08-17-2017, 12:42 AM
Digital Audio Watermarking
Digital watermarking is a technology which allows a secret message to be hidden in a computer file, without the detection of the user.Digital audio watermarking involves the concealment of data within a discrete audio file. Intellectual property protection is currently the main driving force behind research in this area though there are a lot of other applications. To combat online music piracy, a digital watermark could be added to all recording prior to release, signifying not only the author of the work, but the user who has purchased a legitimate copy. The DRM software will ensure that the user has paid for the song by comparing the watermark to the existing purchased licences on the system.
DC Watermarking Scheme
The DC watermarking scheme hides watermark data in lower frequency components of the audio signal, which are below the perceptual threshold of the human auditory system.
Watermark Insertion
The process of inserting a digital watermark into an audio file can be divided into four main processes which are:
1)Framing,:Here, The audio file is portioned into frames which are 90 milliseconds in duration. This frame size is chosen so that the embedded watermark does not introduce any audible distortion into the file.
2)spectral analysis(FFT):
we perform spectral analysis on the signal, consisting of a fast Fourier transform (FFT), which allows us to calculate the low frequency components of each frame, as well as the overall frame power.
3)DC carrier removal
4)Watermark signal addition.From the spectral analysis completed previously, we calculated the spectral power for each frame, which allows us to examine the low frequency power in each frame and subsequently extract the watermark,
Limitations:
robustness and data density causes the limitations. The robustness of the scheme can be increased somewhat with longer audio files, by inserting the watermark signal multiple times, which will aid in extraction. higher hidden data density in the watermarked signal can be achieved by more advanced techniques such as spread spectrum, phase encoding, or echo hiding .
[b]Other Watermarking Techniques
Phase Encoding[/b]
This watermarking technique exploits the human auditory system s lack of sensitivity to absolute phase changes by encoding the watermark data in an artificial phase signal.The the audio signal is broken down into into frames, and performing spectral analysis on each frame.
Spread Spectrum Watermarking
This watermarking technique relies on direct sequence spread spectrum (DSS) to spread the watermarked signal over the entire audible frequency spectrum such that it approximates white noise, at a power level as to be inaudible. a carrier wave which creates the spread signal watermark code modulates the signal using the pseudorandom sequence (chip).
Echo Watermarking
It relies on distorting an audio signal in a way which is perceptually dismissed by the human auditory system as environmental distortion.The original audio signal is copied into two segments called kernels -one which leads the original signal in time, and one which lags.
For more details, visit:
http://ece.uvic.ca/ aupward/w/watermarking.htm
http://patentstorm.us/patents/7565296/fulltext.html
http://herkules.oulu.fi/isbn9514273842/i...273842.pdf