3.1. Realism of VR Simulations
In the visual only and aural–visual combined condition, participants evaluated their realism on a 7-point rating scale. Results showed a highly perceived realism for most participants. Figure 4
shows means and standard deviation of rated realism for all scenarios under the visual only and aural-visual conditions. Perceived realism was mostly (60% of the participants) rated as moderately realistic and realistic under the visual only condition, with rating scores above 5 (close to very realistic). More than half of the participants (59%) rated aural–visual scenarios with scores above 5. The worst realistic scenarios corresponded to site 4 and site 5 with human voices due to “incongruence of human sound and visual content”, according to their comments. Scenarios at site 1 and site 3 with road traffic sound rating scores above 5 were rated as the most realistic. Therefore, with the aid of VR, the aural–visual interactive and dynamic simulations can create scenarios with a high level of realism. The interactivity and dynamics of the virtual environment could support the public’s understanding of wind park projects.
To improve the simulations, participants rated the seven simulations in the aspects of light realism, color realism, and vegetation realism. Results for each site are listed in Table 2
. A significant correlation was found between total realism, light realism, color realism, and vegetation realism (p
< 0.001). The more realistic the light realism, color realism, and vegetation realism were, the more realism there was in total. The analysis of variance (ANOVA) tests on perceived realism were calculated for different realism metrics (light realism, color realism and vegetation realism) at seven sites. Results confirmed a significant main effect on the realism metrics (F
(3, 39) = 5.079, p
3.2. Aural–Visual Interactions in VR Simulations
In the visual only and aural–visual combined conditions, participants evaluated their acceptance on a 7-point Likert scale. The mean values of the acceptance evaluated for each site for 40 participants are presented in Figure 5
. The evaluation of acceptance of wind parks were conducted in two conditions (visual only and aural–visual conditions), since the aural stimulus was not synthetic but came directly from original binaural recordings. This study intended to avoid confusion and fatigue on the part of the participants in rating these parameters. The data were calculated by a two-way ANOVA test in these two conditions, and seven sites were independent of each other. Acceptance was the dependent variable.
Results showed a statistically significant main effect located at the site (F (6, 39) = 11.75, p < 0.001). No significant main effect was found between two conditions. It could be seen that all of the investigated sites were rated as highly accepted areas for wind parks. This included site 1, with rated acceptance by a score of 5.15; site 2, site 3, site 6, site 7 were 5.38, 5.23, 5.2, and 4.58, respectively. Of all the sites, site 4 and site 5, where human activities took place nearby, had scores of approximately 4, and were rated the least accepted sites.
The results indicated that participants had a relatively high acceptance for wind parks at rural sites, but the addition of human activities could decrease the acceptance for wind parks. People might find wind parks to be clean and meaningful constructions when they were “not in my backyard”. Otherwise, wind turbines might be considered to be ugly and annoying constructions, which converted the natural recreational areas to industrial sites. This study could suggest that planning of wind parks must be restricted near sites of human activities.
Furthermore, participants rated the general annoyance of the simulation under aural only, visual only and aural–visual combined conditions. The ANOVA annoyance test scores were calculated for three conditions (aural only, visual only, and aural–visual conditions) at seven sites. Results showed a statistically significant main effect was in the condition (F
(2, 39) = 20.00, p
< 0.001) and sites (F
(6, 39) = 77.49, p
< 0.001), and also a significant interaction effect was in the condition versus sites (F
(12, 43) = 22.10, p
< 0.001). Mean general annoyance scores in three conditions were plotted in Figure 6
. It was found that annoyance at most sites (site 1, site 2, site 6, and site 7) in the aural–visual condition was closer to the results of the aural only condition than the visual only condition. This result illustrated the fact that the addition of the visual information did not significantly change the perceived annoyance, which may be because of the similarity of the rural environment. In addition, the presentation of visual simulations was not as complex as that of the real site, because detailed visual modeling by hand is time consuming. In this study case, aural information was more influential than visual information with regards to the wind park landscapes.
As could be seen, the addition of aural information decreased the annoyance with the simulation for most sites, except site 2 with dominant natural sounds (birds). Conversely, a significant decrease was shown at site 1 with dominant mechanical sounds (traffic). Finally, site 2 with dominant bird sounds was the most preferred site, and site 1 with dominant traffic noise was the least preferred one. Results indicated that the aural information played an important role for the annoyance of the wind park simulation. Further the addition of human sounds, traffic sounds, or water sounds in the rural region had a negative influence on the preferences of wind parks, while the addition of bird sounds brought a positive effect to the preferences.
The relationship between realism and annoyance was analyzed; however, there was no significant effect. The reason was that, in the specific wind park projects, when the realism of landscape was relatively strong, the primary interactive factor for the annoyance of wind parks could be another important factor, such as the sound pressure level [21
]. Overall, the addition of sound increased the realism of the simulations; however, incongruence of the aural and the visual information could have a strong negative impact on it.
3.3. Soundscape in Multidimensional Scales in VR Simulations
In the VR method in the soundscape study, perceived realism was further explored with soundscape factors. Therefore, a method of the multidimensional scales was used to assess the soundscape at linguistic and psychophysical levels, and determined how the different semantical scales were linked to one another. According to the semantical descriptors, participants rated the seven scenarios. The mean ratings of the bipolar adjectives of the semantical description are shown in Figure 7
. Site 3, site 4, site 5, site 6, and site 7 remain in the middle of the radar circle, except the metric of open/close. However, site 1 located in the outer circle and site 2 located close to inner circle of the radar plot are clearly seen. At the same time, as described above, site 1 with dominant traffic sounds and site 2 with dominant natural bird sounds were rated as the least preferred sites and most preferred sites, respectively. These results are somewhat consistent. They confirm the importance of the semantical characteristics of an ambient soundscape on perception of wind park landscapes. The relationship between the semantical metrics and perceived annoyance will be discussed in the coming paragraph. Furthermore, site 1 was found to be quiet, distinct, natural, open, calming, smooth, and comfortable for the participants, while site 2 was found to be the opposite of site 1. This could be explained by the fact that people prefer landscapes with bird sounds to those with traffic sounds.
The principal component analysis (PCA), a statistical method was proposed to explore communalities in collected soundscape semantical data, and Kaiser–Meyer–Olkin (KMO) was applied within PCA to verify the adequacy of the data and the factor loadings [18
]. The PCA with varimax rotation was thus chosen to extract the orthogonal factors (Table 3
). Three factors were determined to explain their variance. Component 1 was extracted to explain 42% of the variance, which had high positive loadings for “smooth/rough,” “distinct/ordinary,” “quiet/loud,” “order/disorder,” “comfortable/uncomfortable,” and “calming/agitating.” This component could represent “calmness/relaxation” as demonstrated by former researchers [20
]. Component 2 was extracted to explain 16% of the variance, which had high positive loadings for “open–closed,” “natural–artificial” and “pleasant–unpleasant.” Thus, it could be relevant to “naturality/pleasantness.” Component 3 was extracted to explain 11% of the variance, and it had high positive loadings for “various/monotonous,” which could be related to “diversity.” These three components retained orthogonality, which also explains 69% of the variability in the original ten dimensions.
After factor analysis, the strongest factors for explaining the impact on the annoyance with wind park landscapes were achieved. In addition, further analysis of Pearson’s correlation among these factors, perceived realism, annoyance, and psychoacoustic factors were conducted and listed in Table 4
. Mean perceived realism in the aural–visual condition and four psychoacoustic metrics including loudness, sharpness, fluctuation strength, and roughness, were obtained through Artemis (Head Acoustics) Software, and were applied for the correlation analysis. Results showed that “diversity” was related to the perceived realism. “Diversity” of soundscape had a stronger impact on the perceived realism than the others. In order to enhance the reality of the landscape, varieties of soundscapes should be considered. Results also indicated that the factors “calmness/relaxation” and “naturality/pleasantness” were correlated to psychoacoustic metrics “loudness” and “fluctuation strength.” Annoyance with wind parks was significantly correlated to “calmness/relaxation” and “naturality/pleasantness” of the soundscape, marking the importance of “calmness/relaxation” and “naturality/pleasantness” in the evaluation of wind park landscapes.