing. Results The contact quotient by integration, normalized contacting speed, quotient of speed by integration, and cycle-rate sample entropy were significantly different in children compared to (a) adult males for habitual range and (b) adult males and adult females for the overlap vocal frequency/intensity. None of the children had a "knee" on the decontacting slope of the EGG slope. Conclusion EGG parameters of contact quotient by integration, normalized contacting speed, quotient of speed by integration, cycle-rate sample entropy, and absence of a "knee" on the decontacting slope characterize the wave shape differences between children and adults, whereas the normalized contacting speed, quotient of speed by integration, cycle-rate sample entropy, and presence of a "knee" on the downward pulse slope characterize the wave shape differences between adult males and adult females. Supplemental Material https://doi.org/10.23641/asha.15057345.

Nebulized Saline Solution: A Multidimensional Voice Analysis

PURPOSE

To verify the effect of nebulization on the voice of dysphonic and non-dysphonic individuals on acoustic, perceptual-auditory, aerodynamic, electroglottographic, laryngeal parameters and on the self-perception of vocal discomfort.

MATERIALS AND METHODS

All the research subjects were submitted to vocal evaluation, laryngeal and voice self-perception. Then, the participants remained in vocal rest for a period of 10 minutes and the analysis mentioned above were again performed. After this first stage, the participants were submitted to the nebulization for a period of 10 minutes and the all analysis above were again performed. Descriptive analysis of the variables was carried. In the comparison of the pre- and post-nebulization groups, the Paired T-Student Test was used for variables with non-dysphonic distribution and the Wilcoxon Test for variables with asymmetric distribution. When categorical variables were evaluated (perceptual-auditory evaluation and laryngeal assessment), the Pearson's Chi-square test was used. In all analysis, a significance level of 5% was considered. The intra-rater agreement in the auditory-perceptual and perceptual-visual assessment was assessed using the AC1 statistic, using the R program. For this purpose, 20% of the voice samples and laryngeal images were replicated blindly and interpreted by the evaluators at the time evaluations.

RESULTS

The results of this research show that non-dysphonic individuals have more positive vocal and laryngeal effects after nebulization than dysphonic ones. It is also observed that the EGG measurement was the most sensitive to the effect of nebulization, with an increase in the Closed quotient (CQ) in all groups evaluated. Regarding acoustic measurements, it is noted that the effect of nebulization in men is more evident than in women. After nebulization, there was an increase in fundamental frequency in the group of non-dysphonic women and dysphonic and non-dysphonic men. A decrease in the amplitude perturbation quotient values is observed in all groups, besides a reduction in the pitch perturbation quotient values after nebulization in non-dysphonic men groups. There was improves aerodynamic efficiency in groups of dysphonic and non-dysphonic men and in the self-perception of vocal discomfort in all groups studied after the hydration procedure. The results of this study demonstrate a significant improvement in the mucosal wave after nebulization in the groups of women and men who are not dysphonic.

CONCLUSION

The nebulization procedure with saline solution improves acoustic measurements, the electroglottographic closed quotient and vocal self-perception of dysphonic and non-dysphonic women and men. Nebulization increases the mucosal wave of the vocal folds in non-dysphonic women and men and improves the aerodynamic efficiency of men.

Female Voice-Related Sexual Attractiveness to Males: Does it Vary With Different Degrees of Conception Likelihood?

Previous investigations have found that female voice-related attractiveness to males increases when both conception likelihood (CL) and voice fundamental frequency (f_o) are elevated. To test this hypothesis, we conducted a perceptual experiment where 78 heterosexual males rated sexual attractiveness of 9 female voice samples, recorded at menstrual, follicular and luteal phases of the menstrual cycle under two double-blinded randomly allocated conditions: a natural menstrual cycle (placebo condition) and when using an oral contraceptive pill (OCP condition). The voice samples yielded a total of 54 stimuli that were visually sorted and rated using Visor software. Concentrations of estrogens, progesterone and testosterone were analyzed, and measurements of speaking fundamental frequency (sf_o) and its standard deviation (sf_oSD), f_o derivative (df_o) and f_o slope were made. A multilevel ordinal logistic regression model nested in listeners and in females, and adjusted by phase and condition, was carried out to assess the association between ratings and: (1) phases and conditions; (2) sex steroid hormonal concentrations; and (3) voice parameters. A high probability of obtaining high ratings of voice sexual attractiveness was found for: (1) menstrual phase of placebo use and follicular phase of OCP use; (2) for low estradiol to progesterone ratio and testosterone concentrations; and (3) for low df_o. The latter showed a moderate statistical association with ratings of high attractiveness, as compared with the small association found for the remaining variables. It seems that the voice is a weak cue for female CL. Female sexual attraction to males may be a consequence of what females do in order to regulate their extended sexuality across the menstrual cycle rather than of estrus cues, the use of paralinguistic speech patterns being an example.

Subglottal pressure oscillations in anechoic and resonant conditions and their influence on excised larynx phonations

Excised larynges serve as natural models for studying behavior of the voice source. Acoustic resonances inside the air-supplying tubes below the larynx (i.e., subglottal space), however, interact with the vibratory behavior of the larynges and obscure their inherent vibration properties. Here, we explore a newly designed anechoic subglottal space which allows removing its acoustic resonances. We performed excised larynx experiments using both anechoic and resonant subglottal spaces in order to analyze and compare, for the very first time, the corresponding subglottal pressures, electroglottographic and radiated acoustic waveforms. In contrast to the resonant conditions, the anechoic subglottal pressure waveforms showed negligible oscillations during the vocal fold contact phase, as expected. When inverted, these waveforms closely matched the inverse filtered radiated sound waveforms. Subglottal resonances modified also the radiated sound pressures (Level 1 interactions). Furthermore, they changed the fundamental frequency (fo) of the vocal fold oscillations and offset phonation threshold pressures (Level 2 interactions), even for subglottal resonance frequencies 4-10 times higher than fo. The obtained data offer the basis for better understanding the inherent vibratory properties of the vocal folds, for studying the impact of structure-acoustic interactions on voice, and for validation of computational models of voice production.

Consecuencias laringoscópicas, electroglotográficas, acústicas y sintomatológicas producidas por la sobrecarga vocal en mujeres con voces sanas y no entrenadas

La sobrecarga es una de las etapas del continuo de carga vocal. Actualmente, se considera que su investigación permite una mejor comprensión de la patología y sintomatología funcional de la voz. El objetivo de este trabajo fue analizar las consecuencias laringoscópicas, electroglotográficas, acústicas y sintomatológicas producidas por la sobrecarga vocal en mujeres con voces sanas y no entrenadas. Se examinó el comportamiento acústico, laringoscópico, electroglotográfico y sintomatológico de 30 mujeres que se sometieron a una tarea de sobrecarga vocal caracterizada por la lectura ininterrumpida de un texto durante 60 minutos, cuya intensidad fluctuó entre los 75 y 85 dB. A nivel laringoscópico, se observó mayor vascularización, aumento de la compresión supraglótica y cambios en la amplitud, simetría y onda mucosa. Acústicamente, se evidenció incremento significativo en la frecuencia fundamental e intensidad vocal. En la electroglotografía, el cociente de cierre y la fase abierta y cerrada disminuyeron significativamente, mientras que a nivel sintomatológico, la totalidad de la muestra expresó al menos un síntoma de fatiga vocal. En conclusión, los hallazgos observados son expresiones de la fatiga del mecanismo tiroaritenoideo y de la inflamación aguda de la cubierta cordal. 

Análise das medidas eletroglotográficas da voz: padrões de normalidade para cantores por meio do programa CSL da Kay Pentax®

RESUMO Objetivo: Analisar as medidas de frequência fundamental, jitter eletroglotográfico, quociente de contato e periodicidade das ondas eletroglotográficas da voz de cantores em registro modal. Método: Estudo observacional de corte transversal que selecionou indivíduos de escolas de canto da região central do município de Belo Horizonte-MG. A amostra foi não probabilística, por conveniência, composta por 60 indivíduos cantores com faixa etária entre 18 e 55 anos, sendo 30 homens e 30 mulheres. Para a coleta do registro eletroglotográfico, foi utilizado o programa CSL da Kay Pentax™, model 6103, módulo Electroglottography. Os participantes foram posicionados sentados e, após a higienização da pele do pescoço com álcool 70 %, dois eletrodos foram colocados nas alas da cartilagem tireóidea no nível das pregas vocais. Posteriormente, os participantes foram orientados a emitir a vogal /a/ sustentada de forma habitual. Foram analisadas as medidas de frequência fundamental (f0), quociente de contato (QC), jitter eletroglotográfico e periodicidade da onda eletroglotográfica. Os dados foram analisados estatisticamente utilizando o Minitab 17. Resultados: Os parâmetros analisados foram estatisticamente significantes. A frequência fundamental (f0) foi maior nas mulheres (226,91 Hz) quando comparada com a dos homens (166,54 Hz). As medidas de quociente de contato e de periodicidade também foram maiores nas mulheres (40,46 % e 15,51 %, respectivamente) se comparadas às dos homens (27,45 % e 7,82, respectivamente). O parâmetro de jitter foi maior nos homens, quando comparado ao das mulheres. Conclusão: Os valores de frequência fundamental (f0), quociente de contato (QC) e periodicidade da onda foram maiores nas mulheres. O valor de jitter foi maior nos homens.

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.

Normalized time-domain parameters for electroglottographic waveforms

The electroglottographic waveform is of interest for characterizing phonation non-invasively. Existing parameterizations tend to give disparate results because they rely on somewhat arbitrary thresholds and/or contacting events. It is shown that neither are needed for formulating a normalized contact quotient and a normalized peak derivative. A heuristic combination of the two resolves also the ambiguity of a moderate contact quotient, with regard to vocal fold contacting being firm versus weak or absent. As preliminaries, schemes for electroglottography signal preconditioning and time-domain period detection are described that improve somewhat on similar methods. The algorithms are simple and compute quickly.

Pitch-Synchronous Analysis of Human Voice

OBJECTIVE

Based on simultaneous voice and electroglottograph (EGG) signals, to gain a better understanding of human voice production process, to make pitch-synchronous segmentation of voice signals, and to make visual representations of pitch marks and timbre spectra with high resolution.

METHODS/DESIGN

The traditional spectrogram segments the voice signals with a process window of fixed size and fixed shift, then performs fast Fourier transformation after multiplied with a window function, typically a Hamming window. Then display power spectrum in both frequency and time. Pitch information and timbre information are mixed. The new design segments the signals into pitch periods, either using the derivatives of the EGG signals or based on the voice signals, then performs Fourier analysis to the segment of signals in each pitch period without using a window function. The pitch information and the timbre information are cleanly separated. The graphical representations of both pitch marks and timbre spectra exhibit high resolution and high accuracy.

RESULTS

Detailed analysis of simultaneously acquired voice and EGG signals provides a more precise understanding of human-voice production process. The transient theory of voice production, proposed by Leonhard Euler in early 18th century, is substantiated with modern data. Based on the transient theory of voice production, a pitch-synchronous spectrogram software is developed, which makes a visual representation of pitch marks and timbre spectra. In addition, the timbre spectrum and the power evolution pattern in each pitch period can be displayed individually.

CONCLUSIONS

Simultaneously acquired voice and EGG signals indicates that each glottal closing triggers a decaying elementary wave in the vocal tract. A superposition of those elementary waves constitutes voice. Based on that concept and using EGG data, a pitch-synchronous voice signal processing method is developed. The voice signal is first segmented into pitch periods, then the two ends are equalized. Fourier analysis is applied to obtain the timbre spectrum of each pitch period. High resolution display of timbre spectrum is generated. The power evolution pattern in each pitch period is also displayed.

Effects of the Lung Volume on the Electroglottographic Waveform in Trained Female Singers

OBJECTIVES

To determine if in singing there is an effect of lung volume on the electroglottographic waveform, and if so, how it varies over the voice range.

STUDY DESIGN

Eight trained female singers sang the tune "Frère Jacques" in 18 conditions: three phonetic contexts, three dynamic levels, and high or low lung volume. Conditions were randomized and replicated.

METHODS

The audio and EGG signals were recorded in synchrony with signals tracking respiration and vertical larynx position. The first 10 Fourier descriptors of every EGG cycle were computed. These spectral data were clustered statistically, and the clusters were mapped by color into a voice range profile display, thus visualizing the EGG waveform changes under the influence of f_o and SPL. The rank correlations and effect sizes of the relationships between relative lung volume and several adduction-related EGG wave shape metrics were similarly rendered on a color scale, in voice range profile-style 'voice maps.'

RESULTS

In most subjects, EGG waveforms varied considerably over the voice range. Within subjects, reproducibility was high, not only across the replications, but also across the phonetic contexts. The EGG waveforms were quite individual, as was the nature of the EGG shape variation across the range. EGG metrics were significantly correlated to changes in lung volume, in parts of the range of the song, and in most subjects. However, the effect sizes of the relative lung volume were generally much smaller than the effects of f_o and SPL, and the relationships always varied, even changing polarity from one part of the range to another.

CONCLUSIONS

Most subjects exhibited small, reproducible effects of the relative lung volume on the EGG waveform. Some hypothesized influences of tracheal pull were seen, mostly at the lowest SPLs. The effects were however highly variable, both across the moderately wide f_o-SPL range and across subjects. Different singers may be applying different techniques and compensatory behaviors with changing lung volume. The outcomes emphasize the importance of making observations over a substantial part of the voice range, and not only of phonations sustained at a few fundamental frequencies and sound levels.

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.

Measurement of the Maximum Frequency of Electroglottographic Fluctuations in the Expiration Phase of Volitional Cough as a Functional Test for Cough Efficiency

The hypotheses of the present study were that the maximum frequency of fluctuation of electroglottographic (EGG) signals in the expiration phase of volitional cough (VC) reflects the cough efficiency and that this EGG parameter is affected by impaired laryngeal closure, expiratory effort strength, and gender. For 20 normal healthy adults and 20 patients diagnosed with unilateral vocal fold paralysis (UVFP), each participant was fitted with EGG electrodes on the neck, had a transnasal laryngo-fiberscope inserted, and was asked to perform weak/strong VC tasks while EGG signals and a high-speed digital image of the larynx were recorded. The maximum frequency was calculated in the EGG fluctuation region coinciding with vigorous vocal fold vibration in the laryngeal HSDIs. In addition, each participant underwent spirometry for measurement of three aerodynamic parameters, including peak expiratory air flow (PEAF), during weak/strong VC tasks. Significant differences were found for both maximum EGG frequency and PEAF between the healthy and UVFP groups and between the weak and strong VC tasks. Among the three cough aerodynamic parameters, PEAF showed the highest positive correlation with the maximum EGG frequency. The correlation coefficients between the maximum EGG frequency and PEAF recorded simultaneously were 0.574 for the whole group, and 0.782/0.717/0.823/0.688 for the male/female/male-healthy/male-UVFP subgroups, respectively. Consequently, the maximum EGG frequency measured in the expiration phase of VC was shown to reflect the velocity of expiratory airflow to some extent and was suggested to be affected by vocal fold physical properties, glottal closure condition, and the expiratory function.

Phonatory Strategies of Male Vocalists in Singing Diatonic Scales With Various Dynamic Shapings

This work aimed to investigate glottal adduction in the case of the singing of diatonic D major ascending scales with different dynamic shapings on vowel [a:] by 10 classically trained male singers. The parameters obtained by inverse filtering-closed quotient (CQ), normalized amplitude quotient (NAQ), and the level difference between the first two partials of the glottal flow waveform spectrum (H1-H2)-all indicated statistically significant systematic changes when singers sang (1) with habitual dynamics without intentional dynamic changes; (2) with sempre crescendo from piano to forte; and (3) with sempre diminuendo from forte to piano. Adduction on average was lower if the tone with the same pitch was sung piano compared with when it was sung forte. The piano tones with the limit of one and the same dynamic task were sung with lower adduction on average compared with one octave higher or lower tones sung forte, although here the agreement between different parameters was poorer and the individual variability was greater. There was only a moderate negative correlation between CQ and NAQ (r = -0.41) but a strong negative correlation between CQ and H1-H2 (r = -0.8). CQ showed a moderate positive correlation with sound level but no significant correlation with pitch. NAQ showed a strong and significant positive correlation with pitch but not with sound level (except when it was calculated only at constant pitch). Some of the most experienced singers used quite high glottal adduction levels, questioning the concept of whether flow phonation is always the favorite classical style.

Analysis of voice quality in patients with late-onset Pompe disease

Background

Pompe disease is a progressive metabolic myopathy. Disease progression is characterized, among other features, by progressive dysfunction of the voice apparatus. The aim of this study was to employ electroglottographic, acoustic and nasalance measurement methods on patients with late-onset Pompe disease in order to provide detailed information on the effect of the disease on voice quality. Voice quality is the key factor for estimating the effectiveness of ERT in late-onset Pompe disease. The study compared clinical phoniatric examination with electroglottographic, acoustic and nasalance measurement methods. The consistency of the aforementioned analyses was assessed.

Methods

The study examined 19 patients with late-onset Pompe disease (including 9 with the juvenile form of the disease). Of these, a total of 17 patients underwent otolaryngological examination with detailed phoniatric evaluation of their articulatory organs. Electroglottographic recordings and nasalance measurements (using the nasalance Separator Handle) were obtained from all patients. MATLAB (COVAREP toolkit) was used to analyse voice recording data.

Results

Dysphonia observed in patients with late-onset Pompe disease is mainly caused by dysfunction of vocal fold closure and weakness of vocal muscle. However, substantial speech nasality is caused by insufficient closure of the soft palate. Electroglottographic signal analysis, acoustic and nasalance testing methods indicated that more significant changes in the function of the voice apparatus presented in the juvenile form than in the adult form of late-onset Pompe disease.

Conclusions

It was found that speech nasality and electroglottographic tests are more repeatable, comparable and versatile than phoniatric examination, allowing for earlier detection of voice pathology in late-onset Pompe disease. These sensitive and non-invasive acoustic and electroglottographic methods allow for the tracking of changes in voice as patients undergo treatment or as the disease progresses.

Universal mechanisms of sound production and control in birds and mammals

As animals vocalize, their vocal organ transforms motor commands into vocalizations for social communication. In birds, the physical mechanisms by which vocalizations are produced and controlled remain unresolved because of the extreme difficulty in obtaining in vivo measurements. Here, we introduce an ex vivo preparation of the avian vocal organ that allows simultaneous high-speed imaging, muscle stimulation and kinematic and acoustic analyses to reveal the mechanisms of vocal production in birds across a wide range of taxa. Remarkably, we show that all species tested employ the myoelastic-aerodynamic (MEAD) mechanism, the same mechanism used to produce human speech. Furthermore, we show substantial redundancy in the control of key vocal parameters ex vivo, suggesting that in vivo vocalizations may also not be specified by unique motor commands. We propose that such motor redundancy can aid vocal learning and is common to MEAD sound production across birds and mammals, including humans.

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.

Does Cervical Muscular Contraction Affect the Measurement for Electroglottographic Perturbation Parameters?

OBJECTIVES

The purpose was to assess whether cervical muscular contraction during phonation influences the period and amplitude perturbation quotients (PPQ and APQ, respectively) of electroglottographic (EGG) signals, and whether high-pass filtering can attenuate these effects.

STUDY DESIGN

Prospective.

METHODS

We included 19 nondysphonic speakers and 21 patients with muscle tension dysphonia. During the recording of acoustic and EGG signals, each participant was instructed to naturally phonate sustained vowels /i:/ and /a:/ (NP tasks), and additionally, each nondysphonic participant was asked to phonate the same vowels in a nondysphonic voice quality while contracting the cervical muscles (muscular contracted phonation [MCP] tasks). To confirm the contraction, surface and needle electromyography (EMG) was performed. The EGG signals were high-pass filtered at different cutoff frequencies from 0 to 90 Hz and were subsequently analyzed for the PPQ and APQ.

RESULTS

Compared with the NP tasks, the MCP tasks enhanced the cervical EMG activities ranging from 0 to more than 1000 Hz, but conferred only low-frequency noise to the EGG signals under 50 Hz and increased the values for EGG-APQ, but not EGG-PPQ. These EGG-APQ values exhibited gradual decreases after high-pass filtering with an increase in the cutoff frequency ranging from 0 to 50 Hz in both groups, followed by plateaus during the MCP tasks in the nondysphonic group.

CONCLUSIONS

The present results demonstrate that cervical muscular contraction seriously affects the EGG-APQ values for unfiltered EGG signals independent of the EMG activities and that appropriate high-pass filtering over 50 Hz can attenuate these effects.

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.

The glottaltopogram: a method of analyzing high-speed images of the vocal folds

Laryngeal high-speed videoendoscopy is a state-of-the-art technique to examine physiological vibrational patterns of the vocal folds. With sampling rates of thousands of frames per second, high-speed videoendoscopy produces a large amount of data that is difficult to analyze subjectively. In order to visualize high-speed video in a straightforward and intuitive way, many methods have been proposed to condense the three-dimensional data into a few static images that preserve characteristics of the underlying vocal fold vibratory patterns. In this paper, we propose the "glottaltopogram," which is based on principal component analysis of changes over time in the brightness of each pixel in consecutive video images. This method reveals the overall synchronization of the vibrational patterns of the vocal folds over the entire laryngeal area. Experimental results showed that this method is effective in visualizing pathological and normal vocal fold vibratory patterns.

Quantitative measurement of vocal fold vibration in male radio performers and healthy controls using high-speed videoendoscopy

PURPOSE

Acoustic and perceptual studies show a number of differences between the voices of radio performers and controls. Despite this, the vocal fold kinematics underlying these differences are largely unknown. Using high-speed videoendoscopy, this study sought to determine whether the vocal vibration features of radio performers differed from those of non-performing controls.

METHOD

Using high-speed videoendoscopy, recordings of a mid-phonatory/i/ in 16 male radio performers (aged 25-52 years) and 16 age-matched controls (aged 25-52 years) were collected. Videos were extracted and analysed semi-automatically using High-Speed Video Program, obtaining measures of fundamental frequency (f0), open quotient and speed quotient. Post-hoc analyses of sound pressure level (SPL) were also performed (n = 19). Pearson's correlations were calculated between SPL and both speed and open quotients.

RESULTS

Male radio performers had a significantly higher speed quotient than their matched controls (t = 3.308, p = 0.005). No significant differences were found for f0 or open quotient. No significant correlation was found between either open or speed quotient with SPL.

DISCUSSION

A higher speed quotient in male radio performers suggests that their vocal fold vibration was characterised by a higher ratio of glottal opening to closing times than controls. This result may explain findings of better voice quality, higher equivalent sound level and greater spectral tilt seen in previous research. Open quotient was not significantly different between groups, indicating that the durations of complete vocal fold closure were not different between the radio performers and controls. Further validation of these results is required to determine the aetiology of the higher speed quotient result and its implications for voice training and clinical management in performers.

Complex vibratory patterns in an elephant larynx

Elephants' low-frequency vocalizations are produced by flow-induced self-sustaining oscillations of laryngeal tissue. To date, little is known in detail about the vibratory phenomena in the elephant larynx. Here, we provide a first descriptive report of the complex oscillatory features found in the excised larynx of a 25 year old female African elephant (Loxodonta africana), the largest animal sound generator ever studied experimentally. Sound production was documented with high-speed video, acoustic measurements, air flow and sound pressure level recordings. The anatomy of the larynx was studied with computed tomography (CT) and dissections. Elephant CT vocal anatomy data were further compared with the anatomy of an adult human male. We observed numerous unusual phenomena, not typically reported in human vocal fold vibrations. Phase delays along both the inferior-superior and anterior-posterior (A-P) dimension were commonly observed, as well as transverse travelling wave patterns along the A-P dimension, previously not documented in the literature. Acoustic energy was mainly created during the instant of glottal opening. The vestibular folds, when adducted, participated in tissue vibration, effectively increasing the generated sound pressure level by 12 dB. The complexity of the observed phenomena is partly attributed to the distinct laryngeal anatomy of the elephant larynx, which is not simply a large-scale version of its human counterpart. Travelling waves may be facilitated by low fundamental frequencies and increased vocal fold tension. A travelling wave model is proposed, to account for three types of phenomena: A-P travelling waves, 'conventional' standing wave patterns, and irregular vocal fold vibration.

Comparison of voice relative fundamental frequency estimates derived from an accelerometer signal and low-pass filtered and unprocessed microphone signals

The relative fundamental frequency (RFF) surrounding the production of a voiceless consonant has previously been estimated using unprocessed and low-pass filtered microphone signals, but it can also be estimated using a neck-placed accelerometer signal that is less affected by vocal tract formants. Determining the effects of signal type on RFF will allow for comparisons across studies and aid in establishing a standard protocol with minimal within-speaker variability. Here RFF was estimated in 12 speakers with healthy voices using unprocessed microphone, low-pass filtered microphone, and unprocessed accelerometer signals. Unprocessed microphone and accelerometer signals were recorded simultaneously using a microphone and neck-placed accelerometer. The unprocessed microphone signal was filtered at 350 Hz to construct the low-pass filtered microphone signal. Analyses of variance showed that signal type and the interaction of vocal cycle × signal type had significant effects on both RFF means and standard deviations, but with small effect sizes. The overall RFF trend was preserved regardless of signal type and the intra-speaker variability of RFF was similar among the signal types. Thus, RFF can be estimated using either a microphone or an accelerometer signal in individuals with healthy voices. Future work extending these findings to individuals with disordered voices is warranted.

Glottal opening and closing events investigated by electroglottography and super-high-speed video recordings

Previous research has suggested that the peaks in the first derivative (dEGG) of the electroglottographic (EGG) signal are good approximate indicators of the events of glottal opening and closing. These findings were based on high-speed video (HSV) recordings with frame rates 10 times lower than the sampling frequencies of the corresponding EGG data. The present study attempts to corroborate these previous findings, utilizing super-HSV recordings. The HSV and EGG recordings (sampled at 27 and 44 kHz, respectively) of an excised canine larynx phonation were synchronized by an external TTL signal to within 0.037 ms. Data were analyzed by means of glottovibrograms, digital kymograms, the glottal area waveform and the vocal fold contact length (VFCL), a new parameter representing the time-varying degree of ‘zippering’ closure along the anterior–posterior (A–P) glottal axis. The temporal offsets between glottal events (depicted in the HSV recordings) and dEGG peaks in the opening and closing phase of glottal vibration ranged from 0.02 to 0.61 ms, amounting to 0.24–10.88% of the respective glottal cycle durations. All dEGG double peaks coincided with vibratory A–P phase differences. In two out of the three analyzed video sequences, peaks in the first derivative of the VFCL coincided with dEGG peaks, again co-occurring with A–P phase differences. The findings suggest that dEGG peaks do not always coincide with the events of glottal closure and initial opening. Vocal fold contacting and de-contacting do not occur at infinitesimally small instants of time, but extend over a certain interval, particularly under the influence of A–P phase differences.

Visualization of system dynamics using phasegrams

A new tool for visualization and analysis of system dynamics is introduced: the phasegram. Its application is illustrated with both classical nonlinear systems (logistic map and Lorenz system) and with biological voice signals. Phasegrams combine the advantages of sliding-window analysis (such as the spectrogram) with well-established visualization techniques from the domain of nonlinear dynamics. In a phasegram, time is mapped onto the x-axis, and various vibratory regimes, such as periodic oscillation, subharmonics or chaos, are identified within the generated graph by the number and stability of horizontal lines. A phasegram can be interpreted as a bifurcation diagram in time. In contrast to other analysis techniques, it can be automatically constructed from time-series data alone: no additional system parameter needs to be known. Phasegrams show great potential for signal classification and can act as the quantitative basis for further analysis of oscillating systems in many scientific fields, such as physics (particularly acoustics), biology or medicine.

Phonovibrographic wavegrams: visualizing vocal fold kinematics

Recently, endoscopic high-speed laryngoscopy has been established for commercial use as a state-of-the-art technique to examine vocal fold kinematics. Since modern cameras provide sampling rates of several thousand frames per second, a high volume of data has to be considered for visual and objective analysis. A method for visualizing endoscopic high speed videos in three-dimensional cycle-based graphs combining and extending the approaches of phonovibrograms and electroglottographic wavegrams is presented. To build a phonovibrographic wavegram, individual cycles of a phonovibrogram are segmented, normalized in cycle duration, and concatenated over time. For analyzing purposes, the emerging three-dimensional scalar field is visualized with different rendering techniques providing information of different aspects of vocal fold kinematics. The phonovibrographic wavegram incorporates information about the glottal closure type, size, and location of the amplitudes, symmetry, periodicity, and phase information. The potential of the approach to visualize the characteristics of vocal fold vibration in a compact and intuitive way is demonstrated within two healthy and three pathologic subjects. The phonovibrographic wavegram allows a comprehensive analysis of vocal fold kinematics and reveals information that remains hidden with other visualization techniques.

How low can you go? Physical production mechanism of elephant infrasonic vocalizations

Elephants can communicate using sounds below the range of human hearing ("infrasounds" below 20 hertz). It is commonly speculated that these vocalizations are produced in the larynx, either by neurally controlled muscle twitching (as in cat purring) or by flow-induced self-sustained vibrations of the vocal folds (as in human speech and song). We used direct high-speed video observations of an excised elephant larynx to demonstrate flow-induced self-sustained vocal fold vibration in the absence of any neural signals, thus excluding the need for any "purring" mechanism. The observed physical principles of voice production apply to a wide variety of mammals, extending across a remarkably large range of fundamental frequencies and body sizes, spanning more than five orders of magnitude.