12. The system of claim 9 , wherein the concatenation cost database contains a portion of all possible concatenation costs.
9. A system comprising: a processor; and a computer readable storage medium storing instructions for controlling the processor to perform steps comprising: generating a concatenation cost database by synthesizing, via a processor, a body of speech and identifying acoustic unit sequential pairs in the body of speech and respective concatenation costs; determining whether an acoustic unit sequential pair to be used for synthesizing speech has a concatenation cost in the concatenation cost database; and if the concatenation cost database does not contain the concatenation cost for the acoustic unit sequential pair, calculating an actual concatenation cost for the acoustic unit sequential pair.