## 4 Experimental Results
### Waveform Comparison  
The goal of the proposed methods is to achieve packet loss concealment, so this experiment selects the time domain waveform to compare the variation of speech signal in the time for the different PLC methods.  
In order to intuitively show the effect of the proposed PLC methods, 5% packet loss rate is taken as an example. The DNN-based PLC method and the proposed method based on the DNN and GLA are first compared. Figure 9 shows the proposed PLC waveform with time domain phase correction. As shown in Figure 9, although the DNN-based PLC method produces the concealed waveform in the loss frame, the inaccurate phase estimation leads to the phenomenon of waveform cancellation. In order to show the influence of inaccurate phase estimation on the PLC, the waveform (c) is obtained by combining the real phase with the log-power spectrum predicted by DNN. We can find that there is an excellent concealment using the real phase.  
In Figure 9c, although the GLA used for phase correction produces a slightly better waveform than the DNN\(-\)PLC, there is still a big gap. In addition, in Figure 9c, it can be clearly seen that the peak of the waveform generated by the DNN+GLA\(-\)PLC method is in a \"dislocation\" state. This is also due to the poor learning effect of the DNN on the phase spectrum, which leads to a high degree of distortion in its phase spectrum estimation. For the WSOLA\(-\)PLC method shown in Figure 9d, the amplitude of the lost frame is obviously distorted, which also shows the limitation of the WSOLA method. Although the pitch period is kept continuous, the change of the amplitude will make the listening experience significantly worse because the human ear is more sensitive to amplitude than phase, whereas the proposed DNN+WSOLA\(-\)PLC method shown in Figure 9e nearly maintains the same amplitude of waveform before and after packet loss. In addition, the consistency of periodic characteristics of the waveform is kept well before and after packet loss.  
As shown in Figure 10, four coordinate points are marked. The distance of the first two peaks indicates the period of waveform without packet loss, whereas the distance between the last two peaks, respectively, represents the periods of the concealed waveforms by WSOLA\(-\)PLC and DNN+WSOLA\(-\)PLC. We can observe that the proposed method can preserve periodic characteristics of speech signal and achieve better phase concealment effect.  
The waveforms are also compared in Figure 11 in the case of 30% packet loss rate. We can find that DNN\(-\)PLC has the phenomenon of signal cancellation due to the inaccurate phase. For the proposed DNN+GLA\(-\)PLC, since the phase spectrum is corrected to some extent by the amplitude spectrum, the concealed waveform is more similar to the original one. However, the performance of the PLC is still not satisfactory. In the case of continuous packet loss, the amplitude distortion caused by WSOLA\(-\)PLC is more obvious, because only a Hanning window is used to smooth the amplitude. For the proposed DNN+WSOLA\(-\)PLC, when multiple packets are lost continuously, the periodic characteristics of speech signal are still well preserved and the phase is continuous. At the same time, combined with the prediction of the DNN for the lost amplitude information, a concealed waveform is well obtained.  
As a result of waveform comparison, the proposed DNN+WSOLA\(-\)PLC method can achieve better packet loss concealment in both amplitude and phase information, even at a higher packet loss rate.  
Figure 9: Waveform comparison: (**a**) 5% packet loss; (**b**) DNN\(-\)PLC; (**c**) DNN+GLA\(-\)PLC; (**d**) WSOLA\(-\)PLC; (**e**) DNN+WSOLA\(-\)PLC; (**f**) no packet loss.