17. The non-transitory computer-readable storage media of claim 16 , further comprising if the concatenation cost database contains the concatenation cost for the acoustic unit sequential pair, synthesizing the speech using a respective concatenation cost for the speech from the concatenation cost database.
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.