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We describe a digital watermarking method for use in audio, image, video and multimedia data. We argue that a watermark must be placed in perceptually significant components of a signal if it is to be robust to common signal distortions and malicious attack. However, it is well known that modification of these components can lead to perceptual degradation of the signal. To avoid this, we propose to insert a watermark into the spectral components of the data using techniques analogous to spread sprectrum communications, hiding a narrow band signal in a wideband channel that is the data. The watermark is difficult for an attacker to remove, even when several individuals conspire together with independently watermarked copies of the data. It is also robust to common signal and geometric distortions such as digital-to-analog and analog-to-digital conversion, resampling, quantization, dithering, compression, rotation, translation, cropping and scaling. The same digital watermarking algorithm can be applied to all three media under consideration with only minor modifications, making it especially appropriate for multimedia products. Retrieval of the watermark unambiguously identifies the owner, and the watermark can be constructed to make counterfeiting almost impossible. We present experimental results to support these claims. A longer version of this document is available at: http://www.neci.nj.nec.com/tr/neci-tr-95-10.ps.

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This paper describes a coordinated experiment involving a number of UK centers, with the aim of comparing a range of systems which measure cavitational activity. Sensors have been designed at a number of universities to produce quantitative outputs based on sonochemical (Bath and Southampton), calorimetric (Coventry), electrochemical and luminescent (Southampton) measures. In addition, acoustic sensors have been produced (Guys and St. Thomas Hospital Trust, and the National Physical Laboratory). These are all deployed to monitor controlled cavitation events, ranging from single bubble phenomena to a reference cavitation bath (produced by NPL). Design of these cavitation systems has involved not only the characterization of the sound field and the vessel, but also the specification of some reference cavitation liquid (NPL and Southampton). Comparison of the resulting measures of activity allows the feasibility of a scale for cavitation to be investigated.

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