A DWT-Based Rational Dither Modulation Scheme for Effective Blind Audio Watermarking

A scheme jointly exploring the rational dither modulation (RDM) and auditory masking properties in the discrete wavelet transform (DWT) domain is proposed to achieve effective blind audio watermarking. The embedding of binary information is carried out by modulating coefficient vectors in the 5th-level approximation subband using the quantization steps estimated from past watermarked vectors. The robustness and payload capacity of the proposed scheme are maneuverable by varying vector dimensions, while the imperceptibility is ensured by constraining quantization noise below the auditory masking threshold. Furthermore, the periodic characteristic inherited in the RDM formulation can be used to re-establish synchronization for accurate watermark extraction. Experimental results show that the proposed DWT–RDM approach renders a near-zero objective difference grade in the perceptual evaluation of audio quality even when the signal-to-noise ratio maintains at a level near 20 dB. In most digital signal processing attacks, the bit error rates of retrieved watermarks are sufficiently low as compared to other recently developed methods with fewer payload capacities.