A Generalized Dynamic Composition Algorithm of Weighted Finite State Transducers for Large Vocabulary Speech Recognition

We propose a generalized dynamic composition algorithm of weighted finite state transducers (WFST), which avoids the creation of non-coaccessible paths, performs weight look-ahead and does not impose any constraints to the topology of the WFSTs. Experimental results on Wall Street Journal (WSJ1) 20k-word trigram task show that at 17\% WER (moderately-wide beam width), the decoding time of the proposed approach is about 48\% and 65\% of the other two dynamic composition approaches. In comparison with static composition, at the same level of 17\% WER, we observe a reduction of about 60\% in memory requirement, with an increase of about 60\% in decoding time due to extra overheads for dynamic composition

Language Model Combination and Adaptation Using Weighted Finite State Transducers

In speech recognition systems language model (LMs) are often constructed by training and combining multiple n-gram models. They can be either used to represent different genres or tasks found in diverse text sources, or capture stochastic properties of different linguistic symbol sequences, for example, syllables and words. Unsupervised LM adaption may also be used to further improve robustness to varying styles or tasks. When using these techniques, extensive software changes are often required. In this paper an alternative and more general approach based on weighted finite state transducers (WFSTs) is investigated for LM combination and adaptation. As it is entirely based on well-defined WFST operations, minimum change to decoding tools is needed. A wide range of LM combination configurations can be flexibly supported. An efficient on-the-fly WFST decoding algorithm is also proposed. Significant error rate gains of 7.3% relative were obtained on a state-of-the-art broadcast audio recognition task using a history dependently adapted multi-level LM modelling both syllable and word sequence

An algorithm for fast composition of weighted finite-state transducers

Abstract In automatic speech recognition based on weighted-finite transducers, a static decoding graph HC • L • G is typically constructed. In this work, we first show how the size of the decoding graph can be reduced and the necessity of determinizing it can be eliminated by removing the ambiguity associated with transitions to the backoff state or states in G. We then show how the static construction can be avoided entirely by performing fast on-the-fly composition of HC and L • G. We demonstrate that speech recognition based on this on-the-fly composition approximately 80% more run-time than recognition based on the statically-expanded network R, which makes it competitive compared with other dynamic expansion algorithms that have appeared in the literature. Moreover, the dynamic algorithm requires a factor of approximately seven less main memory as the recognition based on the static decoding graph

A Weighted Finite State Transducer tutorial

The concepts of WFSTs are summarised, including structural and stochastic optimisations. A typical composition process for ASR is described. Some experiments show that care should be taken with silence models

A generalized dynamic composition algorithm of weighted finite state transducers for large vocabulary speech recognition

We propose a generalized dynamic composition algorithm of weighted �nite state transducers (WFST), which avoids the creation of noncoaccessible paths, performs weight look-ahead and does not impose any constraints to the topology of the WFSTs. Experimental results on Wall Street Journal (WSJ1) 20k-word trigram task show that at 17 % WER (moderately-wide beam width), the decoding time of the proposed approach is about 48 % and 65 % of the other two dynamic composition approaches. In comparison with static composition, at the same level of 17 % WER, we observe a reduction of about 60% in memory requirement, with an increase of about 60 % in decoding time due to extra overheads for dynamic composition