1. DIGITAL WATERMARKING OF AUDIO SIGNALS USING A PSYCHOACOUSTIC AUDITORY MODEL AND SPREAD SPECTRUM THEORY By: Ricardo A. Garcia University of Miami School of Music 1999

2. 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

3. Characteristics: Not perceptible (transparent) Resistant to degradation –Removal attempts –Transmission by analog/digital channel –Sub-band coders Original audio is not required in recovery

4. Design Approach:

5. SPREAD SPECTRUM Communication system –Uses all the available spectrum –Each channel uses an orthogonal code –All other channels appear as “noise”

6. TDMAFDMA CDMA spread spectrum

8. Direct Sequence Spreading Uncoded Direct Sequence Binary Phase Shift Keying Uncoded DS/BPSK

10. De-Spreading and Data Recovery

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

13. PSYCHOACOUSTIC AUDITORY MODEL Simultaneous frequency masking Calculate an approximated masking threshold T(z) LINEAR LOGARITHMIC

14. Frequency  Bark Scale Mapping Critical bands Basilar membrane spreading function B(z)

15. Psychoacoustic Auditory Model

16. Noise Shaping Replace components below masking threshold with components from watermark Level of the watermark below threshold Each band has its own scaling factor

17. Noise Shaping

18. PROPOSED SYSTEM Transmission: watermark generation and embedding

19. Reception: watermark recovery

20. 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

21. MPEG LAYER 3 Level: -2 dB

22. Listening Test Transparency was achieved for all the watermarking levels. Total listening trials: 40 level = -2 dB 24 correct identifications level = -4 dB 19 correct identifications level = -6 dB 19 correct identifications

23. 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

24. 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