20. A system for synthesizing a target voice, comprising: a processor; and a storage medium having program instructions written thereon for execution on the processor, the program instructions including program instructions for: a front end module configured to receive symbolic input descriptive of an utterance to be synthesized, a back end module configured to select one or more portions of the utterance to be constructed from certain Phone-and-Transition (P&T) speech units that function as prototype speech units, the prototype speech units obtained from a target voice corpus, the target voice corpus including speech units recorded from a human speaker, the target voice corpus configured to provide characteristics of the target voice, a unit engine of the back end module configured to apply adaptations to selected ones of the prototype speech units of the target voice corpus that are derived from a context different than the one in which they are to be used in the utterance, to produce adapted speech units that are contextually appropriate for the utterance, and a concatenation engine of the back end module configured to concatenate at least the adapted speech units from the target voice corpus and speech units from a source other than the target voice corpus, to produce a speech waveform for the utterance.
24. The system of claim 20 wherein the speech units of the target voice corpus are recorded from two or more different human speakers.