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DIGITAL WATERMARKING OF AUDIO SIGNALS USING A PSYCHOACOUSTIC AUDITORY MODEL AND SPREAD SPECTRUM THEORY *. By: Ricardo A. Garcia. MIT Media Lab Machine Listening Group. *Research done at: University of Miami School of Music 1999. Objectives:.
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DIGITAL WATERMARKING OF AUDIO SIGNALS USING A PSYCHOACOUSTIC AUDITORY MODEL AND SPREAD SPECTRUM THEORY* By: Ricardo A. Garcia MIT Media Lab Machine Listening Group *Research done at: University of Miami School of Music 1999
Objectives: • Design an algorithm and implement a system capable of embedding digital watermarks into audio signals • Use spread spectrum techniques to generate the watermark. • Use a psychoacoustic auditory model to shape the watermark
Watermark characteristics: • Not perceptible (transparent) • Resistant to degradation • Removal attempts • Transmission by analog/digital channel • Sub-band coders • Original audio is not required in recovery
Conference Overview: 1. a) Psychoacoustic Auditory Model b) Noise shaping (watermark embedding) c) Spread Spectrum watermark generation 2. Developed system 3. Examples and System Performance 4. Conclusions
a) PSYCHOACOUSTIC AUDITORY MODEL • Simultaneous frequency masking • Calculate an approximated masking threshold T(z)- frequency holes -
b) NOISE SHAPING • Replace components below masking threshold with components from a broadband noise-like signal (watermark) • Level of the watermark below threshold • Each critical band has its own scaling factor
c) SPREAD SPECTRUM • Communication system • Uses all the available spectrum (broadband, noise-like) • Each channel use an orthogonal code • All other channels appear as “noise”
FDMA TDMA CDMA spread spectrum
Information = data sequence (watermark) • Jammer = music signal (after auditory model)
Direct Sequence Spreading Uncoded Direct Sequence Binary Phase Shift Keying Uncoded DS/BPSK • Data sequence (watermark) • Modulator (fo) • PN sequence
Coded DS/BPSK • Transmitter: • Repeat Code (m) • Interleaving • Receiver: • De-interleaving • Decoder (decision rule)
2. PROPOSED SYSTEM Transmission: watermark generation and embedding
3. EXAMPLES Original Audio One watermark After Auditory Model Shaped watermark Residual Watermarked Audio
SYSTEM PERFORMANCE • Survival over different channels • MPEG, Mini Disc, Two consecutive D/A - A/D, Analog Tape, FM Stereo Radio, FM Mono Radio, FM Mono Radio (weak signal), AM Radio • (next slide) • Listening test • ABX test, 40 trials • (-2 db, 24 correct id.), (-4 db, 19), (-6 db, 19)
MPEG LAYER 3 Level: -2 dB
4. CONCLUSIONS • The perceptual quality of the audio signal was retained • The watermark signal survives to different removal attacks (redundancy) • Few parameters are needed at the receiver to recover the watermark
FURTHER RESEARCH • Performance with different types of music • Changes in the playback speed of the signal • Bit error detection and recovery • Optimal spread spectrum parameters • Multiple watermark embedding • Crosstalk interference
Contact Information • Ricardo A. Garcia • Email: rago@media.mit.edu • Website: http://www.media.mit.edu/~rago