27-03-2014, 10:53 AM
Audio Watermarking Via EMD
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Abstract
In this paper a new adaptive audio watermarking algorithm
based on Empirical Mode Decomposition (EMD) is introduced. The audio
signal is divided into frames and each one is decomposed adaptively, by
EMD, into intrinsic oscillatory components called Intrinsic Mode Func-
tions (IMFs). The watermark and the synchronization codes are embedded
into the extrema of the last IMF, a low frequency mode stable under dif-
ferent attacks and preserving audio perceptual quality of the host signal.
The data embedding rate of the proposed algorithm is 46.9–50.3 b/s. Re-
lying on exhaustive simulations, we show the robustness of the hidden wa-
termark for additive noise, MP3 compression, re-quantization, filtering,
cropping and resampling. The comparison analysis shows that our method
has better performance than watermarking schemes reported recently.
INTRODUCTION
Digital audio watermarking has received a great deal of attention in
the literature to provide efficient solutions for copyright protection of
digital media by embedding a watermark in the original audio signal
[1]–[5]. Main requirements of digital audio watermarking are imper-
ceptibility, robustness and data capacity. More precisely, the water-
mark must be inaudible within the host audio data to maintain audio
quality and robust to signal distortions applied to the host data. Finally,
the watermark must be easy to extract to prove ownership. To achieve
these requirements, seeking new watermarking schemes is a very chal-
lenging problem [5]. Different watermarking techniques of varying
complexities have been proposed [2]–[5]. In [5] a robust watermarking
scheme to different attacks is proposed but with a limited transmission
bit rate. To improve the bit rate, watermarked schemes performed in
the wavelets domain have been proposed [3], [4]. A limit of wavelet
approach is that the basis functions are fixed, and thus they do not nec-
essarily match all real signals. To overcome this limitation, recently, a
new signal decomposition method referred to as Empirical Mode De-
composition (EMD) has been introduced for analyzing non-stationary
signals derived or not from linear systems in totally adaptive way [6].
PROPOSED WATERMARKING ALGORITHM
The idea of the proposed watermarking method is to hide into the
original audio signal a watermark together with a Synchronized Code
(SC) in the time domain. The input signal is first segmented into frames
and EMD is conducted on every frame to extract the associated IMFs
(Fig. 1). Then a binary data sequence consisted of SCs and informative
watermark bits (Fig. 2) is embedded in the extrema of a set of consec-
utive last-IMFs. A bit (0 or 1) is inserted per extrema.
Since the number of IMFs and then their number of extrema depend
on the amount of data of each frame, the number of bits to be embedded
varies from last-IMF of one frame to the following. Watermark and
SCs are not all embedded in extrema of last IMF of only one frame. In
general the number of extrema per last-IMF (one frame) is very small
compared to length of the binary sequence to be embedded.
CONCLUSION
In this paper a new adaptive watermarking scheme based on the
EMD is proposed. Watermark is embedded in very low frequency mode
(last IMF), thus achieving good performance against various attacks.
Watermark is associated with synchronization codes and thus the syn-
chronized watermark has the ability to resist shifting and cropping.
Data bits of the synchronized watermark are embedded in the extrema
of the last IMF of the audio signal based on QIM. Extensive simulations
over different audio signals indicate that the proposed watermarking
scheme has greater robustness against common attacks than nine re-
cently proposed algorithms. This scheme has higher payload and better
performance against MP3 compression compared to these earlier audio
watermarking methods. In all audio test signals, the watermark intro-
duced no audible distortion.