Abstract
A watermarking system based on amplitude modulation is proposed. Sinusoidal amplitude modulations at relatively low modulation frequencies applied to neighboring subband signals in opposite phases are used as the carrier of embedded information. The embedded information is encoded in the form of relative phase differences between the amplitude modulations applied to several groups of subband signals. Robustness against perceptual codecs, additive white noise, reverberation, pitch modifications and time scale modifications was verified by computer simulation using 100 pieces in a music genre database. Listening tests to measure the detection thresholds of watermarking and a subjective assessment of the slight reduction of audio quality due to watermarking were conducted using trained listeners. The results of both the listening tests and the computer simulation showed that the quality degradation caused by watermarking with moderate embedding intensity was perceptible but not annoying, while maintaining sufficient detectability of the watermarks.
