# Exploring the Effectiveness of the Phase Features on Double Compressed AMR Speech Detection
## 7 Experimental Results
The results reveal that combining deep features learned by the parallel LSTM network from two different sources (magnitude and phase spectrum) considerably improves DC speech detection rates compared to using single CosPhase features (Table 6) for almost all BR1-BR2 combinations. For instance, while a 56.35% detection rate is achieved when BR1 = 6.6 kbps and BR2 = 8.85 kbps using stand-alone CosPhase features, employing the parallel LSTM network, which combines two deep features, increases the \begin{table}
\begin{tabular}{l c c c c c c c c c} \hline \hline  & & & \multicolumn{8}{c}{BR2 (kbps)} \\  & & 6.6 & 8.85 & 12.65 & 14.25 & 15.85 & 18.25 & 19.85 & 23.05 & 23.85 \\ \hline  & 6.6 & 62.90 & 56.35 & 85.35 & 88.28 & 89.95 & 93.61 & 94.81 & 97.07 & 94.03 \\  & 8.85 & 65.12 & 57.23 & 86.08 & 89.56 & 92.19 & 95.75 & 96.48 & 98.49 & 95.75 \\  & 12.65 & 65.96 & 55.35 & 84.56 & 89.37 & 90.71 & 95.14 & 96.19 & 98.03 & 95.60 \\  & 14.25 & 66.40 & 56.77 & 86.35 & 88.26 & 89.95 & 95.41 & 96.61 & 98.22 & 95.46 \\ BR1 & 15.85 & 66.54 & 57.30 & 85.69 & 89.58 & 90.96 & 94.70 & 95.92 & 98.41 & 95.27 \\ (kbps) & 18.25 & 66.40 & 57.17 & 88.45 & 90.56 & 91.42 & 95.20 & 96.35 & 98.32 & 95.64 \\  & 19.85 & 65.96 & 58.24 & 86.98 & 90.08 & 91.50 & 95.35 & 96.31 & 98.32 & 95.64 \\  & 23.05 & 68.11 & 59.22 & 89.24 & 91.96 & 92.63 & 95.79 & 96.82 & 98.32 & 95.96 \\  & 23.85 & 71.90 & 70.10 & 88.47 & 92.00 & 93.22 & 96.82 & 97.99 & 99.26 & 94.60 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Detection rates (TPR in %) for DC AMR-WB speech using CosPhase features and the baseline LSTM network. The underlined entries in the table indicate the BR1-BR2 combinations with higher detection rates in comparison to results obtained using spectrogram features in Table 5. \begin{table}
\begin{tabular}{l c c c c c c c c c c} \hline \hline  & & & \multicolumn{8}{c}{BR2 (kbps)} \\  & & 6.6 & 8.85 & 12.65 & 14.25 & 15.85 & 18.25 & 19.85 & 23.05 & 23.85 \\ \hline  & 6.6 & 92.76 & 95.14 & 94.72 & 95.25 & 94.87 & 94.56 & 94.99 & 95.41 & 95.14 \\  & 8.85 & 93.09 & 92.53 & 93.93 & 94.03 & 93.17 & 94.18 & 93.87 & 93.97 & 96.06 \\  & 12.65 & 89.68 & 89.12 & 86.31 & 86.46 & 84.64 & 85.81 & 86.19 & 87.48 & 90.56 \\  & 14.25 & 89.43 & 88.91 & 86.50 & 85.46 & 84.03 & 84.62 & 85.83 & 85.64 & 89.49 \\ BR1 & 15.85 & 89.30 & 87.63 & 85.31 & 85.39 & 83.26 & 84.33 & 85.41 & 85.83 & 89.18 \\ (kbps) & 18.25 & 88.30 & 87.09 & 84.16 & 83.91 & 81.35 & 82.90 & 83.22 & 83.32 & 88.13 \\  & 19.85 & 87.59 & 87.02 & 84.03 & 83.41 & 80.94 & 82.25 & 82.38 & 83.34 & 87.63 \\  & 23.05 & 86.50 & 85.87 & 82.25 & 81.63 & 79.89 & 80.87 & 81.19 & 81.71 & 86.92 \\  & 23.85 & 79.81 & 78.13 & 73.55 & 73.87 & 70.02 & 71.46 & 72.17 & 71.92 & 73.20 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Detection rates (TPR in %) for DC AMR-WB speech using spectrogram features and the baseline LSTM network. detection rate to 74.64%, representing an approximately 32% performance improvement. The only exception where the parallel LSTM results are slightly lower than the phase spectrum features is when BR2 = 23.85 kbps. However, the performance difference between the two systems (parallel LSTM and LSTM with phase spectrum) is not considerably large. Similarly, the parallel LSTM outperforms the spectrogram features for almost every second compression bit rate, except for 6.6 and 8.85 kbps. Interestingly, when the BR2 value is either 6.6 kbps or 8.85 kbps, the spectrogram features yield better DC speech detection rates than the phase spectrum features or the parallel LSTM system. This observation suggests that magnitude spectrum features are more effective when the BR2 value is very low. With the exception of these two very low BR2 values, the parallel LSTM results are advantageous over stand-alone spectrogram features.