## 5 Conclusions  
The purpose of this experiment was to find out the average perceptual thresholds of four BRIR parameters to represent the generic thresholds on perceptual reverberation, and determine whether these parameters have significant impact on perceptual reverberation. The measurement of these thresholds lays a foundation for the realisation of more idealised artificial reverberation algorithms, which can be applied in AR scenarios to create more plausible reverberation effects. This research makes the following conclusion through the measurement and the analysis for ITDG, FER, RER and LR:  
* The average thresholds of RER removal are 15.81 ms, 17.49 ms and 18.18 ms corresponding to 0.31 s, 0.91 s and 1.51 s reverberation time, respectively. The average thresholds of ITDG extension are 18.37 ms, 25.21 ms and 30.75 ms. The reverse removal of ERs and extension of ITDG causes relatively obvious effects on reverberation perception of speech audio, so RER and ITDG should be focused on when designing artificial reverberation algorithms. * The average thresholds of FER removal are 27.68 ms, 34.33 ms and 34.6 ms, respectively, for each reverberation time. Generally, subjects were less sensitive to FER removal; therefore, FER is less of a concern when designing a reverberation algorithms. * The average thresholds of LR removal are 435.52 ms, 771.16 ms and 1276.9 ms, respectively. LR removal has a small influence on perceptual reverberation, so when achieving an artificial reverberation algorithm, small changes in LR may not be significant. * The ANOVA test shows that reverberation time does not affect the thresholds of RER removal, ITDG extension and FER removal on perceptual reverberation, but the thresholds of LR removal on perceptual reverberation are impacted by reverberation time. Early reflections are achieved by finite impulse response (FIR) delay lines and late reverberation by infinite impulse response (IIR) filters. Whilst focusing on hybrid FIR and IIR filters would certainly theoretically lead to more accuracy, exploiting perceptual sensitivity to reverberation could reduce computational resources for algorithm design. Based on the experimental findings, it appears that LR removal has a smaller effect on perceptual reverberation, and although FER does not affect perceptual reverberation as much as RER, overall ER can have an obvious effect on perceptual reverberation. ITDG can also have a significant effect on perceptual reverberation. In order to balance reverberation accuracy and algorithmic efficiency, perceptually motivated reverberation algorithms should focus on ERs and ITDG. When designing reverberation algorithms, early reflections are achieved by means of FIR delay lines. More finite impulse responses require more computational cost, so the number of finite impulse responses can be minimised, depending on the measured threshold, without affecting reverberation perception. ITDG has a large impact on perceptual reverberation, so controlling the time period between direct sound and early reflections as accurately as possible when designing a reverberation algorithm can improve efficiency in the design. **Author Contributions:** Conceptualisation, H.M. and G.K.; methodology, H.M., G.K. and H.D. ; software, H.M.; validation, H.M., G.K. and H.D. ; formal analysis, H.M., G.K. and H.D. ; investigation, H.M.; resources, H.M., G.K. and H.D. ; data curation, H.M.; writing--original draft preparation, H.M.; writing--review and editing, G.K. and H.D. ; visualisation, H.M.; supervision, G.K. and H.D. ; project administration, H.M. All authors have read and agreed to the published version of the manuscript. **Funding:** This research was supported by the Engineering and Physical Sciences Research Council IAA project \"MINERVA: Musical Interactions in Networked Experiences using Real-time Virtual Audio\".