Gareth L. Moore

The Cambridge University spoken document retrieval system

This paper describes the spoken document retrieval system that we have been developing and assesses its performance using automatic transcriptions of about 50 hours of broadcast news data. The recognition engine is based on the HTK broadcast news transcription system and the retrieval engine is based on the techniques developed at City University. The retrieval performance over a wide range of speech transcription error rates is presented and a number of recognition error metrics that more accurately reflect the impact of transcription errors on retrieval accuracy are defined and computed. The results demonstrate the importance of high accuracy automatic transcription. The final system is currently being evaluated on the 1998 TREC-7 spoken document retrieval task.

Automatic transcription of conversational telephone speech

This paper discusses the Cambridge University HTK (CU-HTK) system for the automatic transcription of conversational telephone speech. A detailed discussion of the most important techniques in front-end processing, acoustic modeling and model training, language and pronunciation modeling are presented. These include the use of conversation side based cepstral normalization, vocal tract length normalization, heteroscedastic linear discriminant analysis for feature projection, minimum phone error training and speaker adaptive training, lattice-based model adaptation, confusion network based decoding and confidence score estimation, pronunciation selection, language model interpolation, and class based language models. The transcription system developed for participation in the 2002 NIST Rich Transcription evaluations of English conversational telephone speech data is presented in detail. In this evaluation the CU-HTK system gave an overall word error rate of 23.9%, which was the best performance by a statistically significant margin. Further details on the derivation of faster systems with moderate performance degradation are discussed in the context of the 2002 CU-HTK 10 /spl times/ RT conversational speech transcription system.

Corrections to “Automatic Transcription of Conversational Telephone Speech”

Manuscript received December 9, 2003; August 9, 2004. This work was supported by GCHQ and by DARPA under Grant MDA972–02–0013. This paper does not necessarily reflect the position or the policy of the U.S. Government and no official endorsement should be inferred. The associate editor coordinating the review of this manuscript and approving it for publication was Dr. Geoffrey Zweig. The authors are with the Cambridge University Engineering Department, Cambridge CB2 1PZ, U.K. (e-mail: pcw@eng.cam.ac.uk). Digital Object Identifier 10.1109/TASL.2006.871051