Jan G. Švec

Videokymography: High-speed line scanning of vocal fold vibration

A digital technique for high-speed visualization of vibration, called videokymography, was developed and applied to the vocal folds. The system uses a modified video camera able to work in two modes: high-speed (nearly 8,000 images/s) and standard (50 images/s in CCIR norm). In the high-speed mode, the camera selects one active horizontal line (transverse to the glottis) from the whole laryngeal image. The successive line images are presented in real time on a commercial TV monitor, filling each video frame from top to bottom. The system makes it possible to observe left-right asymmetries, open quotient, propagation of mucosal waves, movement of the upper and, in the closing phase, the lower margins of the vocal folds, etc. The technique is suitable for further processing and quantification of recorded vibration.

First results of clinical application of videokymography

Objectives: Stroboscopy is based on the assumption that the vibration of the vocal folds is stable and regular. Irregular vibrations, which are common in voice pathology, cannot easily be studied and described in a reliable way. Videokymography overcomes most of these drawbacks. Design: The use of the recently invented videokymography for studying vocal fold vibrations in patients is introduced. Method: Videokymography, using a modified CCD‐video camera, works in two modes: standard and high speed. In standard mode the vocal folds are displayed on a video monitor in the usual way, providing 50 images per second (or 60 in the National Television Standards Committee (NTSC) system). This is used for routine laryngoscopic and stroboscopic examination of the larynx. In high‐speed mode (nearly 8000 images per second) only one line from the whole image is selected and displayed on the x‐axis of the monitor; the y‐axis represents the time dimension. Results: All kinds of vocal fold vibrations, including those leading to pathological rough, breathy, hoarse, or diplophonic voice productions can be observed. Videokymography visualizes small left‐right asymmetries, open quotient differences along the glottis, lateral propagation of mucosal waves, and movements of the upper margin and, sometimes in the closing phase, the lower margin of the vocal folds. Conclusion: Videokymography is advantageous for a more accurate diagnosis of voice disorders. Videokymography provides a simple way to study irregular vibrations of the vocal folds. Information is directly available for further processing and allows a first‐time quantification of vibrations registered.

Voicing and silence periods in daily and weekly vocalizations of teachers

The National Center for Voice and Speech (NCVS) data bank on voice dosimetry was used to study the distributions of continuous voicing periods and silence periods in 31 teachers over the duration of two weeks. Recordings were made during all awake hours of the day. Voicing periods were grouped into half decades, ranging from 0.0316 to 0.10 s for the shortest periods of phonation to 31.6-100 s for the longest periods of phonation. Silence periods were grouped into similar half decades, but ranged up to periods of several hours. On average, the teachers had 1800 occurrences of voicing (onset followed by offset) per hour at work and 1200 occurrences per hour while not at work. Voicing occurred 23% of the total time at work, dropping to 13% during off-work hours and 12% on weekends. The greatest accumulation of voicing occurred in the 0.316-1.0 s voicing periods, whereas the greatest accumulation of silence occurred in the 3-10 s silence periods. The study begins to lay the groundwork for understanding vocal fatigue in terms of repetitive motion and collision of tissue, as well as recovery from such mechanical stress.

Estimation of sound pressure levels of voiced speech from skin vibration of the neck

How accurately can sound pressure levels (SPLs) of speech be estimated from skin vibration of the neck? Measurements using a small accelerometer were carried out in 27 subjects (10 males and 17 females) who read Rainbow and Marvin Williams passages in soft, comfortable, and loud voice, while skin acceleration levels (SALs) and SPLs were simultaneously registered and analyzed every 30 ms. The results indicate that the mean SPL of voiced speech can be estimated with accuracy better than +/-2.8 dB in 95% of the cases when the subjects are individually calibrated. This makes the accelerometer an interesting sensor for SPL measurement of speech when microphones are problematic to use (e.g., noisy environments or in voice dosimetry). The estimates of equivalent SPL, which is the logarithm of averaged relative energy of voiced speech, were found to be up to 1.5 dB less accurate than the mean SPL. The estimation accuracy for instantaneous SPLs was worse than for the mean and equivalent SPLs (on average +/-6 and +/-5 dB for males and females, respectively).

Measurement of vocal doses in speech: experimental procedure and signal processing.

An experimental method for quantifying the amount of voicing over time is described in a tutorial manner. A new procedure for obtaining calibrated sound pressure levels (SPL) of speech from a head-mounted microphone is offered. An algorithm for voicing detection (kv) and fundamental frequency (F0) extraction from an electroglottographic signal is described. The extracted values of SPL, F0, and kv are used to derive five vocal doses: the time dose (total voicing time), the cycle dose (total number of vocal fold oscillatory cycles), the distance dose (total distance travelled by the vocal folds in an oscillatory path), the energy dissipation dose (total amount of heat energy dissipated in the vocal folds) and the radiated energy dose (total acoustic energy radiated from the mouth). The doses measure the vocal load and can be used for studying the effects of vocal fold tissue exposure to vibration.An experimental method for quantifying the amount of voicing over time is described in a tutorial manner. A new procedure for obtaining calibrated sound pressure levels (SPL) of speech from a head-mounted microphone is offered. An algorithm for voicing detection (kv) and fundamental frequency (F0) extraction from an electroglottographic signal is described. The extracted values of SPL, F0, and kv are used to derive five vocal doses: the time dose (total voicing time), the cycle dose (total number of vocal fold oscillatory cycles), the distance dose (total distance travelled by the vocal folds in an oscillatory path), the energy dissipation dose (total amount of heat energy dissipated in the vocal folds) and the radiated energy dose (total acoustic energy radiated from the mouth). The doses measure the vocal load and can be used for studying the effects of vocal fold tissue exposure to vibration.

Vocal Tract and Glottal Function During and After Vocal Exercising With Resonance Tube and Straw

OBJECTIVE The present study aimed to investigate the vocal tract and glottal function during and after phonation into a tube and a stirring straw. METHODS A male classically trained singer was assessed. Computerized tomography (CT) was performed when the subject produced [a:] at comfortable speaking pitch, phonated into the resonance tube and when repeating [a:] after the exercise. Similar procedure was performed with a narrow straw after 15 minutes silence. Anatomic distances and area measures were obtained from CT midsagittal and transversal images. Acoustic, perceptual, electroglottographic (EGG), and subglottic pressure measures were also obtained. RESULTS During and after phonation into the tube or straw, the velum closed the nasal passage better, the larynx position lowered, and hypopharynx area widened. Moreover, the ratio between the inlet of the lower pharynx and the outlet of the epilaryngeal tube became larger during and after tube/straw phonation. Acoustic results revealed a stronger spectral prominence in the singer/speakers formant cluster region after exercising. Listening test demonstrated better voice quality after straw/tube than before. Contact quotient derived from EGG decreased during both tube and straw and remained lower after exercising. Subglottic pressure increased during straw and remained somewhat higher after it. CONCLUSION CT and acoustic results indicated that vocal exercises with increased vocal tract impedance lead to increased vocal efficiency and economy. One of the major changes was the more prominent singers/speakers formant cluster. Vocal tract and glottal modifications were more prominent during and after straw exercising compared with tube phonation.

Vocal tract changes caused by phonation into a tube: a case study using computer tomography and finite-element modeling.

Phonation into a glass tube is a voice training and therapy method that leads to beneficial effects in voice production. It has not been known, however, what changes occur in the vocal tract during and after the phonation into a tube. This pilot study examined the vocal tract shape in a female subject before, during, and after phonation into a tube using computer tomography (CT). Three-dimensional finite-element models (FEMs) of the vocal tract were derived from the CT images and used to study changes in vocal tract input impedance. When phonating on vowel [a:] the data showed tightened velopharyngeal closure and enlarged cross-sectional areas of the oropharyngeal and oral cavities during and after the tube-phonation. FEM calculations revealed an increased input inertance of the vocal tract and an increased acoustic energy radiated out of the vocal tract after the tube-phonation. The results indicate that the phonation into a tube causes changes in the vocal tract which remain also when the tube is removed. These effects may help improving voice production in patients and voice professionals.

Comparison of biomechanical modeling of register transitions and voice instabilities with excised larynx experiments.

Voice instabilities were studied using excised human larynx experiments and biomechanical modeling. With a controlled elongation of the vocal folds, the experiments showed registers with chest-like and falsetto-like vibrations. Observed instabilities included abrupt jumps between the two registers exhibiting hysteresis, aphonic episodes, subharmonics, and chaos near the register transitions. In order to model these phenomena, a three-mass model was constructed by adding a third mass on top of the simplified two-mass model. Simulation studies showed that the three-mass model can vibrate in both chest-like and falsetto-like patterns. Variation of tension parameters which mimic activities of laryngeal muscles could induce transitions between both registers. For reduced prephonatory areas and damping constants, extended coexistence of chest and falsetto registers was found, in agreement with experimental data. Subharmonics and deterministic chaos were observed close to transitions between the registers. It is concluded that the abrupt changes between chest and falsetto registers can be understood as shifts in dominance of eigenmodes of the vocal folds.

Resonance properties of the vocal folds: In vivo laryngoscopic investigation of the externally excited laryngeal vibrations

The study presents the first attempt to investigate resonance properties of the living vocal folds by means of laryngoscopy. Laryngeal vibrations were excited via a shaker placed on the neck of a male subject and observed by means of videostroboscopy and videokymography (VKG). When the vocal folds were tuned to the phonation frequency of 110 Hz and sinusoidal vibration with sweeping frequency (in the range 50-400 Hz) was delivered to the larynx, three clearly pronounced resonance peaks at frequencies around 110, 170, and 240 Hz were identified in the vocal fold tissues. Different modes of vibration of the vocal folds, observed as distinct lateral-medial oscillations with one, two, and three half-wavelengths along the glottal length, respectively, were associated with these resonance frequencies. At the external excitation frequencies below 100 Hz, vibrations of the ventricular folds, aryepiglottic folds and arytenoid cartilages were dominant in the larynx.

Electroglottographic Study of Seven Semi-Occluded Exercises: LaxVox, Straw, Lip-Trill, Tongue-Trill, Humming, Hand-Over-Mouth, and Tongue-Trill Combined With Hand-Over-Mouth

INTRODUCTION Semi-occluded vocal tract exercises (SOVTE) are often used in voice clinics. SOVTE change the acoustic vocal tract impedance in relation to the glottis impedance, improving voice quality. However, differences among SOVTE, such as the number of vibration sources into the vocal tract, are often disregarded by clinicians. Some SOVTE present single, whereas others double source. This study aims at investigating changes in voice production pattern for a series of SOVTE. A combined exercise (tongue-trill coupled with hand-over-mouth) was implemented to illustrate the effect of a secondary source of vibration in the vocal tract. METHOD Twenty-three healthy volunteers performed a series of SOVTE: LaxVox, straw, lip-trill, tongue-trill, hand-over-mouth, humming, and tongue-trill combined with hand-over-mouth. Comfortable phonation served as control exercise. The dependent variables were electroglottography contact quotient (CQ), contact quotient range (CQr), fundamental frequency (F0), fundamental frequency range, and difference between the first formant frequency and F0 (F1 - F0). RESULTS A significant difference for CQr scores compared with comfortable phonation was found for the combined tongue-trill with hand-over-mouth, lip-trill, LaxVox, and tongue-trill exercises. The F1 - F0 acoustic analysis showed significant differences in scores for exercises with one versus two sources of vibration. DISCUSSION AND CONCLUSION The results indicate that SOVTE should be divided into two groups, as follows: (a) steady (single sourced) with lower CQr and F1 - F0 difference (hand-over-mouth, humming, and straw) and (b) fluctuating (dual source) with larger CQr and F1 - F0 difference (tongue-trill, lip-trill, and LaxVox). Because of these differences, also different therapeutic effects can be expected. Tongue-trill combined with hand-over-mouth exhibited mixed effects of both the exercise groups.