Frame-synchronized blind speech watermarking via improved adaptive mean modulation and perceptual-based additive modulation in DWT domain

Abstract

This paper presents a blind speech watermarking algorithm that adopts different strategies to embed synchronization codes and information bits into separate DWT subbands. Speech frames for data hiding are chosen based on intensity thresholding. Under the guidance of the source-filter theory, a bipolar synchronization code sequence is substituted for the noisy part of the inverse filtered excitation in the 2nd level detail subband. Such a design allows the increase of embedding strength without adversely disturbing the pitch harmonics of voiced speech. Experiment results show that a synchronization code of size 640 is sufficient to render reliable detection. The PESQ metrics indicate that the quality degradation due to the synchronization code embedding is almost negligible. As for the binary embedding in the 2nd level approximation subband, we improve the adaptive mean modulation scheme to secure the retrieval of watermark bits on a frame basis. Experiment results confirm that, with the payload capacity set at 200 bit per second (bps), the proposed scheme demonstrates better robustness than three other DWT-based methods in the presence of commonly encountered signal processing attacks. Furthermore, reducing the capacity down to 100 bps alters the low-frequency spectral distribution, which contributes noteworthy improvements in robustness and imperceptibility.