Hybrid Speech Watermarking Based on Formant Enhancement and Cochlear Delay

Illegal use of digital technologies has brought a series of problems in speech protection and authorization. Digital watermarking can effectively solve these problems by embedding watermarks into the host signals. This paper proposes a hybrid watermarking method for speech signals based on the concepts of formant enhancement (FE) and cochlear delay (CD). This hybrid method utilizes the source-filter model of speech production to separate the speech into vocal tract filter (characterized by formants) and the sound source (excitation signal/residue) so that the FE-based watermarking and CD-based watermarking can be separately applied. Objective evaluations related to inaudibility and robustness were carried out to evaluate the proposed method. The results showed that the proposed method could satisfy inaudibility, and the robustness could be increased in comparison with single method by taking advantages of both two methods. These results also verified the effectiveness of the proposed method.