# Secure Speech Content Based on Scrambling and Adaptive Hiding
## 4 Method Implementation and Validation
### Comparison with State-of-the-Art Methods  
In this section, we compare the performance of our proposal with some state-of-the-art methods in the field of speech steganography. Table 1 shows the results, \(h\) being the host signal, \(s\) the stego signal, \(m\) the secret message, \(r\) the recovered message, \(Corr(.,.)\) the correlation coefficient, \(PSNR(.,.)\) the Peak Signal-to-Noise Ratio, \(BER(.,.)\) the Bit Error Rate, and \(HC\) the hiding capacity.  
Firstly, every parameter is explained, as follows:  
\(Corr\) is the square root of \(PCC\) (Section 4.3). Unlike \(PCC\), \(Corr\) can be positive or negative. If the value is positive it means direct correlation, otherwise, it means opposite correlation. Higher \(Corr\) means more similarity between the signals.  
\(PSNR\) measures the difference between the host signal, \(h\), and the stego signal, \(s\). Higher \(PSNR\) means that the stego signal is more similar to the host signal.  
\[PSNR=10\log_{10}\frac{\sum_{i=1}^{N}h\left(i\right)^{2}}{\sum_{i=1}^{N}\left[h \left(i\right)-s\left(i\right)\right]^{2}} \tag{7}\]  
\(BER\) calculates the ratio of the differences (bit to bit) between the message, \(m\), and the recovered message, \(r\). Higher \(BER\) means that the hiding process is reversible and better.  
\[BER=\frac{1}{L}\sum_{i=1}^{L}\begin{cases}1,&m(i)\
eq r(i)\\ 0,&m(i)=r(i)\end{cases} \tag{8}\]  
Hiding Capacity can be calculated in many ways. For the purpose of this paper, it is the ratio of the size of the secret message by the size of the host signal. Higher \(HC\) means a better performance of the system in terms of its payload.  
According to Table 1, the greatest strength of our proposal is the simultaneous fulfilment of security requirements, the quality of the signal stego, and quality of the recovered signal. Our system provides very high security through a very large key space; high values of \(HC\), high values of \(Corr(h,s)\) as well as \(Cor(m,r)\). In terms of \(PSNR\), our proposal is the worst, but, it is important to remark that this parameter is not only sensitive to distortion of the signal, but to changes of the amplitude of the signal. It means that the \(PSNR\) between a signal and its amplified version is not infinite, although both signals have the same content. For that reason, there are more confident in the results of similarity in terms of correlation.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Reference** & **[20]** & **[21]** & **[22]** & **[23]** & **Ours** \\ \hline \multirow{3}{*}{**Method**} & **Hermite Transform** & **RSA + 2-bit** & **LSB** & **Variable Low Bit** & **Adaptive** \\  & **(HT) and Threshold** & **LSB** & **Multi-Threshold** & **Coding (Up** & **Scrambling** \\  & & & **Based Criterion** & **To 3-Bit LSB)** & **+ Adaptive LSB** \\ \hline \(Corr(h,s)\) & 0.988 & NR & NR & NR & 0.992 \\ \(PSNR(h,s)\) & 32.7 dB & 34.27 dB & NR & 47 dB & 23.61 dB \\ \(Corr(m,r)\) & 0.961 & NR & NR & NR & 0.974 \\ \(BER(m,r)\) & NR & 18\% & NR & 24\% & NR \\ \(HC\) & 0.5 & \(<\)0.125 & \([0.10.28]\) & \(<\)0.13 & \(>\)0.5 \\ Key space & NR & NR & 280 & NR & L! \\ \hline \hline \end{tabular}
\end{table}
Table 1: Performance of some state-of-the-art methods (NR means Not Reported). \(h\) being the host signal, \(s\) the stego signal, \(m\) the secret message, \(r\) the recovered message, \(Corr(.,.)\) the correlation coefficient, \(PSNR(.,.)\) the Peak Signal-to-Noise Ratio, \(BER(.,.)\) the Bit Error Rate, and \(HC\) the hiding capacity.