1. A method comprising: providing a set of subword unit models; for each of two acoustic events, a first acoustic event occurring in a first acoustic signal and a second acoustic event occurring in a second acoustic signal, and for each of a series of times in each of the events, computing a probability associated with each model of the set of subword unit models; and computing a quantity characterizing a comparison of the two acoustic events using the computed probabilities.
6. The method of claim 1 wherein computing the probability associated with each model of the set of subword unit models includes computing a probability distribution over a set of subword units corresponding with the set of subword unit models.