Hidden mode HMM using Bayesian network for modeling speaking rate fluctuation

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Abstract
One of the most important issues in spontaneous speech recognition is how to cope with the degradation of recog- nition accuracy due to speaking rate fluctuation within an utterance. This paper proposes an acoustic model for adjust- ingmixtureweightsandtransitionprobabilitiesoftheHMM foreachframeaccordingtothelocalspeakingrate. Thepro- posedmodelisimplementedalongwithvariantsandconven- tional models using the Bayesian network framework. The proposed model has a hidden variable representing varia- tion of the "mode" of the speaking rate and its value con- trols the parameters of the underlying HMM. Model train- ing and maximum probability assignment of the variables are conducted using the EM/GEM and inference algorithms for Bayesian networks. Utterances from meetings and lec- tures are used for evaluation where Bayesian network-based acoustic models are used to rescore the utterance hypothe- sesobtainedfromafirst-passN-bestlist. Intheexperiments, the proposed model shows consistently higher performance than conventional models.