Digital analysis of laryngeal control in speech production

Abstract

Physiological measurements are made directly on human talkers to determine several dynamic laryngeal functions. The functions are control variables in a speech synthesizer which utilizes acoustic models of the vocal cords and vocal tract. The functions are measured simultaneously and recorded on multichannel FM tape. They are the time variation of vocal-cord (glottal) opening (Ag); the electromyographic (EMG) potentials of three laryngeal muscles−−posterior crico-arytenoid (PCA), interarytenoid (IA), and crico-thyroid (CT); the subglottal air pressure (Ps); the speech output sound pressure waveform (P); and timing pulses from a digital clock. Preliminary data for ten utterances by a man are digitized by a multiplexed A/D converter on a DDP−516 computer, and the results are stored in disk file for analysis. Bandwidth of the multitrack FM playback is 2800 Hz. Each function is sampled at 6250 sec−1 and quantized to 16 bits. Digital filtering is applied to remove dc offsets and enhance information features. The acoustic functions (Ag, Ps, and P) are submitted to programmed pitch analysis. The results show how voice periodicity can be manifested differently at the glottal and sound-output levels. A typical instance is vocal-cord vibration throughout the occluded phase of a voiced stop consonant. The EMG functions are analyzed by computing short-time energy. The results are correlated with voicing onset/offset and with voice pitch. PCA energy is shown to be correlated with voicing offset, and anticipatory to it by about 20–30 msec. IA energy is shown to be correlated with voicing onset, and anticipatory to it by about 40–50 msec. CT energy is found to be nearly directly correlated with the frequency contour for voice pitch. Direct utilization of these physiological parameters for speech synthesis is suggested. Subject Classification: [43]70.20, [43]70.60.