Time-spread echo method for digital audio watermarking

Conventional watermarking techniques based on echo hiding provide many benefits, but also have several disadvantages, for example, a lenient decoding process, weakness against multiple encoding attacks, etc. In this paper, to improve the weak points of conventional echo hiding, we propose a time-spread echo as an alternative to the single echo in conventional echo hiding. Spreading an echo in the time domain is achieved by using pseudonoise (PN) sequences. By spreading the echo, the amplitude of each echo can be reduced, i.e., the energy of each echo becomes small, 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 echo hiding, as shown by computer simulations, in which several parameters, such as the amplitude and length of PN sequences and analysis window length, were varied. Robustness against typical signal processing was also evaluated in these simulations and showed fair performance. Results of a listening test using some pieces of music showed good imperceptibility.