Japanese Prosodic Phrasing and Intonation Synthesis

JAPANESE PROSODIC PHRASING AND INTONATION SYNTHESIS Mary E. Beckman 1 and Janet B. Pierrehnmbert Linguistics and Artificial Intelligence Research AT&T Bell Laboratories, 600 Mountain Ave, Murray Hill, NJ 07974 ABSTRACT A computer program for synthesizing Japanese fundamental frequency contours implements our theory of Japanese intonation. This theory provides a complete qualitative description of the known characteristics of Japanese intonation, as well as a quantitative model of tone-scaling and timing precise enough to translate straightforwardly into a computational algorithm. An important aspect of the description is that various features of the intonation pattern are designated to be phonological properties of different types of phrasal units in a hierarchical organization. This phrasal organization is known to play an important role in parsing speech. Our research shows it also to be one reflex of intonational prominence, and hence of focus and other discourse structures. The qualitative features of each phrasal level and their implementation in the synthesis program are described. 1. INTRODUCTION In this paper, we will present a computer program for synthesizing fundamental frequency contours for standard Japanese. Fundamental frequency (fO) is the paramount physical correlate of the sensation of pitch, and, in many languages, the time course of f0 is one of the primary phonetic manifestations of intonation. This is especially true in Japanese, where duration and amplitude do not have the consequential role in communicating intonational structure that they do in English (Beckman, 1986). Accordingly, a program for synthesizing Japanese f0 contours is tantamount to a computational implementation of a theory of Japanese intonation. The theory that we have implemented in our synthesis program is based on a review of the literature in English and Japanese, and on the results of an extensive series of experiments in which we examined and made f0 measurements of about 2500 intonation contours in order to resolve some of the many problems not answered in the literature. These experiments have uncovered important facts about the hierarchical structure underlying Japanese prosody and about the manifestations of focus in Japanese. We have incorporated these discoveries in our synthesis program, which, we believe, covers all known qualitative characteristics of Japanese intonational melody. Informal listening tests by Japanese speakers indicate that the f0 contours which the program produces sound quite natural. In some cases, the synthesized contours were even preferred to the genuine human intonation contours on which they are modeled. Although the main concern of our research was to provide an accurate phonological and phonetic characterization of Japanese intonational structure that could be used in the automatic computation of f0 contours, our description of Japanese prosodic phrasing and intonation synthesis is also of direct relevance to issues in several other areas, including the role of prosodic 1. Present address: Ohio State University, Department of Linguistics, 1841 Millikin Rd, Columbus, OH 43210. phrasing in the parsing of speech, the relationship between intonational patterns and discourse phenomena such as focus, and the development of a more accurate understanding of the phonological mechanisms of intonation as a universal component of …

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