## 2 Literature Review
### Prior Research on Auditory Presence in a Metaverse Environment  
In addition to the implementation of acoustic technologies such as soundscapes that embody real-world sounds [39; 40; 41; 42; 43; 44], studies on the quality of sound sources [39; 44], studies on the stereophonics of sounds [39; 44], studies on the spatial characteristics of sounds [43; 44; 45], studies on auditory cues that help with navigation tasks [44], and studies on auditory factors that match visuals [40; 42] and factors such as coherence between sounds [14] have been identified as influencing the sense of presence. Table 3 shows research examples of the auditory presence evaluation factors in metaverse environments identified by researchers.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Researchers** & **Contents of the Study** & **Auditory Presence** & **Classification** \\  & & **Evaluation Factors** & **of Presence** \\ \hline  & & Implementing real-world & \\  & & sounds & \\ [PERSON] (1993) [39] & Theory and technology on the five senses that enhance the sense of reality in the metaverse environment & Creating a three-dimensional space for sound & Presence \\  & & Sound source quality & \\ \hline  & & Delivering the sound that you expect visually & \\ [PERSON] et al. (2004) [40] & The function and role of soundscapes in a metaverse environment & Auditory experiences that match motion but do not loop & Presence \\ \cline{2-4}  & & Recreating soundscapes & \\ \hline [PERSON] et al. (2010) [41] & How everyday sounds affect the sense of presence in a metaverse home environment & Everyday soundscapes & Social presence \\ \hline  & A conceptual framework for the relationship between sound and immersion, illusions of place, illusions of plausibility, and virtual body ownership in a metaverse environment & Spatial properties of sound Presence with and without auditory backgrounds & Presence \\ \cline{2-4}  & & Consistency between sounds & \\ \cline{2-4}  & & Sound quality & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Auditory presence evaluation factors for metaverse environments identified by researchers.  
As shown in Table 3, the research cases of auditory presence evaluation factors in metaverse environments presented that even the same kind of auditory presence evaluation factors were classified as different presence factors by individual researchers. In the case of'spatial acoustics', some studies classified presence as presence [39; 43; 44], while others classified presence as immersion [42], presence [44], and social presence [45]. Studies on'soundscapes' classify presence as presence [40] and social presence [41], and studies on 'auditory factors related to visual experience' classify presence as presence [40] and presence and immersion [42]. In other words, auditory presence factors have not yet been systematically organized as they were classified differently by different researchers. This result is consistent with a literature review that found it difficult to generalize about auditory presence [12]. Against this background, the study focuses on auditory presence, which is the most basic and essential element of virtual worlds, i.e., the feeling of 'being there', and the auditory sensation such as the transfer of sounds from the physical world to the virtual space, among various concepts of presence.