Audio Watermarking Techniques

Single Member - Arun Kancharla (CVN)

E6886 Spring 2005

What is watermarking?

• Audio watermarks are special signals embedded into digital audio

• They can be extracted by detection mechanisms and decoded

• They are used to track, authenticate and prevent illegal distribution and manipulation of copyright digital audio

• Audio watermarking schemes rely on imperfections of the human auditory system

• However, human ear is a very sensitive and good audio watermarking schemes are difficult to design

Desired Features of Algorithms

• Signal Processing properties– It should be unperceivable by an observer which means that the

carrier should not be altered in a perceptible way– It should be robust against intentional or anticipated

manipulations e.g. compression, filtering, resampling etc.

• Security Properties– The watermarking procedure should rely on a key to ensure

security, not on algorithms secrecy– The algorithm should be published and therefore be available for

public review– It should have a mathematical formulation to permit validation– Robustness against collusion attacks

Desired Features of Algorithms

• General Properties– The algorithm should allow real-time processing– The algorithm must be adjustable to different degrees of

robustness, quality and different amount of data– It should be tunable to different media types– It should support multiple watermarks

Goals of the Project

• Implement 3 popular audio watermarking schemes in MATLAB– Spread-Spectrum Method in Cepstrum domain: a correlation method

which embeds pseudo-random sequence into the cepstral components and detects watermark by calculating correlation between pseudo-random noise sequence and the watermarked audio signal

– Watermarking in the Time Domain: an audio masking method (in Time & Frequency) that slightly modifies the amplitude of each audio sample.

– Time-Spread Echo method: spreads an imperceptible echo using PN sequences in the time domain. Decoding uses the same secret PN sequence key.

• Evaluate merits and demerits of each scheme• Measure the trade-off between robustness to attack (additive noise,

MP3 compression), watermark strength and perceptible quality using informal tests on volunteers’ ability to detect the existence of a watermark

References

• S-K Lee and Y-S Ho, “Digital Audio Watermarking in the Cepstrum domain”, IEEE Transactions on Consumer Electronics, Vol. 46, No. 3, August 2000

• P. Bassia, I. Pitas, N Nikolaidis, “Robust Audio Watermarking in the time Domain”, IEEE Transactions on Multimedia, Vol. 3, No. 2, June 2001

• B-S Ko, R. Nishimura, Y. Suzuki, “Time-Spread Echo Method for Digital Audio Watermarking”, IEEE Transactions on Multimedia, Vol. 7, No. 2, April 2005