傳統應用單回聲隱藏的浮水印技術擁有相當多的優點，但仍有一些缺點，如解碼的保密性不夠、無法承受多重編碼等。本文提出以衰減式pseudo-noise（PN）序列來模擬真實環境的回聲，並以此為嵌入音訊浮水印的基礎，PN序列的每個回聲依照其模擬返回的順序，振幅越來越小，因此在聽覺上幾乎無法感覺到以此嵌入之浮水印的存在，但根據我們的實驗結果，在解碼效能上卻不遜於傳統時域展延法。強健度的實驗比較與浮水印透明度的分析，都在本文後段的實驗結果。

Conventional watermarking techniques based on single echo hiding provide many benefits, but also have several disadvantages, for example, a lenient decoding process, weakness against multiple encoding attacks, etc. In this work, we propose an exponential decay time-spread echo as an alternative to the time-spread echo method in conventional echo hiding. Spreading an echo in the time domain is achieved by using pseudo-noise (PN) sequences with exponential decay. By exponential-decay spreading the echo, the amplitude of each echo can be reduced, i.e., the energy of each echo becomes smaller with the increase of its offset in the time domain, so that the distortion induced by watermarking is imperceptible to humans while the decoding performance of the embedded watermarks is better maintained as compared with the case of conventional time-spread echo hiding, as shown by computer simulations, in which several parameters, such as the maximum amplitude and decay constant, were varied. Robustness against typical signal processing was also evaluated in these simulations and showed fair performance. Results of a transparency SNR using some pieces of music showed good imperceptibility.

[1]. W. Bender, D. Gruhl, and N. Morimoto, “Techniques for Data Hiding,” IBM System Journal, Vol. 35, 1996, pp. 313-336.
[2]. Mitchell D. Swanson, Mei Kobayashi, and Ahmed H. Tewfik, “Multimedia Data-Embedding and Watermarking Technologies,” Proceedings of the IEEE, Vol. 86, No.6, June 1998, pp1064-1087.
[3]. Byeong-Seob Ko, Ryouichi Nishmura, Yôiti Suzuki, “Time-Spread Echo Method for Digital Audio Watermarking,” IEEE Transaction on Multimedia, Vol.7, No.2, April 2005, pp212-221.
[4]. P. Bassia, I. Pitas, and N. Nikolaidis, “Robust Audio Watermarking in the Time Domain,” IEEE Transactions on multimedia, Vol. 3, Jun 2001, pp. 232-241.
[5]. A. N. Lemma, J. Aprea, W. Oomen, and L. van de Kerkhof, “A Temporal Domain Audio Watermarking Technique,” IEEE Transactions on Signal Processing, Vol. 51, Apr 2003, pp. 1088-1097.
[6]. Ye Wang, “A New Watermarking Method of Digital Audio Content for Copyright Protection,” Signal Processing Proceedings of ICSP '98, Vol. 2, 1998, pp. 1420-1423.
[7]. Xin Li, and H. H. Yu, “Transparent and Robust Audio Data Hiding in Subband Domain,” International Conference on Information Technology: Coding and Computing, 2000.
[8]. Sang-Kwang Lee and Yo -Sung Ho, “Digital Audio Watermarking in the Cepstrum Domain,” IEEE Transactions on Consumer Electronics, Vol. 46, Aug 2000, pp.744-750.
[9]. L. Boney, A. H. Tewfik and K. N. Hamdy, “Digital Watermarking for Audio Signals,” Processings of MULTIMEDIA '96, IEEE, 1996, pp. 473-480.
[10]. M. D. Swanson, B. Zhu, A. H. Tewfik and L. Boney, “Robust audio watermarking using perceptual masking,” Signal Processing, Vol. 66, Nov 1997, pp. 337-355.
[11]. D. Gruhl, A. Lu, and W. Bender, “Echo Hiding,” Information Hiding: First International Workshop, Cambridge, U.K., May 1996, pp. 295-315.
[12]. 吳蕙如, “以回聲資訊隱藏為基礎的音訊浮水印技術設計,” 國立交通大學資訊工程研究所碩士論文, 2001.
[13]. C. Neubauer, and J. Herre, “Digital Watermarking and its Influence on Audio Quality,” AES.
[14]. I. J. Cox, J. Kilian, F. T. Leighton, and T. Shamoon, “Secure spread spectrum watermarking for multimedia,” IEEE Transactions on Image Processing, Vol. 6, Dec 1997, pp. 1673-1687.
[15]. Stefan Katzenbeisser, Fabien A. P. Petitcolas, Information Hiding Techniques for Steganography and Digital Watermarking, Artech House, United States of America, 2000
[16]. 王小川, “語音訊號處理,” 全華科技圖書, 2003.
[17]. Byeong-Seob Ko, Ryouichi Nishmura, Yôiti Suzuki, “Time-spread echo method for digital audio watermarking using PN sequences,” Proc. ICASSP 2002, May 2002.
[18]. D. Gruhl and W. Bender, “Echo hiding,” in Proc. Information Hiding Workshop, Cambridge, U.K., 1996, pp. 295–315.
[19]. A. V. Oppenheim and R. W. Schaffer, Discrete-Time Signal Processing. Englewood Cliffs, NJ: Prentice-Hall, 1989.
[20]. S. Furui, Digital Speech Processing, Synthesis, and Recognition. New York: Marcel Dekker, 1992.
[21]. Handbooks of Perception and Human Performance, vol. I, K. R. Boff, L. Kaufman, and J. D. Thomas, Eds., Wiley, New York, 1986.
[22]. Oh, H.-O., Hyun Wook Kim, Jong Won Seok, Jin Woo Hong, Dae Hee Youn, “Transparent and robust audio watermarking with a new echo embedding technique,” Multimedia and Expo, ICME 2001. IEEE International Conference on 22-25 Aug, 2001 Page(s):317 – 320.