1. A speech recognition circuit, comprising: an audio front end for calculating a feature vector from an audio signal, wherein the feature vector comprises a plurality of extracted and/or derived quantities from said audio signal during a defined audio time frame; a calculating circuit for calculating distances indicating the similarity between a feature vector and a plurality of predetermined acoustic states of an acoustic model; and a search stage for using said calculated distances to identify words within a lexical tree, the lexical tree comprising a model of words; wherein said audio front end and said search stage are implemented using a first processor, and said calculating circuit is implemented using a second processor, and wherein data is pipelined from the front end to the calculating circuit to the search stage.