## 5 Discussion
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multicolumn{6}{c}{**Characteristics of the Acoustic Environment**} & \multicolumn{4}{c}{**Recommended Techniques**} \\ \hline
**Spatial** & **Type of** & **Movements** & **Virtual Sound** & & & & **Use Cases(s) (Selected)** \\
**Spatial** & **Environment**2 [FOOTNOTE:2]Footnote 2: Spatial fidelity refers to the quality of the perceived spatiality (location of sound in 3D space) of sound sources, which directly influences the auditory sensation. 2 Acoustic environments can be real, captured, and reproduced (R), or synthesized from existing sound tracks (S). 3 As described in Section 5. 4 Refers to listeners’ translation movements. The virtual sound reproduction must be able to adapt the sound to translation movements. 5 Refers to binaural rendering with individualized HRTFs. 6 Requires convolution of down-mixed binaural with individualized HRTFs. 7 This refers to the case of recreating a virtual soundscape in a real acoustic environment. * Note that not all spatial audio recording and reproduction techniques reviewed have been used in soundscape studies, e.g., personalized binaural recording and rendering. The perceptual accuracy and ecological validity of these techniques need to be further examined. \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Recommended audio reproduction and recording techniques for virtualizing/augmenting acoustic environments. The acoustic environment characteristics are organized firstly by its type, namely: (1) \"Virtual(R)\", a simulated environment reproduced from recordings at a real location; (2) \"Virtual(S)\", a simulated environment produced by auralization [81]; and (3) \"Real\", the actual physical environment. Next, the characteristics based on interactivity of the listener in the acoustic environment is identified. The interactivity or 'Movement' characteristics in the table are extremely relevant for VR and AR applications, as described in Section 4 For instance, the sound has to be in sync with the receivers' positional and head movements as in the real environment (for AR) or in the virtual environment (in VR). The ability to localize sound sources in the acoustic environment is also an important characteristic, which is also included and labelled as \"Virtual sound source localization\" in Table 3. The degree of localization is further categorized into 0D, 1D, 2D, 3D\(-\), and 3D+. Virtual sound source localization in: (1) 0D refers to the perception with no spatial cues; (2) 1D refers to sound perception limited to left and right in horizontal plane; (3) 2D refers to sound perception with the inclusion of azimuthal and elevation dimensions; and (4) 3D refers to the sound perception with azimuth, elevation and distance, where \(-\) and \(+\) shows poor and good performance, respectively. Lastly, based on the degree of movement and localization characteristics, the spatial fidelity of the acoustic environment is simply classified into three grades for simplicity: Low, Medium, and High. The description of the acoustic environment characteristics in Table 3, are accompanied by their respective reproduction and recording techniques. The limitations of the soundscape study, in terms of the spatial characteristics of the acoustic environment, can be decided by referring to Table 3. For reference, past soundscape evaluation studies are included in the last column of the table. It should be stressed that Table 3 does not suggest that all soundscape studies should employ high spatial fidelity audio, but instead provides a guide to construct the experimental conditions needed for soundscape research.