9. A system, comprising: a buffer to store samples representing an input audio signal, a speech feature extractor having an input for samples from the buffer, a speech vocabulary storing data representing a predetermined set of speech elements, and a controller comprising a decision circuit to generate a wake up signal in response to a match between speech features output by the extractor and the stored speech elements, wherein the controller is configured to output a wake up signal indicating the match and to output samples received subsequent to the samples stored in the buffer corresponding to the match.
9. A system, comprising: a buffer to store samples representing an input audio signal, a speech feature extractor having an input for samples from the buffer, a speech vocabulary storing data representing a predetermined set of speech elements, and a controller comprising a decision circuit to generate a wake up signal in response to a match between speech features output by the extractor and the stored speech elements, wherein the controller is configured to output a wake up signal indicating the match and to output samples received subsequent to the samples stored in the buffer corresponding to the match. 25. The system of claim 9 , wherein the speech vocabulary stores data representing one or more of a target word or target phrase, and wherein the decision circuit is configured to generate the wake up signal in response to a match between speech features output by the extractor and the one or more of the target word or target phrase.