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Generating Exact Lattices in the WFST Framework

Daniel Povey, Mirko Hannemann, Gilles Boulianne, Lukas Burget, Arnab Ghoshal, Milos Janda, Martin Karafiat, Stefan Kombrink, Petr Motlıcek, Yanmin Qian, Korbinian Riedhammer, Karel Vesely, and Ngoc Thang Vu


We describe a lattice generation method that is exact, i.e. it satisfies all the natural properties we would want from a lattice of alternative transcriptions of an utterance. This method does not introduce substantial overhead above one-best decoding. Our method is most directly applicable when using WFST decoders where the WFST is “fully expanded”, i.e. where the arcs correspond to HMM transitions. It outputs lattices that include HMM-state-level alignments as well as word labels. The general idea is to create a state-level lattice during decoding, and to do a special form of determinization that retains only the best-scoring path for each word sequence. This special determinization algorithm is a solution to the following problem: Given a WFST A, compute a WFST B that, for each input-symbol sequence of A, contains just the lowest-cost path through A.


Publication typeInproceedings
PublisherIEEE International Confrence on Acoustics, Speech, and Signal Processing (ICASSP)
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