Information Technology Reference
In-Depth Information
Fig. 5.
Constellation of OFDM symbols. Scattered circles are the noise-contaminated signal
Fig. 6.
Relationship between SNR and BER
Linear Filtering.
The watermarked signal was passed through a low-pass filter prior
to detection. A 9th-order Butterworth filter was used. For any type of signal and
modulation scheme, error-free recovery of the embedded data was achieved provided
the cut-off frequency was above the high end of the watermark band.
MP3 Coding.
Robustness against MP3 coding is important for audio watermarking.
Five pieces of hi-fi music (I~III: classic music, IV and V: pop songs) were tested in
the experiment. Parameters were the same as that in Table 2, with
1. In Table 3,
the bit error rates obtained at different compression rates and for different music are
given. Two BER values are shown in each case, where the left and right values corre-
spond to the watermark bands [W/4, W/2] and [W/4, 3W/8], respectively.
It is concluded from this experiment that, when using QAM, the system is robust
against MP3 at bit rates as low as 64 kbps
=
80 kbps, depending on the assignment of
