Blind Watermarking of Audio Signals by Using Phase Modifications

摘要

Watermarking of audio signals intends to manipulate the audio signal in a way that the changes in the audio content cannot be recognised by the human auditory system. In order to reduce the audibility of the watermark and to improve the robustness of the watermarking the invention uses phase modification of the audio signal. In the frequency domain, the phase of the audio signal is manipulated by the phase of a reference phase sequence, followed by transform into time domain. Because a change of the audio signal phase over the whole frequency range can be audible, the phase manipulation is carried out with a maximum amount only within one or more small frequency ranges which are located in the higher frequencies and/or in noisy audio signal sections, according to psycho-acoustic principles. Preferably, the allowable amplitude of the phase changes in the remaining frequency ranges is controlled according to psycho-acoustic principles. The watermark is decoded from the watermarked audio signal by correlating it with corresponding inversely transformed candidate reference phase sequences.