1. A method of classifying input data representing speech input by a user of a speech application as belonging to one of a plurality of classifications, the plurality of classifications associated with a respective plurality of clusters that were fit to training data representing a plurality of speech utterances associated with the speech application, the method comprising: using at least one processor to perform: obtaining a first transformation generated using only a subset of the training data based, at least in part, on frequency information corresponding to a number of times respective words in a vocabulary of interest occurred in the subset of the training data, wherein the plurality of clusters were fit to the training data at least in part by fitting the plurality of clusters to transformed training data obtained by applying the first transformation to the training data; transforming the input data using at least the first transformation to obtain transformed input data representing speech input by the user of the speech application; comparing the transformed input data to the plurality of clusters to determine which cluster of the plurality of clusters the input data should be associated with; and classifying the input data according to a classification of the plurality of classifications associated with the cluster that the input data was determined to be associated with.