on the localisation in the superimposed soundfield - Hauptmikrofon ...

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distance perception is not influenced by the comb filter effect, and neither do the
linear distortions (see Section 2.2.1) cause inside-the-head locatedness, nor do they
prevent front-back reversals (THEILE 1975).
The elevation effect can be attributed to the localisation stimulus selection, too. If two
loudspeakers (arranged symmetrically with respect to the median plane) are moved on
a circle in the horizontal plane with the listener being positioned in the centre, the
auditory event location in the median plane will move with the discriminated average
source distance. The mean of the distance and direction lies on a circle in the median
plane. The elevation angle results from sound colour properties that, due to the
localisation stimulus selection, are not influenced by the comb filter effect.
This is proven by the fact outlined in Section 2.2 that equivalent interchannel level and time
differences (loudspeakers positioned at the listener’s sides along the interaural axis) do not
lead to different elevations of the phantom source, even though spectral differences will
occur in the crucial frequency region around 8 kHz (see BLOOM 1977). If the listener
moves the head sidewards by a few centimetres in the direction of one loudspeaker, the
resultant change of the (elevation-salient) spectrum will be very different from the change
that a head rotation in front of a substitute (real) sound source would produce.
The spectrum salient to perceived elevation is not the resulting spectrum of the ear
signals, but the average spectrum of the two ear signals that the loudspeakers produce
separately. If, as a result of the localisation stimulus selection, the distance e and
horizontal direction ϕ of the phantom source have been determined, it will be located
on a circle with the radius e. The plane of this circle will be perpendicular to the
horizontal plane and will exhibit the direction ϕ.
The position on the circle is determined by the average spectrum, i.e. the phantom
source will be perceived to be at the location at which its sound colour characteristics
match those of a substitute sound source as closely as possible.
This notion explains the measurements made by DAMASKE 1969/70 who
determined perceived elevation as a function of the angle of the stereo base ∆Ω= 2|Ω A |
= 2|Ω B | using band-limited noise (0.65 to 4.5 kHz) as the test signal. In principle, he
found that as ∆Ω 180° the elevation angle ε 90°, even though the directiondetermining
frequency band was not contained in the noise signal. Regrettably,
DAMASKE did not report the associated distances of the auditory events. The result
contradicts the summing localisation principle.
Furthermore, the association model predicts a dependency of the elevation and distance of a
phantom source onto the bandwidth of the signal. If the bandwidth is below a critical value,
localisation stimulus selection is not possible. In this case, elevation and distance perception
do no longer result from the spectra that the loudspeakers produce individually.