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Title

Study on suitable‑architecture of IIR all‑passfilter for digital‑audio watermarking techniquebased on cochlear‑delay characteristics

Author(s)KOSUGI, Toshizo; HANIU, Atsushi; MIYAUCHI, Ryota;
UNOKI, Masashi; AKAGI, Masato

Citation

2011 International Workshop on Nonlinear
Circuits, Communication and Signal Processing(NCSP'11): 135‑138

Issue Date

2011‑03‑01

Type

Conference Paper

Text version

publisher

URL

http://hdl.handle.net/10119/9977

RightsThis material is posted here with permission of
the Research Institute of Signal Processing
Japan. Toshizo KOSUGI, Atsushi HANIU, Ryota
MIYAUCHI, Masashi UNOKI, and Masato AKAGI, 2011
International Workshop on Nonlinear Circuits,
Communication and Signal Processing (NCSP'11),
2011, pp.135‑138.

Description

Japan Advanced Institute of Science and Technology

2011 International Workshop on Nonlinear Circuits,
Communication and Signal Processing
NCSP'11, Tianjin, China, March 1-3, 2011

Study on suitable-architecture of IIR all-pass filter for digital-audio watermarking techniquebased on cochlear-delay characteristics
Toshizo KOSUGI, Atsushi HANIU, Ryota MIYAUCHI, Masashi UNOKI, and Masato AKAGISchool of Information Science, Japan Advanced Institute of Science and Technology
1-1 Asahidai, Nomi, Ishikawa, 923-1292 Japan
TEL/FAX:+81-761-51-1391/+81-761-51-1149
Email:{s0910023, a-haniu, ryota, unoki, akagi}@jaist.ac.jp

Abstract

This paper proposes a composite architecture by reasonably incorporating parallel and cascade architectures to further improve embedding limitations with our proposed approach. We used objective evaluations to systematically investigate and confirm the advantages of the proposed approach.

We investigated embedding limitations with our proposed
method of audio watermarking. This method was based on
the concept of embedding inaudible watermarks into an original sound by controlling its phase characteristics in relation tocochlear delay. We improved the original method by designing a composite architecture for cochlear-delay filters. We
2. Composite architectureevaluated the methods to investigate the embedding limitations by carrying out four objective experiments, i.e., with
A cochlear-delay filter is designed as the following 1stPEAQ, LSD, bit-detection, and robustness tests. The results order IIR all-pass filter to model cochlear delay characterisindicated the embedding limitation with the composite archi- tics [6]:tecture in the best case was 256 bps, while the embedding
limitations with the parallel and cascade architectures were−b + z −1H(z)=,0 < b < 1.
(1)
192 and 128 bps, respectively.
1 − bz −1
1. Introduction
Digital-audio watermarking has recently been focused on
as a state-of-the-art technique enabling copyright to be protected. This has aimed to embed codes to protect the inseparable and inaudible copyright codes separable by users, andto detect embedded codes from watermarked signals [1, 2].
Watermarking methods must satisfy three requirements toprovide a useful and reliable form of copyright protection:(a) inaudibility, (b) confidentiality, and (c) robustness. Although several methods (such as LSB [2], DSS [3], ECHO[4], and PPM [5]) have been proposed, these methods havesuffered from serious drawbacks in either of the three requirements, especially in (a) inaudibility and (c) robustness due toembedding or reduced security [2].
As the first step toward solving the problems with regard
to requirements (a) and (c), a method of audio watermarking based on cochlear delay has been proposed by Unoki &Hamada [6] (a base architecture). Imabeppu et al. investigated embedding limitations with their proposed approaches
by carrying out four objective experiments [7]. We then improved the proposed method by designing parallel and cascade architectures for cochlear-delay filters [8]. As a result,our proposed architectures made it possible to increase embedding limitations from those with the base architecture.

An IIR all-pass filter is usually used to control delays in which
amplitude spectra are passed equally without any loss. Here,the group delay, τ (ω), can be obtained as:τ (ω) = −darg(H(ejω ))
,
dω

(2)

where H(ejω ) = H(z)|z=ejω . The τ (ω) is fitted to thecochlear delay (scaled by 1/10 as indicated by the dashed line
Fig. 2). Here, this architecture is referred to as a base architecture.
Imabeppu et al. improved the previous approach to improve embedding limitations with the method by using a parallel architecture [7]. Based on the expression of N -bits, it
is also possible to control M (= 2N )-th cochlear delays using the parallel architecture. However, M -th cochlear delays
must not be beyond the cochlear delay, which was scaled by
1/10. We have improved our previous approach to improveembedding limitations with the method by using a cascadearchitecture [8]. Based on the expression of L-bits, it is also
possible to control R(= 2L )-th cochlear delays using the cascade architecture. However, inaudibility is affected increasing the number of R-th cochlear delays. In addition, the valueof parameter b must be from 0 to 1. Thus, we propose a composite architecture by reasonably incorporating parallel andcascade architectures. Based on the expression of N · L-bits,- 135 -

(a) Data embedding
Original
signal, x(n)H1,m (z)1.6

HCmp (z)Hl,m (z)...

...

HL,m (z)Watermarked
signal, y(n)τ2,3 ("11")

Embedded signal,s(k)=01010001010110...
Weighting function
L N-bits/frame
Frame number(b) Data detection
Watermarked
Y(ω)
Φ(ω)
signal, y(n)p =arg min{ΔΦp } Detected codearg
FFT={s(k)}, L N-bits+ΔΦ p =|Φ-arg H p | |Original
signal, x(n)

arg

FFT

-

τCmp=τ1,2+τ2,3 ("1011")

Group delay (ms)

1.2
1
0.8
0.6
0.4

{s(k)}=
dec2bin( p, L N )X(ω)

Cochlear delay (1/10)
τ1,2 ("10")

1.4

0.2
0
−2
10

Figure 1: Block diagram of composite architecture.

−1

10

0

10

1

10

Frequency (kHz)it is also possible to control U (= 2N ·L )-th cochlear delays
using the composite architecture.

Figure 2: Cochlear-delay and group-delay characteristics ofcomposite architecture (L = 2 and N = 2).

2.1. Data embedding process

data. (5) The embedded data, ŝ(k), are detected using the
Figure 1(a) has a block diagram of the data-embedding pro- p-th cochlear filter.
cess. We designed the composite architecture for the cochlearϕ(ωq ) = arg Y (ωq ) − arg X(ωq )(6)delay filter HCmp (z) as follows:
∑
jωq
∆Φp =
|ϕ(ωq ) − arg(Hp (e ))|
(7)
L
L
∏
∏
−bℓ,m + z −1qHCmp (z) :=Hℓ,m (z) =(3)
1 − bℓ,m z −1
ℓ=1

ℓ=1

where ℓ = 1, 2, · · · , L and m = 0, 1, · · · , M − 1. Here, thegroup delay, τCmp (ω), can be obtained as:τCmp (ω)=

L∑

τℓ,m (ω)(4)ℓ=1

τℓ,m (ω)=−

d arg(Hℓ,m (ejω ))dω(5)

3. Evaluations
We evaluated the improved methods (the parallel (N =1, 2, 3, and 4), the cascaded (L = 1, 2, 3, and 4), and thecomposite architectures (L = 2 and N = 2)) by carrying out
four objective experiments, i.e., with perceptual evaluation ofsound quality (PEAQ) [10], Log spectrum distortion (LSD),
bit-detection, and robustness tests to investigate the extent ofembedding limitations with the improved methods.

For example, the group delays in the composite architecturewith N = 2 and L = 2 are represented as 16-types of 3.1. Objective evaluations
τCmp (ω) in Eq. 5. Therefore, the composite architecture can
All 102 tracks in the RWC music-genre database [9]embed 4-bits per frame into the original signal. Figure 2 plots
the group-delay characteristics of the cochlear delay filter in were used in these evaluations. The original tracks had
a 44.1-kHz sampling frequency, 16-bit quantization, andthe composite architecture.
two-channels (stereo). Here, the unit of fps represents
frames per sec. The same watermarks with eight letters2.2. Data detection process(“AIS-Lab.”) were embedded into both channels by usFigure 1(b) shows the flow for the data-detection process ing the proposed methods. The frame-rates in these experwe used. Watermarks were detected as follows: (1) We as- iments were 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096,
sume that both x(n) and y(n) are available with this wa- and 8192 fps.
termarking method. (2) The original, x(n), and the waterWe carried out the first objective experiment (PEAQ)
marked signal, y(n), are decomposed to become overlapping to evaluate the sound quality of the watermarked signals.
segments using the same window function used in embedding PEAQs were used to output the objective difference grades
the data. (3) The phase difference, ϕ(ω), is calculated in each (ODGs). The ODGs were graded on a five-point scale assegment, using Eq. (6). (4) The summed phase differences of 0 (imperceptible), −1 (perceptible but not annoying), −2
ϕ(ω) to the respective phase spectrum of the filters, (∆Φp ), (slightly annoying), −3 (annoying), and −4 (very annoying).
are calculated as in Eq. (7) to estimate the group delay char- An evaluation threshold of −1 was chosen to evaluate inaudiacteristics of (HCmp (z) = Hp (z)) used for embedding the bility in this experiment. Figures 3(a), 4(a), and 5(a) plot the- 136 -

1

0

0

PEAQ

PEAQ

1

−1
−2
−3
−4

(a)
4

−1
−2
−3

8

16

32

64

−4

128 256 512 1024 2048 4096 8192

1.5

Bit−detection rate (%)

8

16

32

64

128 256 512 1024 2048 4096 8192

8

16

32

64

128 256 512 1024 2048 4096 8192

LSD (dB)

(b)

0.5

4

8

16

32

64

100

(c)

80
L=1, N=1
L=1, N=2
L=1, N=3
L=1, N=4

60

4

8

16

32

64

1

0.5

0

128 256 512 1024 2048 4096 8192

Bit−detection rate (%)

LSD (dB)

(b)

40

4

1.5

1

0

(a)

128 256 512 1024 2048 4096 8192

Frame rate (fps)

4

100

(c)

80
L=1, N=1
L=2, N=1
L=3, N=1
L=4, N=1

60
40

4

8

16

32

64

128 256 512 1024 2048 4096 8192

Frame rate (fps)Figure 3: Evaluations of parallel architectures (N = 1, 2, 3, Figure 4: Evaluations of cascade architectures (L = 1, 2, 3,
and 4): (a) PEAQ, (b) LSD, and (c) bit-detection rate.
and 4): (a) PEAQ, (b) LSD, and (c) bit-detection rate.

averaged ODGs of the PEAQs. Figures 3(a) and 4(a) showthat the ODGs of the PEAQs have decreased with an increasein the number of cochlear-delay filters.The PEAQs in a composite architecture (L = 2 and N = 2) were under the evaluation threshold (> −1) in which the frame rates ranged from4 to 64 fps.
We carried out the second objective experiment (LSD measures) to evaluate the sound quality of the watermarked signals. Figures 3(b), 4(b), and 5(b) plot the averaged LSD for
the watermarked signals. The LSDs in the cascade architectures (L = 1, 2, 3, and 4) were under the evaluation threshold(< 1 dB) in which the frame rates ranged from 4 to 2048 fps,
while the LSDs in the parallel architectures (N = 1, 2, 3, and4) were under the threshold in which the frame rates ranged
from 4 to 4096 fps. The LSDs in a composite architecture(L = 2 and N = 2) were under the evaluation threshold (< 1dB) in which the frame rates ranged from 4 to 1024 fps.
We carried out a bit-detection test in the third objective
experiment to evaluate how much embedded data could be
detected from the watermarked audio signals. An evaluation threshold of 75% was chosen as the embedding limitation to evaluate the bit-detection rate in this experiment. Figures 3(c), 4(c), and 5(c) plot the averaged bit-detection rate
for the watermarked signals. The detection rates in the parallel architectures (N = 1, 2, 3, and 4) were over the evaluation threshold (> 75%) in which the frame rates ranged
from 4 to 256 fps. The detection rates in the cascade architectures (L = 1, 2, 3, and 4) were over the evaluation threshold(> 75%) in which the frame rates ranged from 4 to 128 fps.

The detection rates in the composite architecture (L = 2 andN = 2) were over the evaluation threshold (> 75%) in which
the frame rates ranged from 4 to 256 fps.
The results revealed that the most optimal parallel, cascade,and composite architectures corresponded to (N, L)=(2, 1),(1, 2), and (2, 2), where the maximum detection rate for thecomposite architecture was 64 fps when it represented 4-bits
per frame. Therefore, the embedding limitation with the composite architecture was 256 (= 64 fps ×4) bps.
3.2. Evaluation of robustness
We carried out three types of robustness tests in the
fourth experiment to evaluate how well the methods could
accurately and robustly detect embedded data from thewatermarked-audio signals. The manipulation conditions weused were: (i) down sampling (44.1 kHz → 20, 16, and 8kHz), (ii) amplitude manipulation (16 bits → 24-bit extension
and 8-bit compression), and (iii) data compression (mp3: 128kbps, 96 kbps, and 64 kbps-mono).
Table 1 lists the results of evaluations for the base, parallel, cascade, and composite architectures. It summarizes the
maximum fps over the evaluation threshold (> 75%) of bit
detection. The maximum detection rate with all architectures
decreased when the signals were compressed by mp3 with 96kbps. Here, the maximum detection rates were 32 and 64 fps
with the parallel (N = 4) and composite architecture (L = 2
and N = 2), respectively. The bit detection rate with thecascade architecture (L = 4) did not exceed the evaluation- 137 -

Table 1: Results of robustness tests on embedding limitations (frame per sec (fps)).
Base
L = 1, N = 1
512
256
256
128
256
256
128
64
128

Modification
Non-process
DS 20 kHzDS 16 kHzDS 8 kHzBC 24 bits
BC 8 bits
mp3 128 kbps
mp3 96 kbps
mp3 64 kbps

Parallel Architecture
L = 1, N = 2 L = 1, N = 3 L = 1, N = 4
512
512
256
256
256
128
256
256
128
128
128
64
256
256
128
256
256
128
128
128
64
64
64
32
128
64
64

PEAQ

0
−1
−2

−4

(a)
4

8

16

32

64

128 256 512 1024 2048 4096 8192

1

Acknowledgments This work was supported by aGrant-in-Aid for Challenging Exploratory Research (No.
21650035) made available by the JSPS.

0.5

References

1.5

LSD (dB)(b)0

Bit−detection rate (%)

Composite Arc.
L = 2, N = 2
256
128
128
64
128
64
64
64
64

chitecture (L = 2 and N = 2) was 256 (= 64 fps ×4) bps.
Both results revealed that the composite architecture (L = 2
and N = 2) was the optimal architecture for the proposed approach.Therefore, the embedding limitations were improved
to architecture of the cochlear delay filter (L and N ) by optimal choice.

1−3

Cascade Architecture
L = 2, N = 1 L = 3, N = 1 L = 4, N = 1
256
256
128
128
128
64
128
128
64
128
64
64
128
128
128
128
128
64
128
64
32
64
32
—
64
64
32

4

8

16

32

64

[1] STEP2001. “News release, Final selection of technology
toward the global spread of digital audio watermarks,”
http://www.jasrac.or.jp/ejhp/release/2001/062 9.html.

128 256 512 1024 2048 4096 8192

100

(c)

[2] N. Cvejic and T. Seppänen, Digital audio watermarking techniques and technologies, IGI Global, Hershey, PA 2007.

80

40[3] Boney, L., Tewfik, H. H., and Hamdy, K. N., “Digital watermarks for audio signals,” Proc. ICMCS, pp. 473–480, 1996.

L=1,N=4
L=4,N=1
L=2,N=2

60

4

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16

32

64

[4] Gruhl, D., Lu, A., and Bender, W., “Echo Hiding,” Proc. Information Hiding 1st Workshop, 295–315, 1996.

128 256 512 1024 2048 4096 8192

Frame rate (fps)Figure 5: Evaluations of composite architectures ((L, N ) =(1, 4), (4, 1), and (2, 2)): (a) PEAQ, (b) LSD, and (c) bitdetection rate.
threshold at any frame-rate.
4. Conclusions[5] Nishimura, R., and Suzuki, Y., “Audio watermark based on
periodical phase shift.” J. Acoust. Soc. Jpn., Vol. 60, No. 5,
pp.269–272, 2004.
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[7] Imabeppu, K., Hamada, D., and Unoki, M., “Embedding limitations with audio-watermarking method based on cochlear
delay characteristics,” Proc. IIHMSP2009, 82–85, 2009.

We investigated how the proposed approach could be im- [8] Unoki, M., Kosugi, T., Haniu, A., and Miyauchi, R., “Design
plemented to produce an efficient architecture to further imof IIR all-pass filter based on cochlear delay to reduce embedprove embedding limitations with our proposed approach.
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N = 2) and cascade architecture (L = 2 and N = 2) were
BS.1387: Perceptual evaluation of audio quality,” TSP Lab.
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revealed that embedding limitations with the composite ar-- 138 -