A method and apparatus is disclosed herein for a quantizing parameters using partial information on atypical subsequences. In one embodiment, the method comprises partially classifying a first plurality of subsequences in a target vector into a number of selected groups, creating a refined fidelity criterion for each subsequence of the first plurality of subsequences based on information derived from classification, dividing a target vector into a second plurality of subsequences, and encoding the second plurality of subsequences, including quantizing the second plurality of subsequences given the refined fidelity criterion.