Modeling the transitory behavior of speech using a time-varying transmission line

In this study, a transmission-line model of speech production [Rael et al., J. Acoust. Soc. Am. 97, S1(5) (1995)] is modified so that changes in the vocal-tract (VT) area functions, reflecting changes in the VT shape from one sound to another, are properly modeled. Each VT shape is divided into uniform cylindrical sections and each section is modeled by its equivalent transmission line comprising resistors (R), capacitors (C), and inductors (L). A radiation impedance terminates the transmission-line sections. For voiced sounds, the KLSYN88 glottal waveform [D. H. Klatt and L. C. Klatt, J. Acoust. Soc. Am. 87, 820–857 (1990)] is used as input. The model is simulated in time and frequency by using the analog-circuit simulator HSPICE. To simulate the transitory characteristics of speech, different interpolations such as linear, cubic, and Fourier transform are used for area transitions. The interpolated values result in a ‘‘sampled‘‘ area function and the RLC elements of each section are varied according to these time-sampled values. These variations are accomplished by utilizing time-varying independent voltage sources. Examples using American English dipthongs will be presented. Formant frequencies (both steady state and transitions) of the synthesized and natural dipthongs are in close agreement. [Work supported by NSF Award IRI-95-03089.]