The LIMSI SDR System for TREC-9

In this paper we describe the LIMSI Spoken Document Retrieval system used in the TREC-9 evaluation. This system combines an adapted version of the LIMSI 1999 Hub-4E transcription system for speech recognition with text-based IR methods. Compared with the LIMSI TREC-8 system, this year’s system is able to index the audio data without knowledge of the story boundaries using a double windowing approach. The query expansion procedure of the information retrieval component has been revised and makes use of contemporaneous text sources. Experimental results are reported in terms of mean average precision for both the TREC SDR’99 and SDR’00 queries using the same 557h data set. The mean average precision of this year’s system is 0.5250 for SDR’99 and 0.3706 for SDR’00 for the focus unknown story boundary condition with a 20% word error rate.