1. A method comprising: generating, via a processor, a feature coefficient based on a speech signal from a user; comparing the feature coefficient to a user-specific codebook associated with the user, to yield a similarity value, wherein the user-specific codebook utilizes utterances from both the user and a group of non-users; and when the similarity value meets a threshold: adding the speech signal to a database of reference speech signals associated with the user-specific codebook; and adding the feature coefficient to the user-specific codebook.
1. A method comprising: generating, via a processor, a feature coefficient based on a speech signal from a user; comparing the feature coefficient to a user-specific codebook associated with the user, to yield a similarity value, wherein the user-specific codebook utilizes utterances from both the user and a group of non-users; and when the similarity value meets a threshold: adding the speech signal to a database of reference speech signals associated with the user-specific codebook; and adding the feature coefficient to the user-specific codebook. 5. The method of claim 1 , wherein the threshold is determined using a Chi-squared detector.