## 3 Results and Discussion  
ANOVA for the SV of the preference revealed that the main effect (i.e., difference between the stimuli) was statistically significant (\(F\) (17, 4184) = 295.7, \(p<0.001\), for birdsong, \(F\) (15, 3479) = 395.1, \(p<0.001\), for insect song). Figure 5 shows the SV of preferences to birdsong and insect song. The most preferred birdsong was _Horornis diphone_. _Horornis diphone_ is one of the three major species of Passeriform in Japan and is considered to produce a beautiful twittering sound. The most preferred insect song was _Teleogryllus emma_. _Teleogryllus emma_ is the largest Grylloidea in Japan, known colloquially as a cricket, and its song is often heard throughout Japan in autumn. It is well known that lexical information on words and contextual information on sentences improve speech intelligibility and play an important role in verbal communication [22]. That is, word familiarity plays an important role in intelligibility. Similarly, familiarity with birdsongs and insect songs may affect preferences. Judgments differed among participants regarding preferences for _Streptopelia orientalis_. All participants judged that _Garrulus glandarius_ was the least preferred birdsong, producing a sound resembling a creaky voice. Two birdsongs, _Zosterops japonicus_ and _Parus minor_, and two insect songs, _Teleogryllus emma_ and _Tanna japonensis_, have similar time patterns and scale values of preference, suggesting that time patterns affect preference. Table 3 shows the correlation coefficients between each physical parameter and subjective preference for birdsongs and insect songs. Figures 6 and 7 show the relationship between representative physical parameter and subjective preference for birdsongs and insect songs. SVs of preference for birdsong and insect song stimuli had a high positive correlation with \(\varphi_{1}\) (r = 0.51, \(p<0.01\); r = 0.54, \(p<0.01\)), and a high negative correlation with \(\tau_{1}\) (r = \(-0.41\), \(p<0.01\); r = \(-0.37\), \(p<0.01\)) and loudness (r = \(-0.54\), \(p<0.01\); r = \(-0.44\), \(p<0.01\)). The correlation coefficients between subjective preference and duration of the birdsong and insect song stimuli were \(-0.17\) and \(0.17\), respectively. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Birdsongs** & **Insect Songs** \\ \hline \(\tau_{1}\) & \(-0.41\)** ** & \(-0.37\)** \\ \(\varphi_{1}\) & \(0.51\)** ** & \(0.54\)** ** \\ \(W_{\varphi(0)}\) & \(-0.13\)** ** & \(0.25\)** ** \\ \(\tau_{\text{e}}\) & \(-0.28\)** ** & \(0.02\) \\ loudness & \(-0.54\)** ** & \(-0.44\)** ** \\ sharpness & \(0.21\)** ** & \(-0.48\)** ** \\ roughness & \(0.04\) & \(0.14\)** \\ ZCR & \(0.13\)** ** & \(-0.64\)** ** \\ entropy & \(0.05\) & \(-0.49\)** ** \\ spectral centroid & \(0.20\)** ** & \(-0.54\)** ** \\ spectral spread & \(0.02\) & \(0.37\)** ** \\ spectral entropy & \(-0.04\) & \(-0.59\)** ** \\ spectral rolloff & \(0.02\) & \(0.47\)** ** \\ spectral flux & \(0.14\)** & \(-0.68\)** \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Correlation coefficients between each physical parameter and subjective preference for birdsongs and insect songs. Asterisks indicate the level of significance, i.e., **_p_ \(<0.01\), *_p_ \(<0.05\). Figure 5: Scale values of preferences for **(a)** birdsong and **(b)** insect song. Each symbol indicates the mean value and error bars indicate standard deviations. Sounds with higher \(\varphi_{1}\) have a salient pitch [15] and noises with lower \(\varphi_{1}\), such as those generated by a refrigerator [23] or an air conditioner [24], tend to cause more annoyance. These findings suggest that birdsong and insect song stimuli with a salient pitch, which have \(\varphi_{1}\) values around 0.9, are preferable. It has been reported that the tonal component, which is correlated with \(\varphi_{1}\) value, causes annoyance [25]. Although this is not consistent with the present findings, it can be explained by periodic variations in the amplitude and frequency of birdsongs and insect songs.