Glottal Area Waveform Research Articles

Quantification of Videostrobolaryngoscopic Findings‐Measurements of the Normal Glottal Cycle

Videostrobolaryngoscopic (VSL) images of vocal fold behavior in 32 male and 33 female normal speakers were analyzed by computer. Image analysis software enhanced the glottal image, allowing extraction of the glottal area. Frame-by-frame analysis produced 20 glottal area values for each glottal cycle. The glottal area waveform (GAW) plots these values. From the GAW, features such as peak glottal area, duration of opening and closing, and rates of vocal fold opening and closing were measured. Acoustic measures of sound pressure level (SPL) and fundamental frequency were used to compare changes in GAW with changes in loudness and pitch. Analysis of the data showed significant differences between the sexes in GAW, peak glottal area, closed period, closing slope, and size and incidence of the posterior glottal gap. Intensity and frequency changes significantly affected GAW. Intensity variations affected the steepness of the closing phase and the duration of the closed period. Frequency changes affected the open period and the relative duration of opening vs. closing. This study provides quantitative measures of the VSL image that supplement and corroborate perceptual observations. These measures provide normative data against which similar measures of dysphonic larynges can be compared.

Effects of RLN and SLN stimulation on glottal area.

In vivo canine experiments have demonstrated that vocal fold stiffness varies proportionately with changing levels of recurrent laryngeal nerve (RLN) and superior laryngeal nerve (SLN) stimulation. This study evaluated the morphologic changes in the glottis at varying levels of nerve stimulation and the presumed effects on laryngeal air particle velocity. Stroboscopic data from the in vivo canine model of phonation were examined under varying conditions of RLN and SLN stimulation. Computerized analysis of stroboscopic images was used to reconstruct the glottal area vs. time waveforms. As RLN stimulation increased, glottal area per cycle decreased (p < 0.05). However, as SLN stimulation increased, glottal area per cycle increased (p < 0.05). However, as SLN stimulation increased, glottal area per cycle increased (p < 0.05). These results support the hypothesis that increasing RLN stimulation at similar levels of SLN stimulation produces an increase in air particle velocity, whereas an increase in SLN stimulation causes a decrease in air particle velocity.

Effects of RLN and SLN stimulation on glottic area.

In vivo canine experiments have demonstrated that vocal fold stiffness varies proportionately with changing levels of recurrent laryngeal nerve (RLN) and superior laryngeal nerve (SLN) stimulation. This study evaluates the morphologic changes in the glottis at varying levels of nerve stimulation and the effects on laryngeal resistance. Stroboscopic data from the invivo canine model were examined under varying conditions of RLN and SLN stimulation. Computerized analysis of stroboscopic images was used to reconstruct the glottic area versus time waveforms and the results will be presented. Glottal dynamics were measured using photoglottography, electroglottography, and the glottal area waveforms. The effects of varying RLN and SLN stimulation on laryngeal resistance will be discussed. [Work supported by an American Laryngologic Research Award.]

Source characteristics of diplophonia

Diplophonia describes the perception of more than one fundamental frequency component in a voice. Simultaneous photoglottographic (PGG), electroglottographic (EGG), and acoustic signals were collected from five diplophonic subjects. Results indicate that diplophonia is similar to the beat frequency phenomenon caused by independent vibration of the two vocal folds at slightly different frequencies. In the time domain, modeling vocal fold displacement from midline by summing two sine waves produced area waveforms closely resembling the PGG waveforms obtained from the diplophonic subjects. In the frequency domain, the diplophonic voice spectrum bears little resemblance to that of normal phonation. Instead of the normal set of harmonic peaks at integer multiples of the fundamental, the diplophonic spectrum shows a wealth of very closely spaced energy peaks of which the two fundamentals are often the most prominent but rarely the lowest frequency. The spectral envelope of the glottal area waveform may appear to have poles where no formants are possible and the spectral energy falls off quite rapidly. The locations of prominent energy peaks were predicted by modeling the displacement of the vocal folds from midline using the sum of two sine waves clipped by pulse trains to simulate collision effects of the two vocal folds. [Work supported by NINCDS.]

Nonlinear Inverse Filtering

It has been shown by Flanagan and Landgraf [IEEE Trans. Audio Electroacoust. 16, No. 1, 57–64 (1968)] that in the transformation between glottal area and glottal volume velocity during voiced vowels, the effect of the interaction between the acoustic impedance of the glottis and that of the supraglottal vocal tract cannot always be neglected. When there is such interaction, the glottal-supraglottal acoustic system must be considered a nonlinear system with time-varying parameters. Thus, any inverse-filtering process designed to extract the glottal area waveform from measurements of supraglottal pressure or air flow must also be nonlinear. This paper reports initial efforts to determine the conditions under which a nonlinear inverse-filtering process exists that will yield a function directly related to glottal area from recordings of oral volume velocity, and how such a nonlinear inverse filter could be implemented.

Vocal-Cord Spectra Derived from Glottal-Area Waveforms and Subglottal Photocell Monitoring

This paper reports a study wherein four subjects, phonating at two separate frequencies, were examined by photocell monitoring and simultaneous ultrahigh-speed photography. The glottal area waveforms from the film and the photocell output waveforms were compared by Fourier analyses. Comparisons of the two spectral displays confirm the findings of previous investigators, in that while the two methods produce similar waveforms, particularly of the same period, differences exist in the spectral properties of the waveforms thus derived. Differences in spectra may be attributed to phase-angle variations in the photocell monitor, or other such variables. Basic requirements for a photocell system with acceptable reliability are described.

Analysis-Synthesis of Glottal Excitation

A high-speed motion picture was used to obtain the time-dependent glottal opening for a speaker phonating /a/. The pressure waveform measured by a microphone at the speaker's lips was also recorded on film simultaneously with the glottal opening. A digital computer with a scope and light-pen facility was used to extract the glottal area and pressure waveform on a frame by frame basis. Van den Berg's relation for the resistance of the glottis to steady air flow was then used to calculate the time-dependent glottal volume velocity. The volume velocity was then used to excite a POVO. The output from the POVO was compared with the pressure waveform recorded during phonation. Volume velocities calculated for different subglottal pressures and a “standard” triangular waveform were also used to excite the POVO. Psychoacoustic evaluations were made of the natural quality of the various synthesized outputs.

Some Measurements of the Glottal-Area Waveform

High-speed motion pictures of the larynx were exposed by the techniques of indirect laryngoscopy at approximately 10 000 frames/sec. The acoustic waveform at the speaker's lips was also optically recorded on the film. The area of the glottal opening and amplitude of the acoustic waveform were measured, with the aid of a digital computer, for each frame of a film in which the speaker uttered /ɑ/ for approximately 0.3 sec. This short-voiced sound is about the duration of the voiced segments that normally occur in fluent speech. The changes of the glottal-area waveform are correlated with the beginning and end of phonation and the positions of the arytenoid cartilages.