Auditory impression of amplitude-modulated vehicle horn sounds and their detectability in noisy environment

Vehicle horn sounds, due to their high sound pressure levels, induce negative psychological reactions in listeners, especially pedestrians. In order to reduce such negative effects, a horn sound with a lower sound pressure level is desired. At the same time, a horn sound should be easily perceived by drivers, considering its use on busy roads. The amplitude-modulated horn sound may help to solve these problems. Therefore, we synthesized amplitude-modulated horn sounds, and conducted psychoacoustical experiments to investigate the relationship between the acoustic characteristics and the perceived quality of these sounds. The results showed that stimuli with shallower modulation depths were less unpleasant than those with deeper modulation depths, and stimuli with modulation frequencies below 40 Hz suppressed auditory unpleasantness more than those with higher modulation frequencies. To confirm their effectiveness for detection in noisy conditions, stimuli with different signal-to-noise ratios were created by combining the amplitude-modulated horn sound and road traffic noise. The amplitude-modulated horn sound in road traffic noise was detected even in conditions where the signal-to-noise ratio was 3 dB lower than when the horn sound was not amplitude-modulated. The results indicate that amplitude-modulated horn sounds have the potential to improve the sound environment around roads.