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Dualities in Digital Audio Compression and Digital Audio Watermarking Yi-Wen Liu , Postdoc/ Research Engineer, Boys Town National Research Hospital, Omaha, NE

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dualities in digital audio compression and digital audio watermarking

Dualities in Digital Audio Compression and Digital Audio Watermarking

Yi-Wen Liu, Postdoc/ Research Engineer,

Boys Town National Research Hospital, Omaha, NE

Keywords: masking, floating-point quantization, noise shaping, water filling, channel coding, spread spectrum, writing on dirty paper

June 28, 2007

high fidelity aac encoding at 128 kbps stereo
High fidelity AAC encoding at 128 kbps/stereo

[Remark]

2 * 44,100 samples/sec * 16 bits = 1.41 Mbps

masking presence of a tone increases threshold in its vicinity

dz

dM

Masking: Presence of a tone* increases threshold in its vicinity**
  • 1.0 Bark ~1.3mm on basilar membrane
  • Spreading function resembles the envelope travelling waves.
    • * Tonal vs. noise masker
    • ** Also check: forward- and backward-masking.
the noise shaping principle quantization error x q k x k to be masked

Psycho-acoustics

The noise shaping principle: Quantization errorX(q)[k]– X[k] to be masked

Window

X(q)[k]

X[k]

Modified Discrete Cosine Transform

Huffman coding

Bit packing

Quantization

x[n]

01001011…

Parameters

Bit allocation

jack and jill went up the hill to fetch a pail of water
Jack and Jill went up the hill to fetch a pail of water…

Rb

SMR/6dB

Nb

  • Fixed- vs. variable-rate implementation.
  • What if Rb is fractional? negative?
slide8

Image source:

Bureau of Engraving and Printing,

United States Department of the Treasury

http://www.moneyfactory.com/

applications of digital watermarks
Applications of digital watermarks
  • Copyright protection
  • Copy protection (Philips Research, 2000)
  • Transaction tracking
  • Prohibiting upload of pirated materials (YouTube/Google, 2007)
  • Broadcast monitoring
broadcast monitoring the portable people meter by arbitron inc nyse arb
Broadcast monitoring: the “portable people meter” (By Arbitron Inc., NYSE: ARB)
  • Programs (and commercials) are embedded with acoustical watermarks
  • A wearable device
    • Picks up the watermarks
    • Identifies programs
  • System tested in Houston

Image source:

http://www.arbitron.com/portable_people_meters/home.htm

arbitron s technology pseudo random watermarks spread below masking

signal spectrum

watermark

Arbitron’s technology: Pseudo-random watermarks spread below masking

signal

mark

signal +

mark

Kirovski & Malvar (2003), “Spread spectrum watermarking of audio signals,” IEEE Trans. Signal Processing.

noise is signal and signal is noise
Noise is Signal and Signal is Noise.

B

“Attack”

N

W

ENC

+

+

DEC

B*

X

Y

S

B, B*: Bit streamsW: WatermarkS: Original signal

X: Watermarked signalN: NoiseY: Corrupted copy of X

Information Capacity for discrete-timeGaussian Channel (Shannon 1948):

C = ½ log2 ( 1 + SNR ), bits per sample.

communication with random state information known at the encoder gel fand pinsker 1980

2nI(U;S)sequences

B

W: watermark

2nC files

“Attack”

N

ENC

+

+

DEC

B*

X

Y

S: music

Communication with random “state information” known at the encoder (Gel’fand & Pinsker, 1980)
  • Theorem: (Costa, 1983. “Writing on dirty paper”, Cohen & Lapidoth 2002)

If N is Gaussian i.i.d. and S is ergodic, then capacity is as high as if S were also known to the decoder.

C = maxp(u,w|s) {I(U;Y) - I(U;S)}

= ½ log2 ( 1 + <W2>/<N2>)

q uantization i ndex m odulation chen wornell 1999 2001 chou et al 2001

= 0

= 1

Image acquired from

http://cst-www.nrl.navy.mil/lattice/struk/pnma.html

Moulin et al. (2005). “Data hiding codes”.

Quantization Index Modulation(Chen & Wornell, 1999, 2001; Chou et al., 2001)

sin

s0

s1

Δs: step-size. Should be large but not too large.

we just scratched the surface
We just scratched the surface…
  • What if attack is smarter than additive noise?
    • Linear scaling & filtering
    • Audio compression
    • Time warping, pitch shifting.
    • Collusion attack, sensitivity attack, …
  • In general, it’s a game between encoder and attacker(s).
    • Encoder’s advantage: going first; to use psychoacoustics to the fullest extent.
    • Encoder’s disadvantage: going first. Attacker(s) can attempt to tamper or even erase watermark.
acknowledgement
MBI

Boys Town National Research Hospital

Douglas Keefe, Steve Neely

Stanford University

Music: Julius Smith, Marina Bosi

EE: Tom Cover

Acknowledgement