# Head-Related Transfer Functions for Dynamic Listeners in Virtual Reality
## 6 Discussion
### Dynamic Results
The lowest static and dynamic localization errors for virtual sounds in recent studies have resulted from experiments conducted with floating headphones, where in-ear headphones are mounted in front of the open ear canal entrance and individual headphone calibration is performed at the beginning of each experiment [9; 12], using a procedure originally described in [43]. This procedure is different from the diffuse-field calibration performed in the present experiments and suggested in the previous literature [4; 30]. Although yielding accurate localization results in the absence of visuals, the individual calibration procedure is laborious and unfeasible with current headphone technology for the general public. The lack of differences between generic and individual HRTFs in this study in a 6-DoF VR context add evidence to the cross-modal integration and adaptation effects on sound localization, possibly circumventing the need for high fidelity individual spatial cues delivery. The preference in timbre in favor of the generic set is in agreement with previous research [16], where the effect of higher quality microphones in the generic binaural head was suspected to be one reason for the higher perceived timbre fidelity. In the study at hand, defining the _No HRTF_ condition as the timbre reference may cause potential confusion in the participants since any of the HRTF conditions is spatially different from the reference. Moreover, the HRTFs cause timbre coloration by definition, making the comparison to a non-filtered stimulus unfair. It might be argued that the stronger localization cues the HRTF can convey, the more different the timbre will be from a non-spatial stimulus. In informal discussions with the participants, all of them had understood the goal of comparing the non-spatial timbre with a spatialized version, requiring a certain degree of mental simulation of how a real sound source should sound like if placed in front of the listener. The timbre results should only be viewed together with the localization and overall quality results to attain an accurate picture of the quality of the HRTF sets. The overall quality results support our findings in localization and timbre: the individual and generic HRTF sets are perceived to be highly similar in quality. Here, the participants were allowed to focus on any aspect of the auditory experience while keeping in mind the boundary conditions set by the visuals and motor actions. The scenes were also more complicated than the previously presented scenes in this experiment, both in the number of audio objects and their content. Still, it may be argued that the employed scenes were far from a scene that might be experienced in the real world. In a real scene or a more realistic virtual scene, there would most likely be multiple competing audio objects active simultaneously and blending into a holistic perception of a soundscape. Then, given a visual scene to match the soundscape, the contribution of any individual audio object's auditory localizability to the overall experience would most likely be small. The experiments in this study were conducted in anechoic conditions to highlight the impact of HRTF fidelity on localizability and overall audio quality, representing the worst-case scenario for virtual audio. Based on previous literature, we may assume that adding early reflections and reverberation would further reduce the prominence of differences between individual and generic HRTF sets since these cues affect the spatial impression and externalization [8,44]. Furthermore, more realistic acoustic conditions would ease the integration of visual and auditory environments by reducing the room divergence effect [45], potentially reinforcing the adaptation to generic localization cues. In summary, our results showed significant objective differences between three HRTF sets, but minimal perceptual differences in dynamic 6-DoF VR scenes.