1. A computer-readable storage medium having computer-executable instructions stored thereon that when executed by a computer cause the computer to perform steps comprising: generating a set of syllable-like units using mutual information before decoding a speech signal to identify a sequence of syllable-like units; generating a speech-based phonetic description of a word without reference to the text of the word by decoding a speech signal representing the user's pronunciation of the word to generate the speech-based phonetic description of the word, wherein decoding a speech signal comprises identifying a sequence of syllable-like units from the speech signal; generating a text-based phonetic description of the word based on the text of the word; aligning the speech-based phonetic description and the text-based phonetic description on a phone-by-phone basis to form a single graph; and selecting a phonetic description from the single graph.