Electroglottographic Signals Research Articles

Characterization of laryngealization as irregular vocal fold vibration and interaction with prosodic prominence

This paper introduces an original variant of recurrence analysis to quantify the degree of regularity of vocal fold vibration as captured by electroglottography during phonation. The proposed technique is applied to the analysis of laryngealized phonation as this phonation type typically shows irregular vibration cycles. The reliability of this approach is validated with synthetic vocal fold vibration signals, demonstrating that it permits measuring the regularity of vocal fold vibration, unaffected by changes in fundamental frequency. The method is also applied to real electroglottographic signals recorded at the onset of vowel-initial nonsense words produced in a speeded repetition task by five female German speakers. Results show that the degree of laryngealization during the production of word-initial vowels is modulated by the presence of stress (with stressed vowels being less laryngealized). Due to its robustness to changes of F0, the proposed technique proves to be a suitable tool for studying vocal fold regularity in concatenated speech. Its applications are not limited to the study of glottalization, since the degree of regularity of vocal fold vibration has paralinguistic functions and is a clinically relevant measure of voice pathologies.

Improving reliability of measurement algorithms in differentiated electroglottograph and audio signals

The purpose of this work was to develop an optimized algorithm for determining the closed quotient (CQ) measurements of the vocal folds of female singers. This study extends previous results which showed that the measurement algorithm for differentiated electroglottograph (dEGG) signals and differentiated audio (dAUDIO) signals gave moderately reliable results with a correlation coefficient of r = 0.79. Additional performance studies indicate that the reliability may be improved by combining the differential signals and modifying the measurement algorithm to reduce the amount of signal overlap. Preliminary results using the modified measurement algorithm yield a significant increase in the correlation coefficient (r = 0.83). This works contributes to the development of a computational framework for determining accurate and reliable measurements for characterizing register shifts through an octave in female singers using electroglottography.

Relationship Between the Electroglottographic Signal and Vocal Fold Contact Area

Electroglottography (EGG) is a widely used noninvasive method that purports to measure changes in relative vocal fold contact area (VFCA) during phonation. Despite its broad application, the putative direct relation between the EGG waveform and VFCA has to date only been formally tested in a single study, suggesting an approximately linear relationship. However, in that study, flow-induced vocal fold (VF) vibration was not investigated. A rigorous empirical evaluation of EGG as a measure of VFCA under proper physiological conditions is therefore still needed. Three red deer larynges were phonated in an excised hemilarynx preparation using a conducting glass plate. The time-varying contact between the VF and the glass plate was assessed by high-speed video recordings at 6000 fps, synchronized to the EGG signal. The average differences between the normalized [0, 1] VFCA and EGG waveforms for the three larynges were 0.180 (±0.156), 0.075 (±0.115), and 0.168 (±0.184) in the contacting phase and 0.159 (±0.112), -0.003 (±0.029), and 0.004 (±0.032) in the decontacting phase. Overall, there was a better agreement between VFCA and the EGG waveform in the decontacting phase than in the contacting phase. Disagreements may be caused by nonuniform tissue conductance properties, electrode placement, and electroglottograph hardware circuitry. Pending further research, the EGG waveform may be a reasonable first approximation to change in medial contact area between the VFs during phonation. However, any quantitative and statistical data derived from EGG should be interpreted cautiously, allowing for potential deviations from true VFCA.

Vocal Attack Time of Different Pitch Levels and Vowels in Mandarin

The purpose of this study was to investigate how vocal attack time (VAT) varies when young adults articulate the three vertex vowels in Mandarin Chinese at five linguistically unconstrained pitch levels. Sound pressure and electroglottographic signals were recorded simultaneously from 53 male and 53 female subjects saying sustained /A/, /i/, and /u/ at five equally spaced pitch heights, each being higher than the preceding one. Then analyses of means, variance, and correlation were performed to explore the relationships of VAT/pitch levels and VAT/vowels. Findings were As mean STs (semitone) increase linearly from levels 1 to 5, mean VATs decrease nonlinearly in a big group of subjects but increase nonlinearly in a small group of them. Based on the body-cover model of F0 control, data here lead to the guess that different people incline to use different strategies in increasing pitch height. When males, females, and males plus females are considered as a whole, average STs and VATs tend to be positively correlated among the three vertex vowels.

Lab Work for the Non-PhD? Absolutely!

Lab Work for the Non-PhD? Absolutely!

Influence of F0 and Sequence Length of Audio and Electroglottographic Signals on Perturbation Measures for Voice Assessment

Within the functional assessment of voice disorders, an objective analysis of measured parameters from audio, electroglottographic (EGG), or visual signals is desired. In a typical clinical situation, reliable objective analysis is not always possible due to missing standardization and unknown stability of the clinical parameters. The aim of this study was to investigate the robustness/stability of measured clinical parameters of the audio and EGG signals in a typical clinical setting to ensure a reliable objective analysis. In particular, the influence of F0 and of the sequence length on several definitions of jitter and shimmer will be analyzed. Seventy-four young healthy women produced a sustained vowel /a/ and an upward triad with abrupt changeovers. Different sequence lengths (100, 150, 500, and 1000ms) of sustained phonation and triads (100 and 150ms) were extracted from the audio and EGG signals. In total, six variations of jitter and four variations of shimmer parameters were analyzed. Jitter%, Jitter11p, and JitterPPQ of the audio signal as well as Jittermean, Shimmer, and Shimmer11p of the EGG signal are unaffected by both sequence length and F0. Influence of F0 and sequence length on several perturbation measures of the audio and EGG signals was identified. For an objective clinical voice assessment, unaffected definitions of jitter and shimmer should be preferred and applied to enable comparability between different recordings, examinations, and studies.

Instantaneous voiced/non-voiced detection in speech signals based on variational mode decomposition

In this paper, a variational mode decomposition (VMD) based method has been proposed for the instantaneous detection of voiced/non-voiced (V/NV) regions in the speech signals. In the proposed method, the VMD is applied in iterative way with specific input parameters. Firstly, the VMD decomposes the speech signal into two components, then, the VMD is applied successively on one of these two components based on suitably defined convergence criteria. It has been shown that the VMD applied in iterative way behaves as a low-pass filter and after convergence it provides separation of the fundamental frequency (F0) component from the speech signal. The envelope of the F0 component of the speech signal has been obtained using an analytical model based on single degree of freedom (SDOF). Automatic threshold has been computed from the obtained envelope in order to detect the V/NV regions in speech signals. The proposed method has been studied on speech signals and the corresponding electroglottograph (EGG) signals from the CMU-Arctic database in different noise conditions obtained from the NOISEX-92 database. Experimental results at various signal to noise ratios (SNRs) are included in order to show the effectiveness of the proposed method compared to the other existing methods for V/NV detection in speech signals.

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

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. Prospective. 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 90Hz and were subsequently analyzed for the PPQ and APQ. Compared with the NP tasks, the MCP tasks enhanced the cervical EMG activities ranging from 0 to more than 1000Hz, but conferred only low-frequency noise to the EGG signals under 50Hz 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 50Hz in both groups, followed by plateaus during the MCP tasks in the nondysphonic group. 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 50Hz can attenuate these effects.

Differentiated electroglottograph and audio signal measurements of vocal fold closed quotient during a register change: Single note data

Recently, the use of the differentiated electroglottograph (dEGG) signal combined with a differentiated audio (dAudio) signal was reported as a means for more reliable measurement of the closing quotient (CQ) from the EGG signal in combination with a time synchronized audio signal. The purpose of this study is to combine CQ data with resonance data from the vocal tract during a register shift. Files recorded from group of 15 trained females provided the data. The singers were directed to shift between chest and mixed registers while sustaining a note that could be sung comfortably in both registers. An EGG and an audio signal were recorded. These signals were time aligned, and the EGG, dEGG, and dAudio were displayed. These three signals were used to determine the CQ and peak resonant amplitude before and after the register shift. Preliminary results indicate that the singers maintained a similar CQ measurement across the register shift. In addition, the preliminary data indicate that the singers changed the dominant harmonic in the sung note when they changed registers. That is, they maintained the same fundamental frequency but altered the resonance of the tone in the vocal tract.

An Examination of the Relationship Between Electroglottographic Contact Quotient, Electroglottographic Decontacting Phase Profile, and Acoustical Spectral Moments

To date, only a few studies have examined the possible relationship between electroglottographic (EGG) data and spectral characteristics of the voice. This study examined the possible association between EGG signal data (contact quotient [CQ] and decontacting phase profile) and spectral moments of the acoustic signal (spectral mean, spectral standard deviation (SD), spectral skewness, and spectral kurtosis). Furthermore, the possible effects of gender on these measurements were analyzed. Sustained vowel /ɑ/ productions were obtained from 48 normophonic individuals (24 adult males and 24 adult females). The central 1-second portions of the acoustic vowel samples were analyzed for spectral moments, and the EGG signal was analyzed for CQ (CQEGG), fundamental frequency (F0), and decontacting phase profile. Across all subjects, the spectral characteristics of the voice (in particular, spectral SD, skewness, and kurtosis) are significantly related to changes in the relative duration of vocal fold contact (as measured via CQEGG). In addition, significant effects of the profile of the EGG decontacting phase (ie, concave down/"knee" vs concave up/"no knee") on spectral SD were also observed, as well as a strong trend for decontacting phase profile to influence the spectral mean. Although the degree of vocal fold contact and differences in decontacting phase profile may have an influence on the spectral characteristics of the acoustic voice signal, the strength of correlations between CQEGG values and measures of spectral moments only accounted for approximately 13-16% of the variation in spectral distribution characteristics. These results stress the importance of the transformative role of the supraglottal vocal tract in producing an acoustic output that maintains some of the characteristics of the glottal source, but which modifies the source characteristics in ways not completely accounted for by single parameters such as CQEGG or EGG profile.

Effect of Voice Onset Type on Vocal Attack Time

Vocal attack time (VAT) is the time lag between the growth of sound pressure (SP) and electroglottographic (EGG) signals at vocal initiation. The characteristics of voice initiation are associated with issues of vocal hygiene, efficiency, and quality. Vocal onsets have commonly been qualitatively characterized into three types: hard, simultaneous, and breathy. This study examines the effect of voice onset type on VAT values in normal speakers. SP and EGG recordings were obtained for 55 female and 57 male subjects while producing multiple tokens of three tasks (sustained /ɑ/ and "always" as unaspirated onsets, and "hallways" as an aspirated onset). Results revealed a significant effect of onset type on VAT, with the mean VAT for the "hallways" (aspirated) task greater than the mean VAT for the sustained /ɑ/ and "always" (unaspirated) tasks. There was no significant VAT difference between the sustained /ɑ/ and "always" tasks. Findings confirm the sensitivity of the VAT measure to vocal onset type and suggest its potential application as an objective and quantitative clinical measure of the type of vocal onset.

Comparison of Tongue and Lip Trills with Phonation of the Sustained Vowel /<i>ε</i>/ Regarding the Periodicity of the Electroglottographic Waveform and the Amplitude of the Electroglottographic Signal

Aim: The aim is to compare the vocal fold vibration seen during lip and tongue trills with that seen during phonation of the sustained vowel /ε/, in terms of the periodicity of the EGG waveform and the amplitude of the EGG signal, in professional voice users. Study design: This was a quasi-experimental study. Methods: We used electroglottography (EGG) to compare the vocal fold vibration seen during tongue and lip trills with that seen during phonation of the sustained vowel /ε/, in terms of the EGG waveform periodicity and signal amplitude, in 10 classically trained, professional singers. The participants produced the sustained vowel /ε/ and performed tongue and lip trills at the same frequency and intensity. The periodicity of the waveform and the amplitude of the signal were visually analyzed by three blinded, experienced readers. To confirm the visual analysis results, we measured the jitter and shimmer of the signal and the frequency of variation in vocal fold vibration during the trill exercises. Results: The EGG waveform was classified as periodic for the sustained vowel phonation task and as quasi-periodic for the trill exercises, the vibration pattern repeating at approximately 24 Hz. Conclusion: The vibration of the vocal folds was modified according to the supraglottic movement in trills exercises.

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.

Study of the effects of vocal tract constriction on glottal vibration.

Characteristics of glottal vibration are affected by the obstruction to the flow of air through the vocal tract system. The obstruction to the airflow is determined by the nature, location, and extent of constriction in the vocal tract during production of voiced sounds. The effects of constriction on glottal vibration are examined for six different categories of speech sounds having varying degree of constriction. The effects are examined in terms of source and system features derived from the speech and electroglottograph signals. It is observed that a high degree of constriction causing obstruction to the flow of air results in large changes in these features, relative to the adjacent steady vowel regions, as in the case of apical trill and alveolar fricative sounds. These changes are insignificant when the obstruction to the airflow is less, as in the case of velar fricative and lateral approximant sounds. There are no changes in the excitation features when there is a free flow of air along the auxiliary tract, despite constriction in the vocal tract, as in the case of nasals. These studies show that effects of constriction can indeed be observed in the features of glottal vibration as well as vocal tract resonances.

Combining differentiated electroglottograph and differentiated audio signals to reliably measure vocal fold closed quotient

Over the past few decades researchers have explored the use of the electroglottograph (EGG) as a non-invasive method for representing vocal fold contact during vowel production and to measure the closed quotient (CQ) and open quotient (OQ) of the glottal cycle. The first derivative of the EGG signal (dEGG) can be used to indicate these moments (Childers & Krishnamurthy, 1985). However, there can be double positive peaks in the dEGG as well as a variety of negative peak patterns (Herbst et al., 2010). Obviously these variations will alter any measurements made from the signal. Recently, the use of the dEGG with dAudio signal was reported as a means for more reliable measurement of the CQ from the EGG signal in combination with a time synchronized audio signal. The purpose of this study is to demonstrate the reliability of the dEGG and dAudio for determining CQ across a variety of vocal conditions. Files recorded from group of 15 trained females singing an octave that included their primo passaggio provided the data. Preliminary results indicate high reliability of the CQ measurements in both the chest and middle registers of all of the singers.

Analysis of production characteristics of laughter

In this paper, the production characteristics of laughter are analysed at call and bout levels. Data of natural laughter is examined using electroglottograph (EGG) and acoustic signals. Nonspeech-laugh and laughed-speech are analysed in comparison with normal speech using features derived from the EGG and acoustic signals. Analysis of EGG signal is used to derive the average closed phase quotient in glottal cycles and the average instantaneous fundamental frequency (F0). Excitation source characteristics are analysed from the acoustic signal using a modified zero-frequency filtering (mZFF) method. Excitation impulse density and the strength of impulse-like excitation are extracted from the mZFF signal. Changes in the vocal tract system characteristics are examined in terms of the first two dominant frequencies derived using linear prediction (LP) analysis. Additional excitation information present in the acoustic signal is examined using a measure of sharpness of peaks in the Hilbert envelope of the LP residual at the glottal closure instants. Parameters representing degree of change and temporal changes in the production features are also derived to study the discriminating characteristics of laughter from normal speech. Changes are larger for nonspeech-laugh than laughed-speech, with reference to normal speech.

Immediate Effects of Humming on Computed Electroglottographic Parameters in Patients With Muscle Tension Dysphonia

To investigate the immediate effects of humming and subsequent um-hum phonation on the computed parameters of electroglottographic (EGG) signals in muscle tension dysphonia (MTD) patients and nondysphonic speakers. We included 21 MTD participants exhibiting both vocal roughness and supraglottic compression, who were able to produce successful humming and um-hum phonation. Twenty nondysphonic participants were selected as controls. Each participant was instructed to perform three phonatory tasks: natural phonation, humming phonation without pitch changes, and subsequent um-hum phonation, that is, humming with a pitch glide up as if agreeing with someone. Acoustic and EGG signals were recorded while the participants performed these tasks. Computed parameters reflecting the irregularities in vocal fold vibrations and the degree of glottal contact were calculated and compared between the tasks. The MTD group showed decreases in both perceptual vocal roughness and acoustic perturbation parameters while performing the tasks. The perturbation parameters of EGG signals and the standard deviation of the contact quotient (CQ) also exhibited significant decreases associated with either of humming or um-hum phonation in both groups. In addition, the CQ exhibited significant increases following humming alone in the MTD group and the combination of humming and um-hum phonation in both groups. These results suggest that the combination of humming without pitch changes and subsequent um-hum phonation have the immediate effect in adjusting the regularity of vocal fold vibration and augmenting the degree of glottal contact in MTD patients as well as nondysphonic speakers, whereas humming alone increases the degree of glottal contact in MTD patients.

Resonance tube phonation in water: High-speed imaging, electroglottographic and oral pressure observations of vocal fold vibrations - a pilot study

Phonation into glass tubes (‘resonance tubes’), keeping the free end of the tube in water, has been a frequently used voice therapy method in Finland and more recently also in other countries. The purpose of this exploratory study was to investigate what effects tube phonation with and without water has on the larynx. Two participants were included in the study. The methods used were high-speed imaging, electroglottographic observations of vocal fold vibrations, and measurements of oral pressure during tube phonation. Results showed that the fluctuation in the back pressure during tube phonation in water altered the vocal fold vibrations. In the high-speed imaging, effects were found in the open quotient and amplitude variation of the glottal opening. The open quotient increased with increasing water depth (from 2 cm to 6 cm). A modulation effect by the water bubbles on the vocal fold vibrations was seen both in the high-speed glottal area tracings and in the electroglottography signal. A second experiment revealed that the increased average oral pressure was largely determined by the water depth. The increased open quotient can possibly be explained by an increased abduction of the vocal folds and/or a reduced transglottal pressure. The back pressure of the bubbles also modulates glottal vibrations with a possible ‘massage’ effect on the vocal folds. This effect and the well-defined average pressure increase due to the known water depth are different from those of other methods using a semi-occluded vocal tract.

On transition between voice registers: Data from high-speed laryngeal videoendoscopy

How specific aspects of vocal fold vibration alter voice register has long been a subject of interest. Transitions between vocal registers are often studied using dynamic vocal fold models and electroglottographic signals. Although laryngeal high-speed videoendoscopy has also been applied to study steady-state voice registers, there has been little such investigation on the transitions between registers. In this study, we examined voice register transitions using phonations in which vocal qualities varied continuously in fundamental frequency (F0), loudness, or voice quality (from breathy to pressed). Glottal area measures {open quotient and alternating-current to open quotient ratios [Chen et al., JASA 133, 1656–1666 (2013)]} and acoustic measures (F0, energy, and H1-H2) were studied using simultaneously collected laryngeal high-speed videoendoscopy and audio recordings from 15 subjects. The video recordings were collected transorally at 10 000 frames per second. Glottal area waveforms were extracted using GlotAnTools (Version 5) [Erlangen, Germany], and acoustic measures were gathered using VoiceSauce software and analysis-by-synthesis. Glottal area measures were compared to acoustic measures and their relationships to voice register transitions were explored.

Investigating acoustic and electroglottograph features to characterize Passaggio in female singers

The purpose of this study was to examine the acoustic and electroglottographic features in the characterization of passaggio in female singers. Three groups of female singers were instructed to sing the notes of the scale for one octave using an ah vowel. When singing this octave they sang through a register shift, which is called passaggio. Their singing voices were recorded in a two-channel dataset. The first channel captured the acoustic signal using a microphone, and the second channel captured the electroglottographic (EGG) signal using an EGG instrument. A customized MatLab algorithm was designed to analyze the features of the two-channel dataset that contribute to the characterization of the passaggio in female singers. Glottal measurements can give robust information on precise glottal closing moments using the derivative of the EGG signal (dEGG) and speech acoustic waveform measurements can give similar information on glottal opening moments using the derivative of the audio signal (dAUDIO). The results of this investigation also provide an analytical framework for calculating these differentiated signals in female singers.