Watermarking sinusoidal audio representations by quantization index modulation in multiple frequencies

The focus of the paper is to hide information in sinusoidal audio representations. Watermarks are embedded by introducing quantization index modulation (QIM) in frequencies of sinusoids. The frequency shifts due to QIM are controlled to be less than one-thirtieth Bark, which requires high accuracy in frequency estimation for watermark decoding. Therefore, the paper presents a hybrid multiple frequency estimator which consists of spectral interpolation followed by iterative square error minimization. The frequency estimator is tested in watermarking both computer generated sounds and actual recordings. The watermarks are intended to survive MP3 compression. Selected experiments are documented and discussed.