## 6 Results
### Individual vs. Generalized HRTF Tests  
This section presents the results of another form of the HRTF-independent tests. In contrast to the tests described in the previous section, a different strategy for creating data folds was pursued. The remaining aspects of the methodology were identical as before, and their description is omitted here. Instead of using four data folds as in the previous experiment, only two data folds were considered in the study. For the first data fold, the model was developed with the excerpts synthesized using the artificial (generalized) HRTFs, and then it was tested on the excerpts obtained with the human (individual) HRTFs. For the second data fold, the procedure was reversed. Namely, the model was developed  
Figure 7: Mean classification accuracy scores obtained under HRTF-independent tests. Error bars represent standard deviations. exploiting the excerpts obtained with the human HRTFs and tested with the excerpts convolved with the artificial HRTFs (as before, for both folds, the development and test sets were unique in terms of the music content). Recall that HRTFs used in this study were selected in such a way that two corpora were obtained using human heads (HUTUBS and SADIE), whereas the remaining two ones were measured with the artificial heads (TH-Koln and TU-Berlin). Consequently, the proportion between the human and artificial HRTFs was balanced. For consistency with the previous section, the data folds used in this experiment are outlined in Table 8.  
The obtained results are illustrated in Figure 9. The maximum average scores are similar to the ones described above, ranging between 70% and 80% (cf. Figure 7). Similar \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ensemble Location** & **Precision** & **Recall** & **\(F1\)-Score** \\ \hline front & 86.6 (4.5) & 59.4 (7.2) & 70.3 (5.8) \\ back & 60.3 (3.3) & 79.3 (2.8) & 68.4 (1.7) \\ up & 80.0 (2.6) & 50.0 (2.8) & 61.5 (3.3) \\ down & 64.1 (2.2) & 87.7 (2.5) & 74.0 (1.4) \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Classification results for the ensemble width of \(\pm\)60\({}^{\circ}\) for SADIE corpus. Numbers in brackets represent standard deviations. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Ensemble Location** & **Precision** & **Recall** & **\(F1\)-Score** \\ \hline front & 85.8 (3.4) & 52.6 (5.4) & 65.0 (4.0) \\ back & 54.2 (2.7) & 72.1 (4.5) & 61.8 (2.1) \\ up & 81.7 (3.1) & 22.9 (5.1) & 35.5 (6.1) \\ down & 54.1 (3.5) & 95.3 (2.2) & 68.8 (2.5) \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Classification results for the ensemble width of \(\pm\)60\({}^{\circ}\) for TH-Koln corpus. Numbers in brackets represent standard deviations. Figure 8: Example confusion matrices obtained under the HRTF-independent tests: (**a**) \(\pm\)60\({}^{\circ}\) SADIE, (**b**) \(\pm\)60\({}^{\circ}\) TU-Berlin, (**c**) \(\pm\)60\({}^{\circ}\) TH-Koln, (**d**) \(\pm\)90\({}^{\circ}\) SADIE, (**e**) \(\pm\)90\({}^{\circ}\) TU-Berlin, (**f**) \(\pm\)90\({}^{\circ}\) TH-Koln. to the results seen in the previous section, the minimum scores are observed for the widest ensembles (\(\pm\)90\({}^{\circ}\)), being equal to approximately 50%. However, in contrast to the results discussed before, the maximum accuracy scores are not seen for the narrowest ensembles but for the ensembles having the widths of \(\pm\)30\({}^{\circ}\) and \(\pm\)45\({}^{\circ}\), respectively, depending on the type of heads used for testing. Interestingly, while the two curves presented in Figure 9 show a relatively high correlation (overlap) for the ensemble widths between \(\pm\)45\({}^{\circ}\) and \(\pm\)90\({}^{\circ}\), there are noticeable differences between the results for the two narrowest ensembles (\(\pm\)15\({}^{\circ}\) and \(\pm\)30\({}^{\circ}\)). These differences are statistically significant at \(p<\) 0.001 according to the \(t\)-test.