Improving the sound quality of guiding chimes for the visually impaired to reduce annoyance to the sighted

In Japan, guiding chimes are installed in public areas to assist the mobility of the visually impaired. The guiding chimes consist of periodically sounding two-pitch combinations, and are seen as an effective tool for the visually impaired. However, annoyance is often caused to sighted people working near the chimes. A questionnaire survey of workers around a railroad station that has guiding chimes installed showed that the 47/75 respondents reported annoyance caused by the chimes. They also referred to the guiding chimes' unpleasant sound quality. Rating experiments were conducted to determine the acoustic features of chimes with the aim being to reduce auditory unpleasantness. Temporal and spectral conditions that could help reduce auditory unpleasantness were obtained. A suitable duration for each tone was 1.0 to 1.5 s, a suitable attach time for each tone was 3 to 10 ms, and a suitable decay rate was around 25 dB/s. Chimes were found to be more pleasant when they consisted of only odd harmonics than when made up of all harmonics. The unpleasantness increased according to the enhancing intensity of higher harmonics when chimes consisted of all harmonics. However, when chimes consisted of odd harmonics, they maintained the same pleasantness level even when the intensity of the higher harmonics increased. The effect of the spectral features of chimes on auditory pleasantness was greater than that of the temporal features. The audibility of the proposed type of pleasant chime was not degraded in environment noise when comparing with the normally used guiding chimes. The accuracy of localization of the proposed chimes was equivalent to that of conventional guiding chimes.