20. A first speech synthesis system according to claim 19 , wherein the speech segment selector is adapted to imitate the unit selection behavior of a second more complex speech synthesis system based on at least one of a richer feature set and more complex cost functions, by integrating into the compound speech unit database of the first synthesis system data derived from the output of the second more complex speech synthesis system.
20. A first speech synthesis system according to claim 19 , wherein the speech segment selector is adapted to imitate the unit selection behavior of a second more complex speech synthesis system based on at least one of a richer feature set and more complex cost functions, by integrating into the compound speech unit database of the first synthesis system data derived from the output of the second more complex speech synthesis system. 21. A speech synthesis system according to claim 20 , wherein the compound speech unit database includes linguistic feature vectors from compound speech units derived from synthesized speech validated by an algorithm of perceptual measures.