Martin Oerder

Improvements in beam search for 10000-word continuous speech recognition

The author describes the improvements in a time synchronous beam search strategy for a 10000-word continuous speech recognition task. The improvements are based on two measures: a tree-organization of the pronunciation lexicon and a novel look-ahead technique at the phoneme level, both of which interact directly with the detailed search at the state levels of the phoneme models. Experimental tests were performed for four speakers on a 12306-word task. As a result of the above measures, the overall search effort was reduced by a factor of 17 without a loss in recognition accuracy.<<ETX>>

Word graphs: an efficient interface between continuous-speech recognition and language understanding

Word graphs are directed acyclic graphs where each edge is labeled with a word and a score, and each node is labeled with a point in time. Word graphs form an efficient feedforward interface between continuous-speech recognition and linguistic processors. Word graphs with high coverage and modest graph densities can be generated with a computational load comparable with bigram best-sentence recognition. Results on word graph error rates and word graph densities are presented for the ASL (Architecture Speech/Language) benchmark test.<<ETX>>

The Philips Research system for continuous-speech recognition

This paper gives an overview of the Philips Research system for continuous-speech recognition. The recognition architecture is based on an integrated statistical approach. The system has been successfully applied to various tasks in American English and German, ranging from small vocabulary tasks to very large vocabulary tasks and from recognition only to speech understanding. Here, we concentrate on phoneme-based continuous-speech recognition for large vocabulary recognition as used for dictation, which covers a significant part of our research work on speech recognition. We describe this task and report on experimental results. In order to allow a comparison with the performance of other systems, a section with an evaluation on the standard North American Business news (NAB2) task (dictation of American English newspaper text) is supplied.

A spoken language inquiry system for automatic train timetable information

Abstract This article describes the Philips automatic train timetable information system which enables the user to call up accurate information about train connections between 1200 German cities over the telephone. In contrast to most of the inquiry systems available so far, the caller can talk to our system in unrestricted, natural and fluent speech, very much like talking to a human operator. No instructions are given beforehand. The system consists of four main components: speech recognition, speech understanding, dialogue control, and speech output. They are separated into independent modules and executed sequentially. The speech recogniser creates a word graph from the spoken input. This word graph is then passed to the understanding component which computes the meaning, using an attributed stochastic context-free grammar. A dialogue manager analyses the results and either accesses the database or comes up with another question if necessary. The system has been made available to the general public in an ongoing field test, both to gather speech data and to evaluate its performance.

Continuous speech dictation: from theory to practice

This paper gives an overview of the Philips research system for phoneme-based, large-vocabulary, continuousspeech recognition. The system has been successfully applied to various tasks in the German and (American) English languages, ranging from small vocabulary tasks to very large vocabulary tasks. Here, we concentrate on continuousspeech recognition for dictation in real applications, the dictation of legal reports and radiology reports in German. We describe this task and report on experimental results. We also describe a commercial PC-based dictation system which includes a PC implementation of our scientific recognition prototype. In order to allow for a comparison with the performance of other systems, a section with an evaluation on the standard Wall Street Journal task (dictation of American English newspaper text) is supplied. The recognition architecture is based on an integrated statistical approach. We describe the characteristic features of the system as opposed to other systems: 1. the Viterbi criterion is consistently applied both in training and testing; 2. continuous mixture densities are used without tying or smoothing; 3. time-synchronous beam search in connection with a phoneme look-ahead is applied to a tree-organized lexicon.

Kontextabhängige Phonemmodelle bei der Erkennung kontinuierlicher Sprache in verschiedenen Szenarien

Der Gebrauch von Triphonen fur die kontextabhangige akustische Modellierung ist zu einer etablierten Methode fur die Erkennung kontinuierlicher Sprache bei grosem Vokabular geworden. Deutliche Reduzierungen der Wortfehlerrate sind berichtet worden [3] [1], Wir werden hier jedoch zeigen, das diese Ergebnisse sehr von der fur die Messung der Fehlerrate verwendeten Datenbasis abhangen. Fur unser Erkennungssystem (12000 Worter) und eine Datenbasis mit deutschen Geschaftsbriefen konnte nur eine geringfugige Verringerung der Fehlerrate beobachtet werden.