The relationship between interchannel time and level differences in vertical sound localisation and masking

Listening experiments were conducted with a pair of vertically arranged loudspeakers. A group of subjects measured the level of delayed height channel signal at which any subjective effects of the signal became completely inaudible (masked threshold) as well as that at which the perceived sound image was localised fully at the lower loudspeaker (localised threshold), at nine different delay times ranging from 0 to 50ms. The sound sources were anechoic recordings of bongo and cello performance excerpts. At the delay times up to 5ms, source type did not have a significant effect for both threshold results and neither threshold varied significantly as the delay time increased. In this time range the average level reduction required for a full image shift was 6∼7dB while that for masking was 9∼10dB. At the higher delay times, on the other hand, both thresholds decreased as the delay time increased and the difference between the two sources in both threshold results was significant. Furthermore, the relationship between the two thresholds varied depending on the source type.