Language model adaptation for ASR of spoken translations using phrase-based translation models and named entity models

Language model adaptation based on Machine Translation (MT) is a recently proposed approach to improve the Automatic Speech Recognition (ASR) of spoken translations that does not suffer from a common problem in approaches based on rescoring i.e. errors made during recognition cannot be recovered by the MT system. In previous work we presented an efficient implementation for MT-based language model adaptation using a word-based translation model. By omitting renormalization and employing weighted updates, the implementation exhibited virtually no adaptation overhead, enabling its use in a real-time setting. In this paper we investigate whether we can improve recognition accuracy without sacrificing the achieved efficiency. More precisely, we investigate the effect of both state-of-the-art phrase-based translation models and named entity probability estimation. We report relative WER reductions of 6.2% over a word-based LM adaptation technique and 25.3% over an unadapted 3-gram baseline on an English-to-Dutch dataset.