A study on the precedence effect in various background sounds
Takahiro Fujikawa, Shigeaki Aoki · 2010
In this paper, we investigated the precedence effect in combination of four signals and three background sounds with three level differences between the signal and background sound. In subjective tests, four signals were male voice, female voice, siren tone and sweep tone. Three background sounds were recorded in a mall, a hotel and a corridor of school. The durations of signals were 3-8 seconds. The background sound started two seconds before the head of the signal and stopped two seconds after the tail of the signal. The level differences between the signal and background sound were -6, 0 and +6 dB. The test signals were created on the assumption that a direct sound and the first reflective sound surrounded by non-directional background sound. The direct signal and the first reflective signal came from loudspeakers that were set at the 45 degrees point left and right from the median plane of a listener, respectively. Not only direct signal from the loudspeaker to the listener but also crosstalk-signal from the opposite loudspeaker to the listener were calculated using HRTFs (Head related transfer function). The distance between the loudspeakers and the listener was 1.4 m due to measurement condition of the HRTF. The delay time of the first reflective signal were changed from 0 to 80 ms in twelve steps. Non-directional background sound was designed that background sound was radiated from 36 loudspeakers arranged at equal intervals on the circumference of 1.4 m in radius and was calculated using the HRTFs. One listening session consisted of five trials in each delay time. The kinds of delay times were twelve. The listeners randomly listened to a test signal 60 times in each session. There were three sessions for each condition. Two males in age of twenties took part in the tests. The subjective test showed that the level difference between the signal and background sound and the combination of signal and background sound contributed to the direction of sound localization when the precedence effect occurred. Moreover, the combination of signal and background sound influenced the stability of sound localization. The female and male voices showed the almost same tendency, however, non-voice signals, that is, siren tone and sweep tone showed the different tendency from the voices. It was confirmed that when the precedence effect occurred in background sound, the complicated structure of signal had an effect on the degree of the occurrence.