Audio Watermarking


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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.

AUDIO WATERMARKING CHARACTERISTICS

Transparency: watermark is not detectable
Robustness: survives digital processing (e.g., compression) and malicious analytical attacks.
Efficiency: low cost implementation using minimal resources
Independence: of both the type and format of multimedia data (e.g., music, speech, video, sample rates, coding scheme, ...)

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.
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