Admissible Stopping in Viterbi Beam Search for Unit Selection Speech Synthesis

Shinsuke SAKAI  Tatsuya KAWAHARA  

IEICE TRANSACTIONS on Information and Systems   Vol.E96-D   No.6   pp.1359-1367
Publication Date: 2013/06/01
Online ISSN: 1745-1361
DOI: 10.1587/transinf.E96.D.1359
Print ISSN: 0916-8532
Type of Manuscript: PAPER
Category: Speech and Hearing
speech synthesis,  unit selection,  concatenation cost,  Viterbi search,  

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Corpus-based concatenative speech synthesis has been widely investigated and deployed in recent years since it provides a highly natural synthesized speech quality. The amount of computation required in the run time, however, can often be quite large. In this paper, we propose early stopping schemes for Viterbi beam search in the unit selection, with which we can stop early in the local Viterbi minimization for each unit as well as in the exploration of candidate units for a given target. It takes advantage of the fact that the space of the acoustic parameters of the database units is fixed and certain lower bounds of the concatenation costs can be precomputed. The proposed method for early stopping is admissible in that it does not change the result of the Viterbi beam search. Experiments using probability-based concatenation costs as well as distance-based costs show that the proposed methods of admissible stopping effectively reduce the amount of computation required in the Viterbi beam search while keeping its result unchanged. Furthermore, the reduction effect of computation turned out to be much larger if the available lower bound for concatenation costs is tighter.