1. A system for speech synthesis, the system comprising: a processor; a first module controlling the processor to receive a set of ordered lists of speech units; a second module controlling the processor, for each respective speech unit in each ordered list in the set of ordered lists, to construct a sublist of speech units from a next ordered list which are suitable for concatenation; a third module controlling the processor to perform a cost analysis of paths through the set of ordered lists of speech units based on the sublist of speech units for each respective speech unit; and a fourth module controlling the processor to synthesize speech using a lowest cost path of speech units through the set of ordered lists based on the cost analysis.