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

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

9. Uncoded DS/BPSK

10. De-Spreading and Data Recovery

11. Coded DS/BPSK Transmitter: Receiver: Repeat Code 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