Adaptive Wavelet Quantization Index Modulation Technique for Audio Watermarking

The quantization index modulation (QIM) that is often used in watermarking can provide a tradeoff between robustness and transparency. In this paper, we propose a robust audio watermarking technique which adopts the wavelet QIM method with adaptive step sizes for blind watermark extraction. Since wavelet transform offers both temporal and frequency resolutions, it is suitable for audio signal processing. The adaptive step size technique is applied to audio signals with different characteristics. This technique is designed based on the criterion that SNR must be maintained above 20 dB so that it is robust and transparent. No side information on the step sizes need to be transmitted. The experimental results show that the embedding capacity is around 4 bits/frame and the watermark is robust against MP3 compression at 64 Kbps, resampling, requantization, and Gaussian noise corruption. The NC values after attacks are all above 0.8 in the experiments so that the copyright can easily be distinguished.