Dept. of Electron., Kanazawa Inst. Tech. KIT), 7-1 Ohgigaoka, Nonoichi-Machi, Kanazawa-Minami, 921 Japan
This paper proposes a simple model of generating time series of F0 (fundamental frequency) fluctuation of voice from the viewpoint of the dynamical systems generating the irregularity. The data examined were the F0 fluctuation for two kinds of voice, the normal and the pathological (perceived as ``rough''). The time series of F0 were obtained from the speech waveform of sustained utterances. The voice samples analyzed were for 20 normal (for five male and three female subjects) and 39 pathological (rough) (for sixteen male and one female subjects). By examining the time series and the pseudo-phase-portraits, a simple two-dimensional mathematical model generating the time series of fluctuation is proposed by combining the characteristics of the Henon map (``folding'' operation) and the Delayed logistic map (``twisting'' operation). Using the model, basic aspects of the fluctuations as well as of the pseudo-phase-portraits are successfully described with a single control parameter. The model simulation also suggests that a resultant intermittent type of fluctuation manifests a chaotic behavior which is actually observed in a pathological rough voice. The transition of fluctuation from the normal voice to the pathological voice is simulated by this model.