11. A system comprising: a cluster determining unit for determining the cluster for the unit to be subjected to text-to-speech conversion to determine the Gaussian Mixture Model of the cluster, wherein the Gaussian Mixture Model is generated from samples clustered through the use of a decision tree which includes combining two branches in the decision tree for clustering samples if the two branches are similar for further clustering; a distance calculating unit; using electronic logic circuitry for calculating the distance between the candidate samples in the cluster and the determined Gaussian Mixture Model; and an optimizing unit, for identifying the sample with the smallest distance for subsequent speech synthesizing.
18. The system according to claim 11 , wherein the calculating unit further comprises: means for obtaining descriptive prosody annotation information of each unit to be subjected to text-to-speech conversion; means for finding the context equivalent cluster of each unit to be subjected to text-to-speech conversion, which corresponds to a mixture model; means for evaluating all the candidates of the unit to be text-to-speech conversion synthesized through the Gaussian Mixture Model-based distance definition; and wherein the optimizing unit further comprises means for finding the overall optimal candidate series, for subsequent speech synthesizing, based on the distance from the means for evaluating and criteria of overall optimization.