Pole-zero determination of the vocal-tract transfer function

The transfer function of the vocal tract T(f) is defined as the ratio of the volume velocity at the mouth opening and the sound pressure of the source. In general, this transfer function T(f) can be described by conjugate complex pairs of poles and zeros. This paper describes new efforts in the accurate estimation of the pole- and zero-location (frequency and bandwidth). The procedure is performed by an appropriate computer program. As the spectrum is plotted on a computer display, the human operator is given the possibility to mark areas of interest by light-pen. From the spectrum a first estimate of the frequency and bandwidth is evaluated by calculating the maximum (or minimum) of the transfer function in a given area and the width of its 3-dB slope. A subsequent variation of the frequency and bandwidth leads to an accurate evaluation of the pole or zero location in the s-plane. The variation strategy used by the computer and results are presented in this paper.