Vertical Stereophonic Localisation in the Presence of Interchannel Crosstalk: the Analysis of Frequency- Dependent Localisation Thresholds

Listening tests were conducted in order to investigate the frequency dependency of localization
thresholds in relation to vertical interchannel crosstalk. Octave band and broadband pink
noise stimuli were presented to subjects as phantom images from vertically arranged stereophonic
loudspeakers located directly in front of the listening position. With respect to the
listening position the lower loudspeaker was not elevated; the upper loudspeaker was elevated
by 30◦. Subjects completed a method of adjustment task in which they were required to reduce
the amplitude of the upper loudspeaker until the resultant phantom image matched the position
of the same stimulus presented from the lower loudspeaker alone. The upper loudspeaker was
delayedwith respect to the lower by 0, 0.5, 1, 5, and 10 ms. The experimental data demonstrated
that the main effect of frequency on the localization threshold was significant, with the low
frequency stimuli (125 and 250 Hz) requiring significantly less level reduction (less than 6 dB)
than the mid-high (1, 2, and 8 kHz) frequency stimuli (9–10.5 dB reduction). The main effect
of interchannel time difference (ICTD) on the localization thresholds for each octave band was
found to be non-significant. For all stimuli interchannel level difference (ICLD) was always
necessary, indicating that the precedence effect is not a feature of median plane localization.