Tied mixtures in the Lincoln robust CSR

  • Authors:
  • Douglas B. Paul

  • Affiliations:
  • Lincoln Laboratory, MIT, Lexington, MA

  • Venue:
  • HLT '89 Proceedings of the workshop on Speech and Natural Language
  • Year:
  • 1989

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Abstract

HMM recognizers using either a single Gaussian or a Gaussian mixture per state have been shown to work fairly well for 1000-word vocabulary continuous speech recognition. However, the large number of Gaussians required to cover the entire English language makes these systems unwieldy for large vocabulary tasks. Tied mixtures offer a more compact way of representing the observation pdf's. We have converted our independent mixture systems to tied mixtures and have obtained mixed results: a 13% improvement in speaker-dependent recognition without cross-word triphone models, but no improvement in our speaker-dependent system with cross-word boundary triphone models or in our speaker-independent system. There is also a reduction in CPU requirements during recognition—but this is counter-balanced by an increase during training. This paper also includes a comment on the validity of the DARPA program's evaluation test system comparisons.