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By: Ricardo A. Garcia

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. Objectives:. Design an algorithm and implement a system capable of embedding digital watermarks into audio signals

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By: Ricardo A. Garcia

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  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. FDMA TDMA CDMA spread spectrum

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

  8. Uncoded DS/BPSK

  9. De-Spreading and Data Recovery

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

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

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

  13. Psychoacoustic Auditory Model

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

  15. Noise Shaping

  16. PROPOSED SYSTEM Transmission: watermark generation and embedding

  17. Reception: watermark recovery

  18. 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

  19. MPEG LAYER 3 Level: -2 dB

  20. 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

  21. 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

  22. 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

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