The 1994 Abbot hybrid connectionist-HMM large vocabulary recognition system.
ABBOT is the hybrid connectionist-hidden Markov model largevocabulary speech recognition system developed at Cambridge University. In this system, a recurrent network maps each acoustic vector to an estimate of the posterior probabilities of the phone classes. The maximum likelihood word string is then extracted using Markov models. As in traditional hidden Markov models, the Markov process is used to model the lexical and language model constraints. This paper describes the system which participated in the November 1994 ARPA evaluation of continuous speech recognition systems. The emphasis of the paper is on the differences between the 1993 and 1994 versions of the ABBOT system. This includes the utilization of a larger training corpus (SI284 versus SI84), the extension of the lexicon from 5,000 words to 65,000 words, the application of a trigram language model, and the development of a near-realtime single-pass decoder well suited for the hybrid approach. Experimental results are reported for various test and development sets from the November 1992, 1993 and 1994 ARPA benchmark tests.