Audio watermarking: a way to stationnarize audio signals

Audio watermarking is usually used as a multimedia copyright protection tool or as a system that embed metadata in audio signals. In this paper, watermarking is viewed as a preprocessing step for further audio processing systems: the watermark signal conveys no information, rather it is used to modify the statistical characteristics of an audio signal, in particular its nonstationarity. The embedded watermark is then added in order to stationnarize the host signal. Indeed, the embedded watermark is piecewise stationary, thus it modifies the stationarity of the original audio signal. In some audio processing fields, this fact can be used to improve performances that are very sensitive to time-variant signal statistics. This work presents an analysis of the perceptual watermarking impact on the stationarity of audio signals. The study is based on stationarity indices, which represent a measure of variations in spectral characteristics of signals, using time-frequency representations. Simulation results with two kinds of signals, artificial signals and audio signals (speech and music), are presented. Stationarity indices comparison between watermarked and original audio signals shows a significant stationarity enhancement of the watermarked signal, especially for transient attacks.