"The ISL RT-03 Switchboard System"
Florian Metze

This talk describes the ISL large vocabulary conversational telephony
speech  recognition  system,  which  was   tested   in NIST's   RT-03
Switchboard evaluation.  We present our experiments on improving
preprocessing, acoustic  modelling, and language modelling. The system
features  phone   dependent   semi-tied  full  covariances,  semi-tied
clustering of septa-phones, clustering across phones, feature adaptive
training, robust estimation  of  VTLN and MLLR,   as well as   context
dependent  interpolation  of  language models.    We  present detailed
results for each stage of our multi-pass transcription scheme.  System
development started in 2002 with an word error rate of 35.1% on our
internal 1h development set.   The final system performed at 21.8%,
a 38%  relative   improvement. The error rate    on the  RT-03  CTS
evaluation set is 23.4%.