# Creating Audio Object-Focused Acoustic Environments for Room-Scale Virtual Reality
## 1 Introduction  
Room-scale VR using head-mounted displays (HMD) allows the player to move around in the virtual environment, causing new challenges in creating engaging user experiences [1]. This affordance in movement creates a sense of agency in the player that can be addressed through participatory, process-oriented narratives [2]. This affordance for movement and interactivity stems from modern VR systems, such as the Meta Quest 2 [3], being able to track the position and rotation of the player's limbs in six degrees of freedom (6-DoF). However, creating audio that supports these affordances requires new methodologies ([4], Chapter 3). Current recommendations for VR sound design suggest separating an audio mix into foreground and background sounds and applying dedicated spatialization techniques [5]. For example, foreground sounds would be spatialized into a sound-field representation according to their relative position and rotation to a virtual listener (\"object-based rendering\") and accompanied by an additional sound-field recording of an acoustic environment (\"Ambisonic bed\"), such as a recording of a forest or empty office [5, 6]. The resulting sound-field would be transformed into a 3D binaural representation for a listener's left and right ear, based on the listener's head rotation ([7], p. 9). However, such Ambisonic beds can become problematic in large, interactive virtual environments, as the player cannot approach or interact with the sounds of the Ambisonic bed. This is due to the latter being fixed to the player's position [5]. This behavior can break the impression of the player's movement in space, as illustrated in Video S1 via a flythrough of a virtual outdoor environment that uses a single, looped Ambisonic recording (Video S1: 01_problemIllus.mp4). (The link to the supplementary videos can be found in the Supplementary Materials section [8].) This issue can also be observed at the beginning of the VR game _Virtual Virtual Reality 2_[9], in which the position of the visual representation of a flock of birds does not align with its acoustic representation. The potential for contradicting the player's movement in space via positionally unresponsive audio can be further aggravated using invisible, non-diegetic music. Here, the music would be placed outside the game world using stereophonic panning [10]. This placement prevents the player from approaching its source and restricts the music's response to the player's head movement, causing it to appear head-locked [11]. The spatial cues of the music, therefore, may differ from the spatial cues of the game world, which could lead to confusion among the players. Unfortunately, replacing the use of Ambisonic beds or non-diegetic music through an alternative methodology is non-trivial. Recordings capture not only sounds but also their behavior over time, such as the density of occurrence of a particular sound or their change in timbre [12]. Furthermore, the composition of acoustic environments can vary over time, affected, for example, by the time of day [13]. A recording of such an environment may capture such changes, which a composer could choose to use creatively [14]. In this sense, recordings also capture the sonic organization of an environment at one or more moments in time. Consequently, if the use of Ambisonic beds/non-diegetic music were replaced by another methodology, the latter needs to include a method to describe the temporal (and spatial) evolution of its associated sound sources. Furthermore, the type of interactivity to which audio reacts must be considered. Interactivity can be differentiated between active and passive player participation [15]. Passive participation would require the rendering of sounds relative to the user's head orientation and position in space; active participation would require direct manipulable elements to the user [15]. An experience should cater to both types of participation to \"achieve a total experience\" [16].