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
Dec 26, 2015
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 LabMachine 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 Modelb) 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 -
0 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4c ritic a l ban d ra te [B ark s]z
6 0
4 0
2 0
0Exc
itatio
n le
vel [
dB]
Psychoacoustic Auditory Model
F F T P o w er S p ec tru m
E n erg y p er C r itica l B a n d
S p re a d M a sk in gA c r o ss
C r it ic a l B a n d s
M a s k in gT h re sh o ldE s tim a te
N o ise S h a p in g
IF F T
s(t) S (j ) S p (j )
S p z(z )
B (z)
S m (z)
T (z)
N (j )
O U T (j )ou t(t)
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”
F R E Q U E N C YT IM
E
CO
DE
F R E Q U E N C Y T IME
CO
DE
F R E Q U E N C YT IM
E
CO
DE
TDMAFDMA
CDMAspread spectrum
T ra n sm itte r R e c e iv e r
Ja m m e r
• Information = data sequence (watermark) • Jammer = music signal (after auditory model)
Direct Sequence SpreadingUncoded Direct Sequence Binary Phase Shift Keying
Uncoded DS/BPSK
P NG ene rator
B P S KM o d u la to r
d (t) x (t)
c (t)
s (t)
• Data sequence (watermark)
• Modulator (fo)
• PN sequence
De-Spreading and Data Recovery
P NG en erato r
x(t)
c(t)
J(t)
y(t) r(t) ri d t
bT
0
Tran sm issio nC h ann el
)cos(2
0tTb
Coded DS/BPSK
• Transmitter:– Repeat Code (m) – Interleaving
• Receiver:– De-interleaving– Decoder (decision rule)
,,,,,,,
,,,,,,,
,,,,
2111332
1321321
dabcadb
cbbbaaa
dcba
2. PROPOSED SYSTEMTransmission: watermark generation and embedding
W AT E R M A R KG E N E R AT IO N
C o d ed D S /B P S K
P S Y C H O A C O U S T ICA U D IT O R Y
M O D E L
W AT E R M A R KS H A P IN G
A N D E M B E D D IN G
1 0 11 0 ...1 0 0 1
W A T E R M A R K(b it s tre a m )
A U D IO
W A T E R M A R K E DA U D IO
T (z ) T R A N S M I S S I O NC H A N N E L
PA R A M E T E R S
Reception: watermark recovery
T (z ) r (t )A U D IT O R Y
M O D E L
D E -S P R E A D I N GA N D
R E C O V E R Y
A D A P T IV EH IG H
R E S O L U T IO ND E T E C T IO N
R E S ID U A LG E N E R AT IO N
H E A D E RG E N E R AT IO N
1 0 11 0 ...1 0 0 1
T R A N S M IS S IO NC H A N N E L
R E C O V E R E DW A T E R M A R K
PA R A M E T E R S
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)
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: [email protected]
– Website: http://www.media.mit.edu/~rago