# Multimode Tree-Coding of Speech with Pre-/Post-Weighting +
## 13 Performance Comparisons of MMT-WP with Other Codecs  
Table 7 shows the PESQ, average bitrate, algorithmic delay, and computational complexity comparison of the MMT-WP codec with AMR-NB and G.727 [3]. We see that the MMT-WP codec can produce the same output speech quality as G.727 but at much lower bit rates. Furthermore, the MMT-WP codec has much lower complexity and much lower delay than AMR-NB while producing the same output speech quality, albeit at higher bit rates. Table 7 shows the range of PESQ-MOS, bitrate, delay, and computational complexity over the utterances examined, but a closer examination can indicate where the variations are \begin{table}
\begin{tabular}{c c} \hline \hline
**Sequence** & **Complexity of MMT-WP** \\ \hline \hline lathe & 2.63 \\ we were away & 4.73 \\ af1s01 & 1.49 \\ af1s02 & 1.61 \\ af1s03 & 1.91 \\ am1s01 & 1.31 \\ am1s02 & 1.34 \\ am1s03 & 1.45 \\ \hline Average & 2.06 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Estimated computational complexity (WMOPS) for narrowband sequences. \begin{table}
\begin{tabular}{l c c} \hline \hline
**Process** & **Computational Complexity (WMOPS)** & **Mode** \\ \hline Mode Decision in Encoder & 0.0178 & V, UV, ON, H, S \\ Pre-weighting filter in Encoder & 0.208 & V, ON \\ Tree Coder in Encoder & 1.385 & V, UV, ON, H \\ Pitch Predictor in Encoder & 1.1919 & V \\ Silence Encoding & 0.0008 & S \\ G.727 Decoder & 0.625 & V, UV, ON, H \\ Pitch Predictor in Decoder & 1.1919 & V \\ Post-weighting filter in Decoder & 0.208 & V, ON \\ Silence Decoding & 0.07056 & S \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Estimated computational complexity (WMOPS) of MMT-WPfrom. Operational rate distortion functions allow a more detailed performance comparison of possibly competitive voice codeces [41]. Figures 7-14 show PESQ and average bitrate of different speech codecs on 8 clean English sequences described in Table 1.  
Compared to AMR-NB, the PESQs of MMT-WP with weighting and pitch predictor using 3 bits/sample for Voiced and Onset (the highest bitrate of MMT) are comparable with the PESQs of AMR-NB at 12.2 kbps (the highest bitrate of AMR-NB). Even though the average bitrate of MMT-WP is 0.25-1.5 bit/sample higher than that of AMR-NB, the delay and computational complexity of MMT are significantly lower than those of AMR-NB. Furthermore, the algorithmic delay of MMT-WP is 6.125 msec while that of AMR-NB is 25 msec. Thus, the delay of MMT-WP is about a quarter of AMR-NB. The worst computational complexity of MMT-WP with weighting and pitch predictor is 4.83 WMOPS while the worst computational complexity of AMR-NB is 16.7 WMOPS. Therefore, MMT-WP saves about 70% in computational complexity. Referring to Figure 8 and comparing MMT-WP to G.727 for the sequence \"we were away,\" the PESQ for G.727 at 16 kbps is 2.513 while the PESQ for MMT with weighting and pitch predictor at 24 kbps is 4.012. Moreover, the PESQ for G.727 at 32 kbps is 3.66, which is lower than the PESQ for MMT-WP at 32 kbps. This shows that MMT with weighting and pitch predictor saves about 1 bit/sample when PESQ is comparable with G.727. Analyzing Figures 7 and 8 to compare MMT-WP with AMR-NB, we see that there is a relatively constant gap of just under 1 bit/sample between MMT-WP and AMR-NB for \"lathe\" with the same PESQ-MOS values, and this gap widens to 1.5 to almost 2 bits/sample for \"we were away\" since the MMT-WP loses any rate reduction produced by VAD/CNG because \"we were away\" is all voiced. Comparing results in Figures 9-14, where the first three figures are for female speakers and the latter three are for male speakers, we can see some further trends. First, it is evident \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Attribute** & **MMT-WP V3, UV:2** & **AMR-NB 12.2 kbps** & **G.727 24 kbps** \\ \hline PESQ & 3.638–4.012 & 3.602–4.136 & 3.243–3.814 \\ \hline bitrate (kbps) & 7.90–24.40 & 5.97–12.2 & 24 \\ \hline Delay (msec) & 6.125 & 25 & 0.125 \\ \hline Complexity (WMOPS) & 1.31–4.83 & 11.9–16.7 & 1.25 \\ \hline \hline \end{tabular}
\end{table}