## 3 Part I: Localization of Real and Virtual Sources in the Absence of Visual Cues
### Experiment Design
#### 3.1.3 Localization of Virtual Sources (TestVR)  
To generate the binaural signals for TestVR, both VAHs were positioned at the listener position in the anechoic room. The same loudspeaker arc in combination with the turntable as described in Section 3.1.2 was used to measure the room impulse responses among the microphones of VAH1 and VAH2 and each of the target source positions shown in Figure 2b. In order to keep the acoustic conditions comparable to TestReal, the VAHs were placed inside the acoustically transparent tent during the measurements of room impulse responses (see Figure 3c). These room impulse responses were used together with spectral weights calculated individually for 37 \(\times\) 5 = 185 head orientations with VAH1 and VAH2, using the parameters listed in Table 1, to synthesize individual binaural room impulse responses (BRIRs) as follows: the \(N\) individually calculated left and right spectral weights for a given head orientation were transformed to left and right FIR filter coefficients using the inverse Fourier transform. The measured room impulse response between a given  
Figure 2: Target positions when localizing with **(a)** real sources in TestReal, **(b)** virtual sources in TestVR and **(c)** virtual sources in TestDynamic and TestStatic. Numbers outside and inside the circle indicate the azimuth angles and the levels of elevation of the target sources, respectively. target source and each of the \(N\) microphones was convolved with the associated FIR filter. The sum of the filtered room impulse responses over the \(N\) channels resulted in left and right BRIRs for the given target source and the given head orientation. This resulted in four sets of individually synthesized VAH BRIRs, synthesized with V11, V13, V21 and V23, each for 185 head orientations. In addition, for each of the target source positions shown in Figure 2b, BRIRs were acquired with the two ears of a KEMAR artificial head (GRAS KEMAR type 45 BB) placed at the listener position inside the acoustically transparent tent. In order to enable a dynamic presentation and similarly to the previous studies in [12,13], for each of the target source positions shown in Figure 2b, the BRIR measurement was repeated for 37 horizontal head-above-torso orientations of the KEMAR artificial head (\(-90^{\circ}\) to \(+90^{\circ}\) in \(5^{\circ}\) steps), resulting in \(37\times 15=555\) measurements. It should be mentioned again that for signals recorded with conventional artificial heads, dynamic presentation of the recordings is not possible in practice. The additional effort to measure BRIRs for different head-above-torso orientations of the KEMAR artificial head was only accepted in the present study because otherwise, signals generated with KEMAR BRIRs would clearly lose out against signals generated with the VAH BRIRs during the localization experiments. The BRIRs measured for 37 head-above-torso orientations of the KEMAR artificial head were referred to as HTK (head-tracked KEMAR). During TestVR, each subject sat with his interaural center at the listener position inside the acoustically transparent tent and the room was darkened. Subjects wore head-phones (Sennheiser HD800--the same as used to measure the individual HPIRs) with a custom-made head tracker mounted on top. The real-time head-tracked binaural playback was generated with a custom C++ program based on [18]. BRIRs corresponding to the current head orientation were filtered with the inverse individual HPIRs prior to being convolved with the test signal within the real-time dynamic playback program. Audio signals were presented over an RME Fireface UC sound card and a Lake People Phone-Amp G103 headphone amplifier. Subjects were instructed to reset the head tracker before listening to the virtual source by keeping their heads oriented forward, indicated with a mark on the top of the tablet monitor in front of them, and pressing the \"Reset\" button on the GUI.