Modification of polar echo kernel for performance improvement of audio watermarking

In this paper, we present a new echo kernel , which is a modification of polar echo kernel, to improve the detection performance and robustness against attacks. Polar echo kernel may have the advantage of large detection margin from the polarity of inserted echo signal, but its poor frequency response in low frequency band degrades sound quality. To solve this problem, we applied bipolar echo pulses to the polar echo kernel. Using the proposed echo kernel, the distributions of autocepstrum peaks for data '0' and '1' are located more distant and improvement of detection performance is achieved. It also makes the low frequency band flat so that the timbre difference in the polar echo kernel can be removed to reproduce the imperceptible sound quality. Informal listening tests as well as robustness test against attacks were performed to evaluate the proposed echo kernel. Experimental results demonstrated the superiority of the proposed echo kernel to both conventional unipolar and polar echo kernels.