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An approach to watermarking digital signals using frequency modulation - ‘Chirp Coding’ - is considered. The principles underlying this approach are based on the use of a matched filter to reconstruct a ‘chirp stream’ code that is uniquely robust. The method is generic in the sense that it can, in principle, be used for a variety of different signal (the authentication of speech and biomedical signals, for example). Further, by generating a bit stream that is signal dependent, chirp coding provides a method of self-authentication, which has a wide range of applications including copyright protection and digital rights management. However, in this paper, we focus on the application of chirp coding for the verification, authentication and self-authentication of audio signals. We also consider the effect of using a multi-level chirp coding approach to increase the ‘volume’ of data that can be embedded into a host signal.
The theoretical and computational aspects of the matched filter with regard to the properties of a chirp are briefly revisited to provide the essential background to the method. Coding and decoding methods are then addressed and the results of different ‘attack strategies’ considered including Objective Difference Grades that are evaluated using Perceptual Evaluation of Audio Quality
Blackledge, J., Farooq, O.: Audio Data Verification and Authentication using Frequency Modulation based Watermarking. International Society for Advanced Science and Technology, Journal of Electronics and Signal Processing. Vol. 3 (ISSN 1797-2329), issue: No 2, pages: 51 - 63, 2008. doi:10.21427/D7G90N