Digital audio recorded give us many advantage in data processing or manipulation. However, it is also avoid violation of audio data royalty; for example illegally duplicating, cropping half or all of data and distributing without permission from owner of audio data. Watermarking technique can be implemented to protect its digital audio recorded.
Digital Watermarking Watermarking is the process that embeds data called a watermark, tag or label into a multimedia object such that watermark can be detected or extracted later to make an assertion about the object. The object may be an image or audio or video. It may also be text only
They primarily differ by intent of use. A watermark can be perceived as an attribute of the carrier (cover). It may contain information such as copright, license, trackning and authorship etc. Whereas in case of steganography, the embedded message may have nothing to do with the cover. In steganography an issue of concern is bandwidth for the hidden message whereas robustness is of more concern with watermarking.
Watermarks and watermarking techniques can be divided into various
categories in various ways. The watermarks can be applied in spatial
domain. An alternative to spatial domain watermarking is frequency
domain watermarking. It has been pointed out that the frequency domain
methods are more robust than the spatial domain techniques. Different
types of watermarks are shown in the figure below.
Types of watermarking techniques
Low-bit coding is the simplest way to embed data into other data structures. By replacing the least significant bit of each sampling point by a coded binary string,we can encode a large amount of data in an audio signal. Ideally, the channel capacity is 1 kb per second (kbps) per 1 kilohertz (kHz), e.g., in a noiseless channel, the bit rate will be 8 kbps in an 8 kHz sampled sequence and 44 kbps in a 44 kHz sampled sequence. In return for this large channel capacity, audible noise is introduced. The impact of this noise is a direct function of the content of the host signal, e.g., crowd noise during a live sports event would mask low-bit encoding noise that would be audible in a string quartet performance. Adaptive data attenuation has been used to compensate this variation.
The major disadvantage of this method is its poor immunity to manipulation. Encoded information can be destroyed by channel noise, resampling, etc.,unless it is encoded using redundancy techniques.In order to be robust, these techniques reduce the data rate, often by one to two orders of magnitude. In practice, this method is useful only in closed, digital to digital environments.
Echo hiding schemes embed watermarks into a host signal by adding
echoes to produce watermarked signal. The nature of the echo is to add
resonance to the host audio. Therefore the acute problem of sensitivity
of the HAS towards the additive noise is circumvented in this method.
After the echo has
been added, watermarked signal retains the same statistical and
perceptual characteristics. The offset (or delay) between the original
and a watermarked signal is small enough that the echo is perceived by
the HAS as an added resonance. The four major parameters, the initial
amplitude, decay rate, "one" offset and "zero" offset are given in
Parameters of echo embedding watermarking method
The watermark embedding process can be represented as a system that
has one of two possible system functions. In the time domain, the system
functions are discrete time exponentials, differing only in the delay
between impulses. Processing host signal through any kernel will result
in an encoded signal. The delay (number of sample intervals) between the
original signal and the echo is dependent on the kernel being used, 1
if the "one" kernel is used and 0 if the "zero" kernel is used.
The host signal is divided into smaller portions for encoding more than
one bit. Each individual portion can then be considered as an
independent signal and echoed with the desired bit. The final
watermarked signal (containing several bits) is a composite of all
independently encoded signal portions. A smooth transition between
portions encoded with different bits should be adjusted using different
methods to prevent abrupt changes in the resonance in the watermarked
signal. Information is embedded into a signal by echoing the original
signal with one of two delay kernels. Therefore, the extraction of the
embedded information is to detect the spacing between the echoes. The
magnitude of the autocorrelation of the encoded signal’s cepstrum
where F represents the Fourier Transform and F¡1 the inverse Fourier Transform can be examined at two locations, corresponding to the delays of the "one" and "zero" kernel, respectively. If the autocepstrum is greater at ±1 than it is at ±0, an embedded bit is decoded as "one". For the multiple echo hiding, all peaks present in the autocepstrum are detected. The number of the peaks corresponding to the delay locations of the "one" and "zero" kernels are then counted and compared. If there are more peaks at the delay locations for the "one" echo kernel, the watermark bit is decoded as "one".
Watermarking Application Extract Mark form
Low Bit Coding Technique result very little degradation of perceptual quality so the audience cant feel the different, in contrary Echo Hiding method occur much degradation of perceptual quality than Low Bit Coding Technique. Audience can hear the different between watermarked audio and original audio
In embedding test, Low Bit Coding Technique can embed data in very large of space, but Echo Hiding only can embedd small part of data.
In extraction test , Low Bit Coding Technique always have recovery rate with 100% accuracy, but in Echo Hiding technique, watermark recovery rate depend on initial amplitude and cover audio used. There is no change in size of audio file before and after watermarking process.
In robustness test result that Echo hiding Technique have highly robustness than Low Bit Coding Technique.
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