Calibration of external lighting and sensing photoglottograph

Observation and measurement of vocal folds vibration and glottal opening during speech requires techniques as little invasive as possible for the subject. The LPP has developed the External Photoglottograph (ePGG) system. It consists of illuminating the glottis through the neck skin with an infrared light and recording light variation intensity modulated by glottal movement with a photodiode placed across the larynx. The system is tested on two mechanical larynx replicas. The first one consists of two rigid half cylinders in forced oscillation controlled by a step motor. The second one is flow driven and uses latex tubes filled with water in order to reproduce vocal folds self-oscillation. Time-varying glottal area is measured accurately for both replicas. Experimental results are compared to ePGG recordings in order to assess the correlation between area measurements and ePGG signal. This characterization is used to propose a calibration of the glottal opening as a function of parameters affecting the ePGG signal (distance, angle, skin, tissue, system setting, etc.).