16. The computer-readable storage device of claim 15 , having additional instructions stored which, when executed by the computing device, cause the computing device to perform operations comprising: mixing the speech signal with a second speech signal, to yield a mixed speech signal; and adding the mixed speech signal to the database of reference speech signals.
16. The computer-readable storage device of claim 15 , having additional instructions stored which, when executed by the computing device, cause the computing device to perform operations comprising: mixing the speech signal with a second speech signal, to yield a mixed speech signal; and adding the mixed speech signal to the database of reference speech signals. 17. The computer-readable storage device of claim 16 , wherein the speech signal and the second speech signal are received from the user.