Survey of Spread Spectrum Based Audio Watermarking Schemes

Survey of Spread Spectrum Based Audio Watermarking Schemes

DOI: 10.4018/978-1-61520-925-5.ch006

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6.1 Basic Direct Sequence Spread Spectrum

Cox et al. (1997) proposed a secure robust watermarking approach for multimedia based on spread spectrum technology. Although their system was originally proposed for watermarking images the basic idea also applies to audio watermarking.

The watermarking procedure proceeds as follows:

From host signal, a sequence of values x={xi} is extracted, which is used for inserting secret message m={mi}. The watermarked sequence is denoted as 978-1-61520-925-5.ch006.m01 and inserted back into the place of x to obtain a watermarked signal y. During transmission, possible distortion or attacks may affect y and the received signal is now denoted as 978-1-61520-925-5.ch006.m02, which may not be identical to y. Assume the host signal is available at the decoder side, a probably altered watermarked sequence 978-1-61520-925-5.ch006.m03 is first extracted from the received signal 978-1-61520-925-5.ch006.m04. A possibly corrupted message m* is extracted from w* and compared to m for statistical significance. (Cox et al., 1997).

During watermark embedding, a scaling parameter α which controls the watermark strength is specified and used in the watermark embedding equation. Three embedding formulae used are

978-1-61520-925-5.ch006.m05
(6.1)
978-1-61520-925-5.ch006.m06
(6.2)
978-1-61520-925-5.ch006.m07
(6.3)

Equation (6.2) is used in (Cox, 1997) with α = 0.1.

The similarity between the extracted watermark and the embedded watermark is measured by

978-1-61520-925-5.ch006.m08
(6.4)

Large values of 978-1-61520-925-5.ch006.m09 are important and typically if 978-1-61520-925-5.ch006.m10 then a watermark is detected in the received signal.

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6.2 Time Domain Spread Spectrum Watermarking Scheme

Cvejic et al. (2004) proposed an alternative audio spread spectrum watermarking scheme in the time domain. The embedding part is illustrated in Figure 1.

Figure 1.

Spread spectrum watermarking in the time domain (Cvejic, 2004)

978-1-61520-925-5.ch006.f01

Time domain masking properties of the HAS are used to maximize the amplitude of the watermark to be embedded, which increases robustness during detection, while still keeping the watermark imperceptible and maintaining high perceptual audio quality.

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