# Automatic Spatial Audio Scene Classification in Binaural Recordings of Music +
## 3 Results
### Principal Component Analysis  
In order to further investigate the relations between the BRIR sets, the test dataset was examined using principal component analysis (PCA). According to the [PERSON] overall measure of sampling adequacy (0.8) and [PERSON]'s test of sphericity (chi squared tending to infinity, df = 946,000, \(p=0\)), the data were factorizable. The standard PCA method, based on eigenvalue decomposition, was utilized in this study. The obtained results are illustrated in Figures 5 and 6. The first two principal \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reverberation** & **RT60** & **BRIRs Used for** & **BRIRs Used for** & **Test Accuracy (\%)** \\
**Time** & **RT60** & **Training** & **Testing** & **Test Accuracy (\%)** \\ \hline Short & 0.17\(-\)0.31 s & sbs, thkxr1, calypso, & & thkxr7, tuburo250 & 65.4 (59.0, 71.4) \\ Medium & 0.7\(-\)1.0 s & thksbs, tvtui & tvtui2 & 51.7 (42.4, 60.9) \\ Long & 1.8\(-\)2.1 s & thklbs & mair & 40.0 (31.2, 49.3) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Accuracy of classification (%) obtained for models trained and tested using the recordings synthesized with BRIR sets of similar reverberation time. Numbers in brackets represent 95% confidence intervals. Figure 4: Confusion matrices obtained for the best three models in experiment 2: (**a**) tvtui2; (**b**) tuburo310; and (**c**) labtui. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**No.** & **BRIR Set Left-Out** & **Training Accuracy (\%)** & **Testing Accuracy (\%)** \\ \hline
1 & sbs & 80.8 & 44.2 (35.1, 53.5) \\
2 & mair & 80.8 & 56.7 (47.3, 65.7) \\
3 & thkxr1 & 81.5 & 45.8 (36.7, 55.2) \\
4 & thkxr7 & 80.6 & 65.0 (55.8, 73.5) \\
5 & thksbs & 81.1 & 65.0 (55.8, 73.5) \\
6 & thklbs & 82.0 & 50.0 (40.7, 59.3) \\
7 & calypso & 80.6 & 37.5 (28.8, 46.8) \\
8 & tvtui & 80.8 & 55.8 (46.5, 64.9) \\
9 & tvtui2 & 81.1 & 79.2 (70.8, 86.0) \\
10 & labtui & 81.7 & 65.8 (56.6, 74.2) \\
11 & rehabtui & 81.9 & 35.8 (27.3, 45.1) \\
12 & tuburo250 & 81.6 & 64.2 (54.9, 72.7) \\
13 & tuburo310 & 81.0 & 73.3 (64.5, 81.0) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: The results of the leave-one-BRIR-out validation. Numbers in brackets represent 95% confidence intervals. component dimensions accounted for 10.5% and 7.4% of the total variance, respectively. For clarity, the most prominent 25 variables were shown in Figures 5a and 6a. According to Figure 5a, both dimensions predominantly represented the spectral metrics. The first dimension was mainly affected by spectral roll-off, whereas the second dimension was primarily influenced by centroid, crest, flux, and flatness. According to Figure 5b, the stimuli synthesized using all BRIR sets were similar to each other (significant overlap of the BRIR scores). Figure 5: Results of the principle component analysis (PCA) for dimensions 1 and 2: (**a**) variable plot; (**b**) audio recordings. Ellipses represent a concentration of the scores for each BRIR set with 95% confidence boundaries around group means. Figure 6: Results of the PCA for dimensions 3 and 4: (**a**) variable plot; (**b**) audio recordings. Ellipses represent a concentration of the scores for each BRIR set with 95% confidence boundaries around group means. Principal component dimensions 3 and 4 accounted for 5.9% and 4.8% of the total variance, respectively (Figure 6a). In contrast to the previously discussed results, the calypso BRIR set appeared to be distinctively different compared to the remaining BRIR sets (Figure 6b). This difference was caused by the spatial characteristics of that BRIR set, since dimension 3 was predominantly affected by the binaural cues, such as IC and ITD. Dimension 4 was mainly affected by the spectral features (high frequency content and spectral spread) and, to an extent, by the RMS-based metric. The above observation, regarding the \"outlying\" characteristics of the stimuli synthesized using the calypso BRIR set, was in line with the results of the informal listening tests described earlier in Section 2.2.2.