Using F0 to constrain the unit selection Viterbi network

The goal of the work described here is to limit the computation needed in unit selection Viterbi search for text-to-speech synthesis. The broader goal is to improve speech quality through the practical use of significantly larger databases. We focus in this paper on trying to reduce the number of concatenation cost calculations. By making certain weak assumptions about f₀ distributions we estimate that only a fraction of possible concatenations are relevant. A method for selecting the relevant concatenations by imposing an ordering constraint on candidate units is proposed. The ordering is based on unit f₀ value(s). Strengths and weaknesses of this approach are discussed and data is presented about calculation complexity compared with naive Viterbi search. A listening test was conducted to investigate the effect on synthesis quality under various configurations of algorithm and database.