Time conditioned search in automatic speech recognition reconsidered

In this paper we re-investigate the time conditioned search (TCS) method in comparison to the well known word conditioned search (WCS), and analyze its applicability on state-ofthe-art large vocabulary continuous speech recognition tasks. In contrast to current standard approaches, time conditioned search offers theoretical advantages particularly in combination with huge vocabularies and huge language models, but it is difficult to combine with across word modelling, which was proven to be an important technique in automatic speech recognition. Our novel contributions for TCS are a pruning step during the recombination called Early Word End Pruning, an additional recombination technique called Context Recombination, the idea of a Startup Interval to reduce the number of started trees, and a mechanism to combine TCS with across word modelling. We show that, with these techniques, TCS can outperform WCS on current ASR tasks.