Robust multiple stereo audio watermarking for copyright protection and integrity checking

This paper presents a robust, stereo audio signal watermarking algorithm. The inter-channel redundancy of stereo audio signal is exploited by calculating average and difference signals from the LR channels of stereo audio. Discrete Wavelet Transform (DWT) followed by Discrete Cosine Transform (DCT) are applied to both average and difference signals. Few selected transform domain coefficients of average signal are used for embedding a robust watermark along with synchronization codes. A semi-fragile watermark is embedded for integrity check in a few of the transform domain coefficients of difference signal. Quantization technique is used for embedding. As both average and difference signals are used for embedding, the watermark will spread evenly in both LR channels without interfering each other. As more signal energy is concentrated in average signal compared to difference signal, larger quantization step size can be used for embedding watermark in average signal. As both the channels are used for embedding, high data payload is achieved. The proposed scheme is blind where both the watermarks are extracted independently without using the original audio. Extensive experimental results assure that the proposed watermarking scheme provides high SNR and is highly robust to common attacks like, MP3 compression, cropping, time shifting, filtering, resampling and re-quantization.