## 2 Literature Review  
### Presence and Auditory Characteristics of a Metaverse Environment  
An aspect that should be considered to provide a more realistic experience in the field of the metaverse is the sense of presence, which is considered an essential prerequisite for visual, tactile, and auditory factors [12]. The sense of presence considered in metaverse environments is related to sensations such as perceiving oneself as existing in a virtual space [20] or being transported to a virtual space [21], and the feeling of 'being there', i.e., the subjective experience of the receiver focusing on and immersing themselves in the virtual world [22]. In metaverse environments, presence is also related to the perception of the user and others with whom they interact, including the experience of perceiving virtual objects as if they were real [23], the degree to which the user identifies with the avatar's body [24], the degree to which they feel they are interacting with others [25; 26], and the degree to which the recipient attributes personality to virtual humans, making them perceive them as social actors [27; 28]. Therefore, the sense of presence can be categorized as the feeling of being transferred and immersed in a virtual world [20; 21; 22], the feeling of similarity to a real person [23; 25], and the feeling of similarity in social behavior [25; 26; 27; 28]. Table 1 shows the definitions and classification of presence by researchers. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Researchers** & **Definition of Presence** & **Classification of Presence** \\ \hline [PERSON] et al. (1997) [20] & Subjective sensations, such as being transported to a & \\ [PERSON] (1992) [21] & virtual space & A sense of transference and immersion \\ \hline [PERSON] et al. (1998) [22] & The cognitive process of focus and engagement and the & in the virtual world \\  & subjective experience of the receiver & \\ \hline [PERSON] et al. (1998) [23] & How much the avatar’s body identifies with the user & \\ \hline [PERSON] et al. (1997) [24] & The experience of feeling that a person exists in a & Similarity to real people \\  & virtual environment & \\ \hline [PERSON] et al. (2001) [25] & How much you feel connected to others & \\ \hline [PERSON] et al. (1976) [26] & & Similarity to social behavior \\ \hline [PERSON] et al. (1982) [27] & Recognizing virtual humans as social actors & \\ \hline [PERSON] et al. (1997) [28] & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Definition and classification of presence by researchers. In a metaverse environment, presence is interrelated with spatial, temporal, and acoustic properties related to hearing. Spatial characteristics refer to where the sound is coming from, temporal characteristics refer to when the sound is heard, and acoustic characteristics refer to the pitch or intensity of the sound. These characteristics are based on the concept of the binaural effect, in which the brain analyzes factors such as the time difference between the sound source and the sound pressure difference between the two ears to determine where the sound is coming from within the sound field. This means that there are differences in the spatial perception of sound due to the diffraction, reflection, and absorption of sound from the sound source to the ear and body characteristics. Based on this, there are three main criteria for determining the location of a sound source in three-dimensional space: the time difference between the two ears (ITD, interaural time difference), the level difference between the two ears (IID, interaural level difference), and the frequency characteristics (spectral cue) [29; 30; 31]. The auditory evaluation factors of a metaverse environment can be derived by identifying the auditory factors that make the metaverse environment feel real [21].