1. A method of generating a task-dependent acoustic model from a task-independent (TI) training corpus that includes an acoustic representation of an utterance and a sequence of transcribed words corresponding to the acoustic representation, the method comprising: deriving a task relevance measure for each word in the TI training corpus, indicative of a relevance of the words to a task; training a task-independent (TI) AM based on the TI training corpus, the TI AM including words from the TI training corpus and associated AM parameters; and generating a task-dependent (TD) acoustic model (AM) based on the TI AM trained from the TI training corpus and the task relevance measures for the words in the TI training corpus.