Improved automatic speech recognition through speaker normalization

  • Authors:
  • Diego Giuliani;Matteo Gerosa;Fabio Brugnara

  • Affiliations:
  • ITC-irst, Centro per la Ricerca Scientifica e Tecnologica, Via Sommarive, 18, I-38050 Povo, Trento, Italy;ITC-irst, Centro per la Ricerca Scientifica e Tecnologica, Via Sommarive, 18, I-38050 Povo, Trento, Italy and University of Trento, International Graduate School I-38050 Povo, Trento, Italy;ITC-irst, Centro per la Ricerca Scientifica e Tecnologica, Via Sommarive, 18, I-38050 Povo, Trento, Italy

  • Venue:
  • Computer Speech and Language
  • Year:
  • 2006

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Abstract

In this paper, speaker adaptive acoustic modeling is investigated by using a novel method for speaker normalization and a well known vocal tract length normalization method. With the novel normalization method, acoustic observations of training and testing speakers are mapped into a normalized acoustic space through speaker-specific transformations with the aim of reducing inter-speaker acoustic variability. For each speaker, an affine transformation is estimated with the goal of reducing the mismatch between the acoustic data of the speaker and a set of target hidden Markov models. This transformation is estimated through constrained maximum likelihood linear regression and then applied to map the acoustic observations of the speaker into the normalized acoustic space. Recognition experiments made use of two corpora, the first one consisting of adults' speech, the second one consisting of children's speech. Performing training and recognition with normalized data resulted in a consistent reduction of the word error rate with respect to the baseline systems trained on unnormalized data. In addition, the novel method always performed better than the reference vocal tract length normalization method adopted in this work. When unsupervised static speaker adaptation was applied in combination with each of the two speaker normalization methods, a different behavior was observed on the two corpora: in one case performance became very similar while in the other case the difference remained significant.