Comparative assessment of electroglottographic and acoustic measures of jitter in pathological voices

Differences in shimmer across formant regions

OBJECTIVES

Objective acoustic measures used to analyze phonatory dysfunction include shimmer and jitter. These measures are limited in that they do not take into account auditory processing. However, previous studies have indicated that shimmer may be processed differently along the tonotopic axis of the ear and, in particular, may be perceptually and physiologically significant around the third and fourth formants.

METHODS

This study investigated the relationship between shimmer around the first four formants (F1-F4) and in the broadband unfiltered speech waveform for 18 normal speakers from the voice disorders database of KayPENTAX. The voice samples were filtered around each formant with a bandwidth of 400Hz and then shimmer was assessed using five built-in different measures from Praat software.

RESULTS

Comparisons of means tests revealed that shimmer increases significantly with formant frequency from F1 to F4, for all shimmer measures. Furthermore, for all shimmer measures, shimmer in the unfiltered speech was significantly and more strongly correlated with shimmer around F1 (r = 0.45-0.61) and F2 (r = 0.69-0.74), significantly but more weakly correlated with F4 (r = 0.42-0.47), and not significantly correlated with F3.

CONCLUSIONS

The findings indicate that there are differences in the shimmer found around the different formants and that shimmer information around F3 and F4 is not well captured in standard shimmer measurements based on the broadband unfiltered waveform.

Use of the rabbit larynx in an excised larynx setup

OBJECTIVE

To modify the excised larynx bench apparatus to accommodate experiments with rabbit larynges.

STUDY DESIGN

Methodological study using ex vivo rabbit larynges.

METHODS

Rabbit larynges (n=5) were dissected and mounted on a custom-made phonatory apparatus. The arytenoids were adducted by rods, and humidified air was passed through the larynx to elicit vocal fold vibration. Acoustic, aerodynamic, electroglottographic (EGG), and videokymographic data were collected for each larynx. The same data were collected for five canine larynges for the purpose of comparison, and coefficients of variation were calculated for each parameter in both models.

RESULTS

Reliable phonation was achieved in each larynx. Acoustic fundamental frequency (F(0)), percent jitter, percent shimmer, signal-to-noise ratio, pressure and flow at phonation onset and offset; and F(0), closed quotient, speed quotient, jitter, shimmer, and contact quotient, as recorded by EGG; and mucosal wave amplitude and phase difference are reported for rabbit larynges. Coefficients of variation for each parameter are similar in magnitude between the two models.

CONCLUSION

We developed a method for recording reliable acoustic, aerodynamic, videokymographic, and EGG data from rabbit larynges. When data obtained from leporine larynges were compared with data from canine larynges, the intralarynx variability of rabbit larynges was found to be similar to that of canine larynges.

Spectral moments of the long-term average spectrum: sensitive indices of voice change after therapy?

Voice clinicians require an objective, reliable, and relatively automatic method to assess voice change after medical, surgical, or behavioral intervention. This measure must be sensitive to a variety of voice qualities and severities, and preferably should reflect voice in continuous speech. The long-term average spectrum (LTAS) is a fast Fourier transform-generated power spectrum whose properties can be compared with a Gaussian bell curve using spectral moments analysis. Four spectral moments describe features of the LTAS: Spectral mean (Moment 1) and standard deviation (Moment 2) represent the spectrum's central tendency and dispersion, respectively. Skewness (based on Moment 3) and kurtosis (based on Moment 4) represent the spectrum's tilt and peakedness, respectively. To examine whether the first four spectral moments of the LTAS were sensitive to perceived voice improvement after voice therapy, this investigation compared pretreatment and posttreatment voice samples of 93 patients with functional dysphonia using spectral moments analysis. Inspection of the results revealed that spectral mean and standard deviation lowered significantly with perceived voice improvement after successful behavioral management (p < 0.001). However, changes in skewness and kurtosis were not significant. Furthermore, lowering of the spectral mean uniquely accounted for approximately 14% of the variance in the pretreatment to posttreatment changes observed in perceptual ratings of voice severity (p < 0.001), indicating that spectral mean (ie, Moment 1) of the LTAS may be one acoustic marker sensitive to improvement in dysphonia severity.

A computer system for acoustic analysis of pathological voices and laryngeal diseases screening

A system for acoustic analysis of pathological voices is proposed. The vocalized part of the voice signal is separated and all glottal cycles are traced by means of a cross-correlation detector. Based on the so determined beginning and duration of all glottal cycles, shimmer, jitter, several harmonics-to-noise ratios and other widely used acoustic parameters are calculated. New parameters are also introduced for estimation of the turbulent noise in voice signals (Turbulent Noise Index - TNI) and for the "breathy" voice characterization (Normalized First Harmonic Energy - NFHE). These parameters are applied for laryngeal pathology detection. An identification accuracy of 96.1% by the K-nearest neighbors' method has been achieved. The system is clinically tested.

On the influence of laryngeal pathologies on acoustic and electroglottographic jitter measures

This study compared acoustic and electroglottographic (EGG) jitter from [a] vowels of 103 dysphonic speakers. The EGG recordings were chosen according to their intensity, signal-to-noise ratio, and percentage of unvoiced intervals, while acoustic signals were selected based on voicing detection and the reliability of jitter extraction. The agreement between jitter measures was expressed numerically as a normalized difference. In 63.1% (65/103) of the cases the differences fell within +/-22.5%. Positive differences above +22.5% were associated with increased acoustic jitter and occurred in 12.6% (13/103) of the speakers. These were, typically, cases of small nodular lesions without problems in the posterior larynx. On the other hand, substantial rises in EGG jitter leading to differences below -22.5% took place in 24.3% (25/103) of the speakers and were related to hyperfunctional voices, creaky-like voices, small laryngeal asymmetries affecting the arytenoids, or small-to-moderate glottal chinks. A clinically relevant outcome of the study was the possibility of detecting gentle laryngeal asymmetries among cases of large unilateral increase in EGG jitter. These asymmetries can be linked with vocal problems that are often overlooked in endoscopic examinations.

Acoustic and physiologic characteristics of inspiratory phonation

Voice produced on inhaled air is a form of phonation that has received relatively little attention despite its apparent usefulness in the assessment of vocal function. This preliminary investigation was designed to describe the general characteristics of vocalization driven by an ingressive phonatory airflow. Vocal fundamental frequency (F0), electroglottographic (EGG), and airflow measures were examined in 16 normal men and women, who alternated between inspiratory and expiratory voice. Mean F0 routinely increased during inspiratory voice segments, shifting on average 5.1 semitones above the subjects' comfortable expiratory voice frequency. EGG data showed inspiratory voice to be associated with a more symmetrical pattern of vocal fold contact characterized by a prolonged interval of increasing contact. Both short-term F0 variability (jitter) and EGG amplitude perturbation were significantly higher during inspiratory voice. Stroboscopic examination of four of the subjects showed caudal displacement of the larynx and lengthened vocal folds associated with inspiratory phonation. The absolute airflow rate was significantly greater for inspiratory phonation, on average 48.5% higher than during normal expiratory voice. It was also found that both inspiratory pulse and falsetto vibratory patterns could be produced by at least some of the subjects, indicating some control over the mode and frequency of vocal fold vibration when driven by an ingressive airflow.