# Effective Dereverberation with a Lower Complexity at Presence of the Noise
## 4 Experiments and Evaluation
### Analysis and Comparison of the Test Results
#### 4.3.3 Performance Comparison with Reference Methods  
Two proposed dereverberation algorithms and two reference methods are evaluated for different _SNR_ and \(T_{60}\). Six kinds of reverberation time are considered at four _SNR_ conditions. Tables 1-4 show the results of performance evaluation for the unprocessed speech. It is worth noting that the PESQ value of the unprocessed signal increases with the increase in the reverberation time. This is because in the case of lower input _SNR_, compared with low reverberation, the high reverberation can resist more noise, so that the speech is not submerged into the annoying noise. Under the condition of high SNR, the performance of the proposed method is not very good compared with the reference methods, and especially worse than the WPE. The reason is that under the condition of high SNR, the speech distortion caused by the noise is far less than that caused by the reverberation. Meanwhile, WPE can remove reverberation well and improve the speech quality greatly. Under the condition of low reverberation, the ISCLP shows better results and the WPE shows worse results, because WPE has no denoising ability. Under the condition of low SNR, it can be found that the results of the PESQ, STOI, and fwSegSNR of the proposed method are higher than these two reference methods in most cases, and the result of STOI is significantly improved especially in the case of \(-5\) dB, whereas the low-complexity version of the proposed method (called proposed-kron) is similar to the proposed method. As shown in Tables 1 and 2, the fwSegSNR is also significantly improved in all cases. In the results for CD, the WPE shows the best performance. As the distortion measurement of the speech, the results of CD show that both the proposed method and ISCLP introduce the distortion, and the ISCLP causes more distortion. The distortion is due to the PSD error of the desired signal in the Kalman filtering. The GSC-based beamforming used in the ISCLP causes speech distortion because of the inaccurate RETF. For the SIR, the ISCLP shows the best effect. The ISCLP reduces much of the interference at the cost of introducing more speech distortion. The proposed method balances the speech distortion and interference reduction. Within a certain distortion range, the proposed method eliminates more interference signal than the WPE. The proposed-kron method also shows good results with low complexity. From the discussion above, the proposed method shows better performance under the condition of low SNR and high reverberation. In future work, the problem of speech distortion in the proposed method needs to be improved. \begin{table}
\begin{tabular}{c c c c c c c} \hline \(T_{60}\) (ms) & 100 & 400 & 500 & 600 & 700 & 800 \\ \hline \multicolumn{8}{c}{PESQ} \\ \hline unprocessed & 1.12 & 1.51 & 1.56 & 1.58 & 1.61 & 1.62 \\ ISCLP & **1.50** & 1.58 & 1.63 & 1.66 & 1.69 & 1.71 \\ WPE & 1.12 & 1.47 & 1.52 & 1.53 & 1.54 & 1.56 \\ proposed & 1.20 & 1.66 & 1.72 & **1.77** & **1.78** & **1.79** \\ proposed-kron & 1.19 & **1.68** & **1.75** & **1.77** & **1.78** & **1.79** \\ \hline \multicolumn{8}{c}{STOI} \\ \hline unprocessed & 0.51 & 0.58 & 0.58 & 0.58 & 0.56 & 0.56 \\ ISCLP & **0.59** & 0.57 & 0.57 & 0.57 & 0.57 & 0.57 \\ WPE & 0.50 & 0.57 & 0.57 & 0.58 & 0.59 & 0.59 \\ proposed & 0.54 & **0.61** & **0.62** & **0.62** & **0.62** & **0.62** \\ proposed-kron & 0.54 & **0.61** & **0.62** & **0.62** & **0.62** & 0.61 \\ \hline \end{tabular}
\end{table} 
Table 1: Comparison of the test results at \(-5\) dB for babble noise. (The bold in the table indicates the best result).