# Interpolating the Directional Room Impulse Response for Dynamic Spatial Audio Reproduction
## 4 Results and Analysis
### Comparative Analysis in the Great Hall
#### 4.2.2 Regular and Irregular Spacing, Row 9  
The next comparison chooses positions at row 9 (the rear of the great hall) to explore the effect of the source-microphone distance and the inter-microphone distance on the DRIR interpolation accuracy. The first case selects known DRIR points at 1 m either side of the interpolation point (purple circles of Figure 4b). Another case chooses the same listening point and left DRIR as case 1, but the right DRIR is 4 m away (black circles of Figure 4b). DRIR interpolation results for these two cases in the real-world and simulated great halls are provided in the first two rows of Figures 10 and 11, respectively. Firstly, we investigate the effects of the source-to-microphone distance on DOA and TOA estimation accuracy. By comparing the top subplot (row 9 with 1 m spacing) in Figures 10 and 11 with the top one in Figures 8 and 9 (Row 4 with 1 m spacing), respectively, it can be found that the DOA and TOA errors in row 9 are overall smaller than those for Row 4. Note that the proposed method shows the most consistent results in these rows in the real-world great hall. Although its error increases from row 9 to row 4, the change is not large. These results demonstrate that the further the listening position and known DRIR positions are from the source, the more accurate the DRIR interpolation will be. This argument generally holds for all the three comparative approaches. A possible explanation for this is that while row 9 is further from the source, the angular separation between the two known DRIR points used in the interpolation is smaller than that for row 4. Figure 8: Bar charts comparing the accuracy of the [PERSON]’s method in 2009, the [PERSON]’s method in 2016, and the proposed DRIR interpolation algorithm in the real-world great hall arranged as shown in Figure 4b, including: (**a**) the error of azimuth and elevation; (**b**) the error of TOA. All errors are calculated as the absolute difference between the interpolated signal and the ground truth for a reference-to-known-point spacing of 1 m, 2 m, and 3 m (from top to bottom in each subplot) in row 4. In Figure 11, the reduction of errors in the simulated great hall because of larger source-microphone distances is not as apparent as in Figure 10. Looking at the azimuth error in both row 9 (Figure 11) and row 4 (Figure 9), the direct sound and the first two specular reflections in row 9 are all accurate, and the [PERSON]'s and [PERSON]'s methods both obtain an error of nearly five degrees. The proposed algorithm presents nearly no error in these two rows with 1 m spacing. For the fifth peak, row 9 results are smaller, but at the sixth peak, row 9 errors are much larger than that in row 4. In Figure 11a, row 9 elevation results are smaller than that in row 4 in Figure 9a but are not obvious. Only in Figure 11b are the TOA errors for row 9 significantly smaller than that in row 4 in Figure 9b. Therefore, the proposed method and two representative DRIR interpolation approaches all perform better for larger source-microphone distances. Analyzing results for irregular spacing for row 9 in Figure 10, it can be seen that the two cases in row 9 (regular vs. irregular spacing) have very similar results in the real-world great hall for all methods. For the same positions in the simulated great hall in Figure 11, the elevation and TOA errors for the proposed method and the [PERSON]'s method are also similar for both cases (regular vs. irregular spacing). In contrast, the results for the [PERSON]'s approach show more variation for these two cases (e.g., see elevation errors of peaks 4 and 5 in Figure 11a and TOA errors of peaks 4 and 5 of Figure 11b).