6. The speech synthesis method of claim 5 , wherein the first group of speech segments is represented by a first statistical model and the second group of speech segments is represented by a second statistical model, and wherein calculating the value comprises: using the transformation to transform the second statistical model to obtain a transformed statistical model; and calculating the value as a distance between the transformed second statistical model and the first statistical model.
6. The speech synthesis method of claim 5 , wherein the first group of speech segments is represented by a first statistical model and the second group of speech segments is represented by a second statistical model, and wherein calculating the value comprises: using the transformation to transform the second statistical model to obtain a transformed statistical model; and calculating the value as a distance between the transformed second statistical model and the first statistical model. 7. The speech synthesis method of claim 6 , wherein the distance between the transformed second statistical model and the first statistical model is a Kullback-Liebler divergence between the transformed second statistical model and the first statistical model.