## 5 Performance Evaluation
### Imperceptibility and Payload Capacity  
The test of each audio signal was repeated 10 times, so it takes 200 experiments to test all the audio signals. Based on the principle of watermark embedding in Section 3, one-bit watermark can be embedded for each audio fragment. Since the length of the audio fragment is 256, the payload capacity of this algorithm is 44,100/256 = 172.27 bps. The average results about the SNR of the audio signal, the NC and BER of the extracted watermark and the payload capacity are listed in Table 1. The experimental results showed that the payload capacity of the algorithm is the same as that of paper [25], higher than that of paper [4; 12], and far higher than that of paper [16; 19]. The average SNR of this proposed algorithm is 23.49 dB, which is higher than that in papers [12; 16; 25] but not paper [19], while the payload capacity of this proposed algorithm is five times that of the paper [19]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Items** & **Proposed** & **Paper [4]** & **Paper [16]** & **Paper [25]** & **Paper [12]** & **Paper [19]** \\ \hline SNR (dB) & 23.49 & N/A & 21.37 & 18.42 & 20.32 & 26.79 \\ Capacity(bps) & 172.27 & 125 & 43.07 & 172.27 & 139.97 & 34.14 \\ NC & 1 & N/A & N/A & N/A & N/A & 1 \\ BER (\%) & 0.00 & 0.00 & N/A & N/A & 0.12 & 0.00 \\ \hline \hline \end{tabular} Note that N/A means no report is found in the selected algorithm.  
\end{table} 
Table 1: Experimental results of the signal-to-noise ratio (SNR), normalized correlation (NC), bit error rate (BER) and payload capacity (no attack). Figure 4: Four binary images to be embedded into the carrier audio signals: (**a**) The first image with dimensions of 100 \(\times\) 96; (**b**) The second image with dimensions of 200 \(\times\) 50; (**c**) The third image with dimensions of 200 \(\times\) 50; (**d**) The fourth image with dimensions of 100 \(\times\) 100. * MP3 compression: applying MP3 compression with 64 kbps to the watermarked audio signal. * MP3 compression: applying MP3 compression with 128 kbps to the watermarked audio signal. * Re-sampling: dropping the sampling rate of the watermarked audio signal from 44,100 Hz to 22,050 Hz and then rose back to 44,100 Hz. * Re-quantization: quantizing the watermarked audio signal from 16-bit/sample to 8-bit/sample and then back to 16-bit/sample. * Echo addition: adding an echo signal with a delay of 50 ms and a decay of five percent to the watermarked audio signal. The extracted images and the average experimental results of NC are shown in Figures 7-10 respectively. Figure 10: The extracted pictures of the first image under different attacks: (**a**) Low-pass filtering, NC = 1; (**b**) Amplitude scaling by 0.8, NC = 1; (**c**) Amplitude scaling by 1.2, NC = 1; (**d**) Noise corruption (20 dB), NC = 0.9985; (**e**) Noise corruption with 30 dB, NC = 0.9991;(**f**) Noise corruption with 35 dB, NC = 0.9998;(**g**) MP3 compression with 64 kbps, NC = 0.9998; (**h**) MP3 compression with 128 kbps, NC = 1; (**i**) Re-sampling, NC = 0.9998; (**j**) Re-quantization, NC = 0.9990; (**k**) Echo addition, NC = 1; (**l**) no attack, NC = 1. Figure 9: The extracted pictures of the second image under different attacks: (**a**) Low-pass filtering, NC = 1; (**b**) Amplitude scaling by 0.8, NC = 1; (**c**) Amplitude scaling by 1.2, NC = 1; (**d**) Noise corruption (20 dB), NC = 0.9911; (**e**) Noise corruption with 30 dB, NC = 0.9975; (**f**) Noise corruption with 35 dB, NC = 0.9992; (**g**) MP3 compression with 64 kbps, NC = 0.9998; (**h**) MP3 compression with 128 kbps, NC = 1; (**i**) Re-sampling, NC = 1; (**j**) Re-quantization, NC = 0.9986; (**k**) Echo addition, NC = 0.9999; (**l**) no attack, NC = 1.