17. The non-transitory computer-readable storage medium of claim 15 , the instructions which, when executed by the computing device, cause the computing device to perform a method further comprising: combining the first speech signal and the second speech signal to form a mixed signal; and adding the mixed signal to the database of reference signals.
15. A non-transitory computer-readable storage medium having stored therein instructions which, when executed by a computing device, cause the computing device 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.