# Creating Audio Object-Focused Acoustic Environments for Room-Scale Virtual Reality
## 5 Evaluation/Results
### Collision-Based System  
To demonstrate the spatial benefits and audio-visual synchronization, the authors compare the application of the collision-based system with an alternative approach based on the playback of a static Ambsonic recording. Both are built from one element (\"water droplets\") of one of the prototype's acoustic environments. The authors manually approximated the neural features of the Ambsonic version with the original object-based version in a DAW. Both audio representations share the same visual scene; the water droplet's visual representation in time and space is generated randomly in both cases.  
The object-based version is created using the following steps. A dry, in situ recording of water droplets is segmented into several small sound files; the resulting files are grouped into four levels representing different impact forces; impact forces are assigned to a parameter exposed to Unity and mapped to the impact collision velocity of the water droplet's visual representation; the visual representation of the droplet's collision with the floor or the player triggers the water droplet's sound; the position of the collision is matched to the spatialized sound's position; the player's distance to the spatialized sound's position affects its direct signal level and a high-pass filter's cutoff frequency removes the sound's low-frequency content. As a result, the water droplet will sound brighter, quieter, and more reverberated as its proximity to the player decreases.  
The Ambsonic recording method approximates the object-based version via the following steps. First, the same source recording is divided into small segments; each segment is assigned to one of five positions around the virtual listener in the DAW at different distances; each position is spatialized using first-order Ambsonic encoding via dearVR pro [63]; the resulting Ambsonic recording is reverberated using an impulse response generated from within the environment's real-time room simulation; the recording is looped, placed in the center of the environment, and starts playing at the beginning of the scene.  
Video S5 (05_rainAmbiObj.mp4) shows the spatial, interactive benefits of the audio object-focused approach. This screencast presents a fly-through through the environment of the Ambsonic version first, followed by a fly-through of the object-focused version (visible at timecode 0:37). In the object-focused version, the collision sound of each water droplet matches its visual representation in space. Their distinct aural localization facilitates transitions across acoustic environments: when the player stands on the threshold of one environment, all the droplets sound distant, whereas in the middle of this environment, some droplets sound close, while others sound distant. Furthermore, integrating sound file playback in the collision system aligns the visuals with the audio in time and space (see also Video S2: 02_collision.mp4). The transient nature of the water droplets limits active player participation in both cases. However, the object-focused approach provides interactivity to the sound designer, making the acoustic environment malleable in real time. For instance, the density of the water droplets can be easily adjusted in real time by changing the generator's instantiation frequency.  
In contrast, while the Ambsonic version also creates a sense of space, it does not respond to the player's position dynamically. This means that some water droplets sound always close, while others sound always distant. Furthermore, the sounds cannot be aligned in time and space to the water droplet's visual representation due to the randomness of their generation (unless their pattern of appearance would be predetermined). A change in the density of water droplet generation would require the sound designer to re-design, re-render, and reimport the Ambsonic recording.