Focus and Accent in a Dutch Text-to-Speech System

FOCUS AND ACCENT IN A DUTCH TEXT.TO-SPEECH SYSTEM Joan LG. Baart Phonetics Laboratory, Department of General Linguistics Cleveringaplaats 1, P.O~Box 9515 2300 RA Leiden, The Netherlands Abstract In this paper we discuss an algorithm for the assignment of pitch accent positions in text-to-speech conversion. The algorithm is closely modeled on current linoulstic accounts of accent placement, and assumes a surface syntactic analysis of the input. It comprises a small number of heuristic rules for determining which phrases of a sentence are to be focussed upon; the exact location of a pitch accent within a focussed phrase is determined m~inly on the basis of the syntactic relations holding between the elements of the phrase. A perceptual evaluation experiment showed that the algorithm proposed here leads to improved subjective speech quality as compared to a naive algorithm which accents all and only content words. 1. Introduction This paper deals with the prosodic com- ponent of a text-to-speech system for Dutch, more in particular with the rules for assign- ing pitch accents (sentence accents) to words in an input sentence. Whereas other work on accent rules for Dutch speech synthesis (Kager & Quen6, 1987) did not assume a syntactically analysed input, I will here work from the assumption that the text-to-speech system has a large dictionary as well as a syntactic parser at its disposal. The paper is organized as follows: in section 2 I shortly introduce the notions focus and (pitch) accent as I will be using them; as my framework, I will choose the Eindhoven model of Dutch intonation Ct Hart & Cohen, 1973; 't Hart & Collier, 1975) in conjunction with Gussenhoven's (1983) accent placement theory. In section 3 I discuss the rules that connect a domain of focus to an accent on a particular word. The assi~mment of focus domMn~ is dealt with in section 4. At the end of this section I s-mrn~O my proposals in the form of an accent assignment algorithm~ In section 5 I present some results obtained in a perceptual evaluation of this al- gorithm. 2. A two-stage model of accent placement Work on Dutch intonation at the In- stitute for Perception Research (IPO) in Eindhoven has resulted in an inventory of elementary pitch movements that make up the occurring Dutch intonation contours ('t Hart & Cohen, 1973; 't Hart & Comer, 1975). The phonetic characteristics of these pitch movements are known precisely, and this knowledge can be used in the synthesis of natural-sounding Dutch intonation contours. It was found that some of these elementary pitch movements cause the syllable on which they are executed to be perceived as ac- cented. I will use the term pitch accent or simply accent to refer to prominence caused by the presence of such an accent-lending pitch movement. Of course, the intonation model does not predict where in a sentence pitch accents or intonational boundaries will be located, but when these locations are provided as input, the model is capable of generating a natural-sounding contour. In the …

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