Re-synchronizing audio watermarking after non-linear time stretching

Digital audio watermarking today is robust to many common attacks, including lossy compression and digital-to-analogue conversion. One robustness and security challenge, still, is time-stretching. This operation speeds up or slows down the playback speed while preserving the tone pitch. Although inaudible for an uninformed listener if smoothly applied, time-stretching can be confusing for a blind watermark detection algorithm. We introduce a non-blind approach for reconstructing the original timing based on dynamic time warping. Our experiments show that the approach is successful even if non-linear stretching was applied. Our solution can significantly increase the robustness and security of every audio watermarking scheme that is dependent on precise timing conditions at detection time.