8. A system comprising: a processor; and a non-transitory computer-readable storage medium having stored therein instructions which, when executed by the processor, cause the processor to perform a method comprising: receiving a first speech signal and a second speech signal; generating feature coefficients based at least in part on the first speech signal and the second speech signal; comparing the feature coefficients to a codebook to yield an utterance similarity value, wherein the codebook is associated with a database of reference speech signals; if the utterance similarity value is above a threshold, providing access to a service and adding at least one of the first speech signal and the second speech signal to the database of reference signals.
8. A system comprising: a processor; and a non-transitory computer-readable storage medium having stored therein instructions which, when executed by the processor, cause the processor to perform a method comprising: receiving a first speech signal and a second speech signal; generating feature coefficients based at least in part on the first speech signal and the second speech signal; comparing the feature coefficients to a codebook to yield an utterance similarity value, wherein the codebook is associated with a database of reference speech signals; if the utterance similarity value is above a threshold, providing access to a service and adding at least one of the first speech signal and the second speech signal to the database of reference signals. 11. The system of claim 8 , wherein the feature coefficients are at least one of cepstrum coefficients and linear predictive coding coefficients.