A frame language for the control of phonetic decoding in continuous speech recognition

The acoustic-phonetic decoding of a sentence is a major bottleneck in continuous speech recognition. Our group has been working in this area for the past twelve years and has developed several systems relying on synchronous centi-second pattern matching techniques and on rule-based phoneme segmentation and identification. We propose in this paper a new method for knowledge representation and use in phonetic decoding of continuous speech. Our system is based on the notion of frame. This formalism makes it possible to use different types of acoustic analyses and of phonetic features and also to control the recognition process by a planning system. This latter point corresponds to a more sophisticated control than in classical systems. This planning system is described by a frame grammar which is described in details in the paper. This system has been designed in close relation with a phonetic decoding expert system called SYSTEXP described in the 1984 ICASSP Proceedings. SYSTEXP formalizes the expertise of a human phonetician reading speech spectrograms in terms of rules and meta-rules. The results obtained in this manner are used in our frame system in order to obtain a reliable, multi-speaker segmentation of the speech wave into phonemic units, and to apply the phonetic knowledge for phoneme identification. This paper gives an insight description of the principles of the system and of the system itself, including the frame language. It also presents and discusses the recognition results which have been already obtained and which show the interest of the method.