Estimation of glottal waves based on nonminimum phase models

Abstract

Research on the glottal wave has been widely carried out because the characteristic of glottal wave generated by the vibration of a glottis greatly influences the quality of synthesized voice. Since it has been known that the waveforms of the glottal wave are asymmetric triangles with rounded corners, sound sources which parametrically express the glottal wave have been proposed. In these sound models, the characteristics of glottal waves in various cases must be known. In order to estimate the glottal wave from the observed voice signal, the inverse-filter method, in which an inverse filter with an inverse characteristic of the voice transfer function is used, has been widely developed. However, since the voice path transfer function and glottal wave are independently estimated in this method, error occurs and it is not an easy task to eliminate the error. This paper proposes a novel algorithm which simultaneously estimates the voice path transfer function and characteristic of the glottal wave. In this algorithm, the voice generation process is expressed by a nonminimum phase model including the characteristic of glottal wave, and the glottal wave is estimated by obtaining the parameters of the transfer function. In order to estimate the glottal wave, not only an estimation of the parameters of the transfer function but also an unknown driving input signal must be known. However, since the inverse system of the transfer function becomes unstable in this method based on the nonminimum phase model, an approximate inverse system is adopted. Then, when the characteristic of the voice path is given by an all-pole model, the glottal wave can be estimated. The nonminimum phase model by this method can be used for voice synthesis based on the glottal wave. The glottal wave was estimated by simulation and observing the sound of vowels, and it was found that this estimation algorithm was effective. © 1997 Scripta Technica, Inc. Electron Comm Jpn Pt 3, 80(9): 59–69, 1997