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

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For example, too small a time difference ∆t will result for a loudspeaker arrangement that
is symmetrical with respect to the frontal plane (Figure 20, δ = 90°). The two maxima at
each ear will appear at the same time; the localisation stimuli are not discriminable.
Consequently, there will be no suppression of sound colouration, which was confirmed
experimentally in Section 2.2.2 (Item 5, Figure 9b, Test signal A4). Furthermore, from
Figure 9b it can be seen that the perceptibility of sound colouration increases as δ 90°.
This is in line with the decrease in ∆t that is evident from Figure 20.
In THEILE / PLENGE 1977 phantom source direction was investigated as a function
of δ. The results showed that:
1. For δ = 90°, the auditory event is located either at the frontal or the rear
loudspeaker, depending on the level ratio of the loudspeaker signals. In principle,
lateral phantom sources do not arise. This is explained by the localisation model if
one assumes that for equal signal levels the localisation stimuli cannot be
discriminated due to identical interaural time differences, but that for unequal
levels one or the other spectrum will dominate.
2. The focus of the phantom source greatly decreases for δ > 60°. The time
differences between the superimposed signals are of the magnitude ∆t < 200 µs
(see Figure 20). It seems that this is where the discrimination threshold of the
localisation stimuli lies.
3. As δ 90°, the direction of the phantom source does not remain in the centre of
the loudspeaker base, but shifts by maximally 10° in the direction of ϕ = 0°. This
effect is in agreement with the fact that for a laterally displaced loudspeaker base
the localisation stimuli will not be simultaneously available. Of course, a
localisation stimulus can only be discriminated if it is available in binaural form.
This will happen later for the signal radiated by the loudspeaker closer to the
frontal plane (Signal B in Figure 20). Thus, the model explains the displacement
from the centre of the loudspeaker base by means of a time difference between the
localisation stimuli. This time difference will have a maximum value of about 200
µs, which, according to measurements made by WENDT 1963, corresponds to a
change of ϕ = 10° … 15° in phantom source direction (see Section 4.3.1).
4.2.4 Auditory events in the case of narrow-band signals
The association model is based on a pattern recognition process that is made possible
by associative stimulus processing. The localisation process thus requires a sound
source that allows for a sufficiently robust distance perception (see Section 3.2.1).
This is the case if spectral characteristics of a current stimulus can be analysed.
Associative stimulus processing necessitates a sufficiently broadband stimulus.