日本語単語アクセントの基本周波数パタンとその生成機構のモデル

抄録

Prosodic features in speech can be interpreted as responses of the underlying mechanisms to a set of linguistic commands. This paper presents a quantitative model for the mechanisms of generating fundamental frequency contours of word accent of standard Japanese. All the types of word accent of standard Japanese are characterized by the existence of a transition in the subjective pitch, either upward or downward, at the end of the initial mora, and by the fact that no more than one downward transition is allowed within a word. Table 1 lists are patterns of subjective pitch of all the possible accent types of words that consist of up to 5 morae. These binary patterns, however, never manifest as such in the fundamental frequency contours. Analysis of utterances of a number of speakers (Fig. 1) indicates that the logarithmic fundamental frequency contours of the same word accent, when normalized both in time and in frequency, are essentially similar(Fig. 2 and Fig. 3). These observations lead to the model of Fig. 4 based of the following assumptions:(1) Each type of word accent can be characterized by a unique logarithmic contour. (2) Commands for voicing and accent take the form of binary input to the system. (3) Separate mechanisms exist for voicing and accent, which can be approximated by linear system that convert the binary commands into the respective control signals(Fig. 5). (4) These control signals are combined and applied to the mechanism of glottal oscillation, whose fundamental frequency is an exponential function of the control signal. (5) The glottal mechanism shows hysteresis specified by the onset and cessation of the oscillation(Fig. 6). In order to investigate the validity of the model, fundamental frequency contours of various utterances of isolated words were extracted by a Computer program(Fig. 7) and were analyzed by the method of Analysis-by-Synthesis(Fig. ). A few examples of the comparison of the extracted fundamental frequency contour and its closest approximation obtained by the A-b-S procedure are shown in Fig. 9