

Department of Engineering  
University of Cambridge > Engineering Department > Machine Intelligence Lab 
MAXIMUM LIKELIHOOD LINEAR TRANSFORMATIONS FOR HMMBASED SPEECH RECOGNITION
M.J.F. Gales
May 1997
This paper examines the application of linear transformations for speaker and environmental adaptation in an HMMbased speech recognition system. In particular, transformations that are trained in a maximum likelihood sense on adaptation data are investigated. Other than in the form of a simple bias, strict linear featurespace transformations are inappropriate in this case. Hence, only modelbased linear transforms are considered. The paper compares the two possible forms of modelbased transforms: (i) unconstrained, where any combination of mean and variance transform may be used, and (ii) constrained, which requires the variance transform to have the same form as the mean transform (sometimes referred to as featurespace transforms). Reestimation formulae for all appropriate cases of transform are given. This includes a new and efficient ``full'' variance transform and the extension of the constrained modelspace transform from the simple diagonal case to the full or blockdiagonal case. The constrained and unconstrained transforms are evaluated in terms of computational cost, recognition time efficiency, and use for speaker adaptive training. The recognition performance of the two modelspace transforms on a large vocabulary speech recognition task using incremental adaptation is investigated. In addition, initial experiments using the constrained modelspace transform for speaker adaptive training are detailed.
If you have difficulty viewing files that end '.gz'
,
which are gzip compressed, then you may be able to find
tools to uncompress them at the gzip
web site.
If you have difficulty viewing files that are in PostScript, (ending
'.ps'
or '.ps.gz'
), then you may be able to
find tools to view them at
the gsview
web site.
We have attempted to provide automatically generated PDF copies of documents for which only PostScript versions have previously been available. These are clearly marked in the database  due to the nature of the automatic conversion process, they are likely to be badly aliased when viewed at default resolution on screen by acroread.
 Search  CUED  Cambridge University  
©
2005 Cambridge University Engineering Dept Information provided by milabmaintainer 