9. A method of building class-specific cluster systems comprising the steps of: providing a speaker dependent system for each of a plurality of training speakers; partitioning an acoustic space according to classes, each class being characterized by a set of acoustic features; grouping the speaker dependent systems with the acoustic spaces according to classes to build acoustic spaces with common features from all the speaker dependent systems; and clustering the grouped acoustic spaces with common features to form cluster systems based on acoustic characteristics of the speakers, the acoustic characteristics including class-specific characteristics.
17. The method of building class-specific cluster systems as recited in claim 9, wherein the step of providing a speaker dependent system for each of a plurality of training speakers further comprises the steps of: decoding training data of a speaker based on a speaker-independent system; and building the speaker dependent system by storing a set of labeled acoustic vectors for the speaker.