1. A computer-implemented method comprising: receiving, by a keyword detection system that is trained to determine whether any of multiple keywords are included in an utterance by comparing audio frame vectors of the utterance with expected event vectors for each of the keywords, a plurality of audio frame vectors that each model an audio waveform during a different period of time; generating an output feature vector for each of the audio frame vectors, wherein each output feature vector includes a set of scores that characterize an acoustic match between the corresponding audio frame vector and a set of expected event vectors and a sum of each of the scores in the set of scores for the output feature vector is one, each of the expected event vectors corresponding to one of the scores and defining acoustic properties of at least a portion of a keyword included in the multiple keywords; and providing each of the output feature vectors to a posterior handling module.