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Language Modeling for Automatic Speech Recognition Meets the Web: Google Search by Voice

Johan Schalkwyk
Boulos Harb
Peng Xu
Thorsten Brants
Vida Ha
Will Neveitt
OGI/OHSU Seminar Series, Portland, Oregon, USA (2011)


The talk presents key aspects faced when building language models (LM) for the google.com query stream, and their use for automatic speech recognition (ASR). Distributed LM tools enable us to handle a huge amount of data, and experiment with LMs that are two orders of magnitude larger than usual. An empirical exploration of the problem led us to re-discovering a less known interaction between Kneser-Ney smoothing and entropy pruning, possible non-stationarity of the query stream, as well as strong dependence on various English locales---USA, Britain and Australia. LM compression techniques allowed us to use one billion n-gram LMs in the first pass of an ASR system built on FST technology, and evaluate empirically whether a two-pass system architecture has any losses over one pass.

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