18. The computer readable storage medium of claim 15, wherein step (e) further includes the steps of: (e1) determining if an amplifier gain is saturated; (e2) when the amplifier gain is saturated, going to step (a).
15. A computer readable storage medium containing computer readable instructions that when executed by a computer performs the following steps: (a) requesting a user speak a vocabulary word; (b) receiving a first digitized utterance; (c) extracting a plurality of features from the first digitized utterance; (d) determining a signal to noise ratio; (e) when the signal to noise ratio is less than a predetermined signal to noise ratio, returning to step (a); (f) requesting the user speak the vocabulary word; (g) receiving a second digitized utterance of the vocabulary word; (h) extracting the plurality of features from the second digitized utterance; (i) determining a first similarity between the plurality of features from the first digitized utterance and the plurality of features from the second digitized utterance; (j) when the first similarity is less than a predetermined similarity, requesting the user to speak a third utterance of the vocabulary word; (k) extracting the plurality of features from a third digitized utterance; (l) determining a second similarity between the plurality of features from the first digitized utterance and the plurality of features from the third digitized utterance; and (m) when the second similarity is greater than or equal to the predetermined similarity, forming a reference for the vocabulary word.