Modeling state durations in hidden Markov models for automatic speech recognition

  • Authors:
  • Padma Ramesh;Jay G. Wilpon

  • Affiliations:
  • Speech Research Department, AT&T Bell Laboratories, Murray Hill, NJ;Speech Research Department, AT&T Bell Laboratories, Murray Hill, NJ

  • Venue:
  • ICASSP'92 Proceedings of the 1992 IEEE international conference on Acoustics, speech and signal processing - Volume 1
  • Year:
  • 1992

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Abstract

Hidden Markov modeling (HMM) techniques have been used successfully for connected speech recognition in the last several years. In the traditional HMM algorithms the probability of duration of a state decreases exponentially with time which is not appropriate for representing the temporal structure of speech. Non-parametric modeling of duration using semi-Markov chains does accomplish the task with a large increase in the computational complexity. Applying a post processing state duration penalty after Viterbi decoding adds very little computation but does not affect the forward recognition path. In this paper we present a way of modeling state durations in HMM using time dependent state transitions. This new inhomogeneous HMM (IHMM) does increase the computation by a small amount but reduces recognition error rates by 14-25%. Also, a suboptimal implementation of this scheme that requires no more computation than the traditional HMM is presented which also has reduced errors by 14-22% on a variety of databases.