3. The method of claim 2 wherein each function further comprises the product of a posterior probability of a mixture component based on the training speech signal and a difference between a training mean and a background mean.
3. The method of claim 2 wherein each function further comprises the product of a posterior probability of a mixture component based on the training speech signal and a difference between a training mean and a background mean. 4. The method of claim 3 further comprising selecting training means for use in the functions based on the nominal user identification.