Morphological Analysis for a German Text-to-Speech System

MORPHOLOGICAL ANALYSIS FOR A GERMAN TEXT-TO-SPEECH SYSTEM Amanda Pounder, Markus Kommenda Institut ffir Nachrichtentechnik und Hochfrequonztechnik Technische Universit/it Wien Gusshausstrasse 25, A-1040 Wien, Austria ABSTRACT A central problem in speech synthesis with unre- stricted vocabulary is the automatic derivation of correct pronunciation from the graphemic form of a text. The software module GRAPHON was developed to perform this conversion for German and is currently being extended by a morphological analysis compo- nent. This analysis is based on a morph lexicon and a sot of rule~ and structural descriptions for German word-forms. It provides each text input item with an individual characterization such that the phonological~ syntactic, and prosodic components may operate upon it. This systematic approach tht~s serves to minimize the number of wrong transcriptions and at the same time lays the foundation for the generation of stress and intonation patterns, yielding more intelligible~ natural-sounding, and generally acceptable synthetic speech. 1. INTRODUCTION Many applications of computer speech require unre- stricted vocabulary. In particular~ voice output units of this kind permit the linkage of the common tele- phone network to a central computer, thus enabling access for a large public. "Karlchen", the Frankfurt talking railway timetable, and other automatic infor- mation services are based on this principle. If a written text serves as input to a speech syn- thesis system with unrestricted vocabulary (text-to- speech synthesis)p the derivation of a correct and natural-sounding pronunciation and intonation must be provided for. The software module GRAPHON (GRAPHemo-PHONome-conversion) has boon developed to convert any given German text into its phonetic transcription (I.P.A.)~ enriched by some prosodic markers. The text-to-speech system is being implemented on an HP 9816 workstation system with a 68000 CPU and 768 kbyte of RAM. At present a SSI 263 phone syn- thesizer serves as acoustical output unit; a simplified articulatory model used to control a refined digital vocal tract synthesizer is under development. The software is written in PASCAL and operation of the whole system is expected to be almost real-time. (For further implementational details cf. [1].) While text-to-speech systems for the English lan- guage are fairly advanced, there is much room for development for German ~peaking systems. It is pos- sible only to a limited extent to profit from work in the field of English. Obviouslyj German pronunciation rules differ from those of other languages; however9 the mere replacement of a given grapheme-to-pho- neme conversion rule by another is inadequate to meet the demands of the very different principles on which two writing-systems are founded. Tills also applies to the structural levels of morphology and syntax. 2. MOTIVATION FOR A MORPHOIA)GICAL COMPONENT The application of an English pronunciation rule is lexically determined, that is to say, is restricted to a generally arbitrary subset of the lexicon (compare~ for example, the values of (eaY in the sets 4bread, head, thread...~ and {kneads bead, heat..,} ). It is for this reason that many English-based systems include very extensive dictionaries, for example the pioneer- ing work of Allen [2] with a 12000 …

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