14. The method according to claim 1 , further comprises extracting fundamental frequency information comprised in the first digital signal and determining that that the first speech signal is issued by more than one user simultaneously if the first digital signal comprises more than one fundamental frequencies.
14. The method according to claim 1 , further comprises extracting fundamental frequency information comprised in the first digital signal and determining that that the first speech signal is issued by more than one user simultaneously if the first digital signal comprises more than one fundamental frequencies. 15. The method according to claim 14 , wherein performing signal filtering on the first digital signal so as to obtain at least a first sub signal corresponding to a first user and a second sub signal corresponding to a second user from the filtered first digital signal comprises: separating the first sub signal corresponding to a first fundamental frequency of said more than fundamental frequencies from the first digital signal and separate the second sub signal corresponding to a second fundamental frequency of said more than fundamental frequencies from the first digital signal.