07-04-2012, 12:02 PM
Audio Watermarking
Audio_Watermarking.ppt (Size: 245.5 KB / Downloads: 50)
INTRODUCTION
Digital Data can be shared by multiple users, distributed over network, and managed for long period time without any damage.
In contrast to these, the copyright protection problem arises, since unauthorized copying and distribution of digital data are simplified, too.
As a result, a technique called digital watermarking is introduced to protect the ownership of these contents.
AUDIO WATERMARKING
Digital Audio Watermarking is a technology to hide information in an audio file without the information being audible to the listener, and without affecting in any way the audio quality of the original file.
CLASSIFICATION OF AUDIO WATERMARKING
Temporal watermarking
Temporal watermarking hides watermarks directly into digital audio signals in the time domain.
Spectral water-marking
The spectral audio watermarking applies certain frequency transform, such as FFT, DCT, and DWT, etc, to the data block of the audio signal, and hides the watermark information Into the transformed data block.
DC LEVEL SHIFTING
Here watermark is embedded by shifting the DC level of the audio signal.
An input signal is divided into frames of fixed length.
DC level of each frame =Mean of a frame-value in the frame
After that a binary watermark sequence generated randomly is introduced to the shifted signal. This is achieved by introducing a DC offset level to each frame in the signal according to the watermark bits.
If the watermark bit is 0, the signal is shifted downward.
If the watermark bit is 1, the signal is shifted upward.
DC LEVEL SHIFTING
level0=-DCBiasMultiplier x FramePower
level1=+DCBiasMultiplier x FramePower
where
level0 ->DC level introduced when a watermark bit is 0
level1 -> the DC level introduced when a watermark bit is 1.
To extract a watermark, a watermarked signal is first divided into frames. Then, the mean of each frame is calculated. If the mean of a frame is positive, the corresponding watermark bit is 1. Else, the watermark bit is 0.
The original signal and watermark is not needed in the extraction process. Therefore, DC level shifting is a blind watermarking scheme
ANALYSIS OF VARIOUS TECHNIQUES
DC level shifting algorithm
The robustness level for the DC level shifting is poor, the watermark can be easily removed by altering the DC levels of the signal and the watermark is destroyed.
Frequency Masking
This method is not robust to filtering because watermark is embedded to all frequency bands.
Attack by high pass filter MPEG can erase the watermark.
Spread Spectrum & Band Division Based On QMF
Both the band division method and the spread spectrum method are capable of defending against the MP3 compression, but the spread spectrum has a better detection rate than the band division method.