# Head-Related Transfer Functions for Dynamic Listeners in Virtual Reality
## 5 Experiment II: Dynamic 6-DoF Virtual Reality
### Stimuli and Conditions  
Five conditions were created for each of the 6-DoF VR scenes based on the HRTF sets: _Measured, Modeled, Generic, Generic horizontal_, and _No HRTF_. The first three conditions were the same as in Experiment II. The _Generic horizontal_ condition was created by retaining only the measurement points on the horizontal plane from the generic HRTF set. Lastly, condition _No HRTF_ was created by disabling the binaural rendering and playing back a mono-downmix of the scene audio that did not react to listener movements.  
There were four scenes focusing on different aspects of localization accuracy (_In scene, Handheld, Above_, and _Below_), two scenes focusing on timbre (_Cello_ and _Castanets_), and two scenes focusing on overall audio quality (_Park_ and _Fountain_). The scenes, task in the scene, and audio content are summarized in Table 2. Visually, all of the scenes presented the participants with a large empty space where a white sphere (\(r=10\) cm) denoted the location of the audio object. The environment was purposefully minimalistic in appearance to provide only the necessary cues to support audio-visual sensory integration, and not distract the participants with too much visual information.  
The audio object was either placed in the scene (_In scene_) at 1.5 m height from the floor level or attached to the hand-held controller (_Handheld_), allowing the participant to move it around their head freely. In the scene _Above_, the audio object was placed 3 m above the floor level, as opposed to being on the floor in the scene _Below_. In these four scenes the audio content was pink noise. In the two scenes focusing on timbre, the audio object was placed at 1.5 m height, and the participant was instructed to stand on a marker 1 m in front of the audio object. These scenes featured anechoic recordings of a cello or castanets.  
The overall quality scenes were composed of two spheres denoting two audio objects placed 3 m from each other at 1.5 m height. In _Park_, the two audio objects were a field recording of ducks and another field recording of shrub pruning with scissor clipping sounds and the rustling of leaves. In the _Fountain_ scene, the audio objects were a dry studio recording of piano performance and a field recording of a water fountain.  
In all of the scenes, the participant's movement was tracked in 6-DoF, and the audio rendering was updated dynamically to reflect the audio object's position in relation to the listener. The update was performed by choosing the nearest HRTF pair without interpolation. The source signals were convolved with each of the HRTF sets under study in parallel in real-time. To enable accurate comparison of the HRTFs, the acoustics of the virtual space were not modeled. The omitted early reflections and reverberation removeany supporting localization cues apart from the directional information in the actual HRTFs under test. Due to the lack of virtual acoustics, the direct-to-reverberant ratio cue was not modeled. Thus, distance rendering relied only on the intensity cue realized by applying the inverse square law with a maximum level reached at 0.1 m from the sound object. Auditory near-field effects were not modeled. Similar to the static localization experiment, the audio was played back through an RME Fireface UCX audio interface and Beyerdynamic DT7/70 Pro headphones.