Synthesized multimedia objects are emerging everywhere now. One
can talk on the phone to a virtual representative that speaks a
synthesized tongue, drink soda of synthesized taste, such as Coke, or
even fall in love with a synthesized graphic character. It becomes
urgent to protect such objects as intelectual properties, for the
synthesis of them often involves a lot of computation power and human
labor. In my dissertation research, a framework is proposed for the
design of robust watermarking algorithms on the synthesis parameter
domain.
- [ .pdf | .ps ] "Watermarking Parametric
Representations for Synthetic Audio," in Proceedings of IEEE ICASSP 2003, Hong
Kong, China
Particularly for audio
signals that are sinusoidal in nature, such as vowels of human speech
or
sustaining tones of a musical instrument, I have been experimenting the
idea of watermarking by quantizing the frequency. To implement it, a
signal has to first be decomposed into sinusoidal and non-sinusoidal
components. Then, frequencies of sinusoidal partials are
quantized
to carry binary information. The quantization is set to be as small as
can not be heard by human ears, but meanwhile as large as possible so
that the quantization step can easily be resolved when the watermark's
binary information needs to be extracted. The frequency-quantized
sinusoids are carefully synthesized and superposed with the
non-sinusoidal components, which are un-altered, to form a watermarked
version of the original signal.
- [ .pdf | .ps
] "Audio Watermarking Based on Sinusoidal Analysis and Synthesis", in
proceedings of ISMA 2004, Nara,
Japan
To decode the watermark embedded as described above, a frequency
estimator with very high accuracy is necessary. I developed an
efficient algorithm that can track 50-100 partials from a mildly noisy
observation. The algorithm often (but not always) approaches the
Cramer-Rao lower bound, a theoretical limit in parameter estimation.
Empirically, the algorithm works well when all partials in the
spectrum are well separated to begin with.
- [ .pdf | .ps
] "Watermarking Sinusoidal Audio Representations by Quantization Index
Modulation in Multiple Frequencies", in Proceedings of IEEE ICASSP 2004, Montreal, Canada
A somewhat disjoint branch of my dissertation research in on the
theory side. I am interested in the modeling of watermarking as
what is called "writing on dirty paper" (WDP). In particular, I
am
interested in studying Shannon's data hiding limits on transimitting
multiple watermarks to a common host at multiple rates. I call it
"broadcast on dirty paper" (BDP), and demonstrated that the data hiding
capacity region is larger if one considers power-sharing rather than
time-sharing for embedding multiple watermarks. Preliminary
simulations on joint "spread-spectrum" and "quantization" watermarking
also support the power-sharing scheme.
- [ .pdf | .ps
] "Multiple watermarking: is power-sharing better than time-sharing?",
in Proceedings of IEEE ICME 2004, Taipei, Taiwan.