11. The method of claim 10 , further comprising: determining a respective duration score for each speech unit in an utterance including the single speech unit; and wherein the normalizing the duration score comprises multiplying the determined respective duration scores of each speech unit in the utterance together and taking an Nth root of a result of the multiplying, where N is a number of speech units in the utterance.
10. The method of claim 4 , further comprising normalizing the duration score using a number of speech units in an utterance comprising the single speech unit.