One-dimensional static vocal tract model in the time domain

Abstract

The vocal tract can be modeled as an acoustic tube in the low-frequency region because the plane wave propagation is dominant. Further, it can be considered static for a limited short period during running speech, such as vowels. Thus, its acoustic properties have been examined mainly using the transmission line model (TLM), that is, the one-dimensional static model in the frequency domain. In the present paper, we propose a one-dimensional static model in the time domain based on the finite-difference time-domain method. In this model, the vocal tract is represented by the cascaded acoustic tubes of different cross-sectional areas. The pressure and wall vibration effects are simulated at the center of each tube. On the other hand, the volume velocity is calculated at the labial end. According to the leapfrog algorithm, the pressure and volume velocity are sequentially computed. As a result, the impulse responses of the vocal tracts for the five Japanese vowels were calculated, and the corresponding transfer functions agreed well with those calculated by the TLM in the low-frequency region. The mean absolute percentage difference of the lower four peaks for the five vowels was 2.3%.