The LIMSI 1995 Hub3 System

In this paper we report on the LIMSI recognizer evaluated in the ARPA 1995 North American Business (NAB) News Hub 3 benchmark test. The LIMSI recognizer is an HMM-based system with Gaussian mixture. Decoding is carried out in multiple forward acoustic passes, where more refined acoustic and language models are used in successive passes and information is transmitted via word graphs. In order to deal with the varied acoustic conditions, channel compensation is performed iterativel y, refining the noise estimates before the first three decoding passes. The final decoding pass is carried out with speaker-adapted models obtained via unsupervised adaptation using the MLLR method. In contrast to previous evaluations, the new Hub 3 test aimed at improving basic SI, CSR performance on unlimited-vocabulary read speech recorded under more varied acoustical conditions (b ackground environmental noise and unknown microphones). On the Sennheiser microphone (average SNR 29dB) a word error of 9.1% was obtained, which can be compared to 17.5% on the secondary microphone data (average SNR 15dB) using the same recognition system.

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