Volume 117, Issue 3, March 2005
Index of content:
- SPEECH PRODUCTION 
Simulations of temporal patterns of oral airflow in men and women using a two-mass model of the vocal folds under dynamic control117(2005); http://dx.doi.org/10.1121/1.1853235View Description Hide Description
In this study we use a low-dimensional laryngeal model to reproduce temporal variations in oral airflow produced by speakers in the vicinity of an abduction gesture. It attempts to characterize these temporal patterns in terms of biomechanical parameters such as glottal area, vocal fold stiffness, subglottal pressure, and gender differences in laryngeal dimensions. A two-mass model of the vocal folds coupled to a two-tube approximation of the vocal tract is fitted to oral airflow records measured in men and women during the production of /aha/ utterances, using the subglottal pressure,glottal width, and Q factor as control parameters. The results show that the model is capable of reproducing the airflow records with good approximation. A nonlinear damping characteristics is needed, to reproduce the flow variation at glottal abduction. Devoicing is achieved by the combined action of vocal fold abduction, the decrease of subglottal pressure, and the increase of vocal fold tension. In general, the female larynx has a more restricted region of vocal fold oscillation than the male one. This would explain the more frequent devoicing in glottal abduction–adduction gestures for /h/ in running speech by women, compared to men.
117(2005); http://dx.doi.org/10.1121/1.1842775View Description Hide Description
Low power, radarlike electromagnetic (EM) wave sensors, operating in a homodyne interferometric mode, are being used to measure tissue motions in the human vocal tract during speech. However, when these and similar sensors are used in front of the laryngeal region during voiced speech, there remains an uncertainty regarding the contributions to the sensor signal from vocal fold movements versus those from pressure induced trachea-wall movements. Several signal-source hypotheses are tested by performing experiments with a subject who had undergone tracheostomy, and who still was able to phonate when her stoma was covered (e.g., with a plastic plate). Laser-doppler motion-measurements of the subject’s posterior trachea show small tissue movements, about 15 microns, that do not contribute significantly to signals from presently used EM sensors. However, signals from the anterior wall do contribute. EM sensor and air-pressure measurements, together with 3-D EM wave simulations, show that EM sensors measure movements of the vocal folds very well. The simulations show a surprisingly effective guiding of EM waves across the vocal fold membrane, which, upon glottal opening, are interrupted and reflected. These measurements are important for EM sensor applications to speech signal de-noising, vocoding, speech recognition, and diagnostics.
117(2005); http://dx.doi.org/10.1121/1.1850074View Description Hide Description
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 SPLmeasurement 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).