16. A non-transitory computer-readable storage media storing instructions which, when executed by a computing device, cause the computing device 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.
19. The non-transitory computer-readable storage media of claim 16 , wherein the concatenation cost database is generated using statistical techniques which predict which of the acoustic unit sequential pairs are most likely to occur in common speech.