1. A method for classifying an audio signal containing speech information, the method comprising: receiving the audio signal; classifying a sound in the audio signal as a vowel class when a first phoneme-based model determines that the sound corresponds to a sound represented by a set of phonemes that define vowels; classifying the sound in the audio signal as a fricative class when a second phoneme-based model determines that the sound corresponds to a sound represented by a set of phonemes that define consonants; and classifying the sound in the audio signal based on at least one non-phoneme based model.