Subjective Salience of Birdsong and Insect Song with Equal Sound Pressure Level and Loudness

Birdsong is used to communicate the position of stairwells to visually impaired people in train stations in Japan. However, more than 40% of visually impaired people reported that such sounds were difficult to identify. Train companies seek to present the sounds at a sound pressure level that is loud enough to be detected, but not so loud as to be annoying. Therefore, salient birdsongs with relatively low sound pressure levels are required. In the current study, we examined the salience of different types of birdsong and insect song, and determined the dominant physical parameters related to salience. We considered insect songs because both birdsongs and insect songs have been found to have positive effects on soundscapes. We evaluated subjective saliences of birdsongs and insect songs using paired comparison methods, and examined the relationships between subjective salience and physical parameters. In total, 62 participants evaluated 18 types of bird songs and 16 types of insect sounds. The results indicated that the following features significantly influenced subjective salience: the maximum peak amplitude of the autocorrelation function, which signifies pitch strength; the interaural cross-correlation coefficient, which signifies apparent source width; the amplitude fluctuation component; and spectral content, such as flux and skewness.