Frequency dependency of localisation threshold in vertical stereophonic and quadraphonic reproductions

This paper describes subjective experiments conducted to investigate the frequency dependency of localisation threshold in vertical stereophonic and quadraphonic reproductions. The localisation threshold here is defined as a minimum level difference of the upper loudspeaker layer (elevated at 30 degrees) to the lower loudspeaker (ear level) layer that is required for the resulting vertical phantom image to be localised at the same height as the image produced by the lower layer. Transient and continuous octave-band and broadband pink noise signals were used as stimuli. The time delays of 0, 1 and 10ms were applied to the upper loudspeaker signal. Results showed that the localisation thresholds varied significantly for different octave bands. The difference between the vertical stereophonic and quadraphonic conditions in localisation threshold was found to be insignificant. The thresholds for the transient stimuli were found to be generally higher than those for the continuous ones, with significant differences found for the 500, 1000 and 2000 Hz bands. Additionally, no evidence was found to support the operation of the precedence effect in both vertical reproduction conditions. It is considered that the results have useful practical implications for designing 3D microphone.