Nhut Minh Ngo

Robust and reliable audio watermarking based on phase coding

This paper proposes a novel robust audio watermarking method based on phase coding. The quantization index modulation technique is employed for embedding watermarks into the phase spectrum of audio signals. To increase robustness of the proposed method, the region of phase spectrum that is resistant against attacks is selected for embedding. We experimentally analyzed the phase spectrum to find out which region is not distorted under attacks. On the other hand, the quantization step size is suitably selected so that the modification of phase does not cause severe distortion in sound quality. The experimental results show that the watermarks could be kept inaudible in audio signals and robust against attacks. The proposed method has the ability to embed watermarks into audio signals up to 400 bits per second with a bit error rate of less than 1%.

Watermarking for Digital Audio Based on Adaptive Phase Modulation

This paper proposes a novel blind watermarking method for digital audio based on adaptive phase modulation. Audio signals are usually non-stationary, i.e., their own characteristics are time-variant. The features for watermarking have not been selected by combining the principle of variability, which affects the performance of the whole watermarking system. The proposed method embeds a watermark into an audio signal by adaptively modulating its phase with the embedded bit ‘0’ or ‘1’ using two all-pass filters. The frequency location of the filter pole-zero which characterizes the transfer function of the filter is adapted to distribution of signal power spectrum. The filter pole-zero locations are adapted in such a way that phase modulation causes the least distortion in watermarked signals to achieve the best sound quality. The experimental results show that the proposed method could embed inaudible watermark into various kinds of audio signals and correctly detect watermark without the aid of original signals. The proposed method has the ability to embed watermark into audio signals up to 150 bits per second with the bit error rate of less than 10 %.

Robust and reliable audio watermarking based on dynamic phase coding and error control coding

This paper proposes an audio watermarking method based on dynamic phase coding and error control coding. The technique of quantization index modulation is employed for embedding watermarks into the phase spectrum of audio signals. Since most of the audio information is distributed in moderately low frequencies, to increase robustness, this frequency region is chosen for embedding watermarks. Phase modification causes sound distortion in a manner that is proportional to the magnitude. Therefore, the amount of phase modification is adjusted according to the magnitude to balance inaudibility and robustness. Error control coding is incorporated to further increase reliability of watermark detection. The experimental results show that the watermarks could be kept inaudible in watermarked signals and robust against various attacks. Error control coding is effective in increasing watermark detection accuracy remarkably.

Data-hiding Scheme for Digital-audio in Amplitude Modulation Domain

This paper proposes an audio-data hiding scheme for amplitude-modulation (AM) radio broadcasting systems. The digital-audio method of watermarking based on cochlear delay (CD) that we previously proposed is employed in this scheme to send an inaudible message. We investigate the feasibility of a data-hiding scheme in the AM domain by applying the method of CD-based inaudible watermarking. The proposed scheme embeds both original and watermarked signals as lower and upper sidebands into the AM signals by using the method of double-sideband with carrier (DSB-WC) and then transmits them to the receivers. Particular receivers in the proposed scheme can detect both original and watermarked signals by demodulating both sidebands with DSB-WC and then extract messages from the watermarked signal with the original signal using CD-based watermarking. The results we obtained from computer simulations revealed that the proposed scheme can transmit messages as watermarks in AM radio systems and then correctly extract the messages from AM signals. The results also indicated that the sound quality of the demodulated signals could be kept at higher levels not only with the proposed scheme but also in traditional AM radio systems. This means that the proposed scheme has the possibility of acting as a hidden-message transmitter as well as having low-level compatibility in AM radio systems.