TR available: Phoneme recognition with recurrent networks

[Tony Robinson]

***Do not forward to other bboards***

I've recently completed a technical report on connectionist phoneme
recognition which I would like to make available to interested researchers.
It describes a series of changes which have been made to tidy up a previously
published system.  Copies of the technical report may be obtained courtesy of
Jordan Pollack by anonymous ftp from archive.cis.ohio-state.edu in the
directory /pub/neuroprose as file robinson-tr82.ps.Z.  If this option is not
available to you, or if you would like a reprint of the background article,
please send me email giving your full address.

Tony [Robinson]

Cambridge University Engineering Department, Trumpington Street, Cambridge, UK
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	Several Improvements to a Recurrent Error Propagation Network
			  Phone Recognition System
				      
				Tony Robinson
			      ajr at eng.cam.ac.uk
			     CUED/F-INFENG/TR.82
			      30 September 1991

Recurrent Error Propagation Networks have been shown to give good performance
on the speaker independent phone recognition task in comparison with other
methods [Robinson and Fallside, Computer Speech and Language, July 1991].
This short report describes several recent improvements made to the existing
recogniser for the TIMIT database.

The improvements are: an addition to the preprocessor to represent voicing
information; use of histogram normalisation on the input channels of the
network; normalisation of the output channels to enforce unity sum; a change
in the cost function to give equal weighting to each target symbol; a change
in the representation of the outputs to reduce quantisation errors;
retraining on the complete TIMIT training set; and the better estimation of
HMM phone models.

Most of these changes decrease the number of arbitrary parameters used and
allow for the integration of the system with standard HMM techniques.  The
result of these changes is a decrease in the number of errors by about 16%
(from 36.5% to 30.7% when all 61 TIMIT phones are used and from 30.2% to
25.0% on a reduced 39 phone set).