Ryuki Tachibana, Shuichi Shimizu, Taiga Nakamura, Seiji Kobayashi, "An Audio Watermarking Method Robust against Time- and Frequency-Fluctuation", Proceedings of Security and Watermarking of Multimedia Contents III, SPIE vol. 4314, pp. 104-115, San Jose, USA, January 2001.
Abstract: In this paper, we describe an audio watermarking algorithm that can embed a multiple-bit message which is robust against wow-and-flutter, cropping, noise-addition, pitch-shift, and audio compressions such as MP3. The embedding algorithm calculates and manipulates the magnitudes of segmented areas in the time-frequency plane of the content using short-term DFTs. The detection algorithm correlates the magnitudes with a pseudo-random array that corresponds to two-dimensional areas in the time-frequency plane. The two-dimensional array makes the watermark robust because, even when some portions of the content are heavily degraded, other portions of the content can match the pseudo-random array and contribute to watermark detection. Another key idea is manipulation of magnitudes. Because magnitudes are less influenced than phases by fluctuations of the analysis windows caused by
random cropping, the watermark resists degradation. When signal transformation causes pitch fluctuations in the content, the frequencies of the pseudo-random array embedded in the content shift, and that causes a decrease in the volume of the watermark signal that still correctly overlaps with the corresponding pseudo-random array. To keep the overlapping area wide enough for successful watermark detection, the widths of the frequency subbands used for the detection segments should be increased as frequency increases. We theoretically and experimentally analyze the robustness of proposed algorithm against a variety of signal degradations.
http://www.trl.ibm.com/projects/RightsManagement/datahiding/paper/Ryuki_EI01Paper.pdf