DIGITAL WATERMARKING OF AUDIO SIGNALS USING A PSYCHOACOUSTIC AUDITORY MODEL AND SPREAD SPECTRUM THEORY * By: Ricardo A. Garcia *Research done at: University of Miami School of Music 1999 MIT Media Lab Machine Listening Group

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 -

Psychoacoustic Auditory Model

Masking Threshold T(z)

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

Noise Shaping

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”

TDMAFDMA 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 (f o ) PN sequence

Uncoded DS/BPSK

De-Spreading and Data Recovery

Coded DS/BPSK Transmitter: –Repeat Code (m) –Interleaving Receiver: –De-interleaving –Decoder (decision rule)

2. PROPOSED SYSTEM Transmission: watermark generation and embedding

Reception: watermark recovery

3. EXAMPLES Original Audio After Auditory Model Residual One watermark Shaped watermark 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 – –Website: