In order to realize binaural auralizations with head tracking, BRIRs of individual listeners are needed for different head orientations. In this contribution, a filter-and-sum beamformer, referred to as virtual artificial head (VAH), was used to synthesize the BRIRs. To this end, room impulse responses were first measured with a VAH, using a planar microphone array with 24 microphones, for one fixed orientation, in an anechoic and a reverberant room. Then, individual spectral weights for 185 orientations of the listener’s head were calculated with different parameter sets. Parameters included the number and the direction of the sources considered in the calculation of spectral weights as well as the required minimum mean white noise gain (WNGm). For both acoustical environments, the quality of the resulting synthesized BRIRs was assessed perceptually in head-tracked auralizations, in direct comparison to real loudspeaker playback in the room. Results showed that both rooms could be auralized with the VAH for speech signals in a perceptually convincing manner, by employing spectral weights calculated with 72 source directions from the horizontal plane. In addition, low resulting WNGm values should be avoided. Furthermore, in the dynamic binaural auralization with speech signals in this study, individual BRIRs seemed to offer no advantage over non-individual BRIRs, confirming previous results that were obtained with simulated BRIRs.

In order to make full use of their potential to replace experiments in real rooms, auralizations must be as realistic as possible. Recently, it has been shown that for speech, head-tracked binaural auralizations based on measured binaural room impulse responses (BRIRs) can be so realistic, that they become indistinguishable (or nearly so) from the real room [1, 2]. In the present contribution, perceptual comparisons between the auralized and the real room are reported for auralizations based both on measured and simulated BRIRs. In the experiment, subjects sitting in the real room rated the agreement between the real and the auralized room with respect to a number of attributes. The results indicate that for most attributes, the agreement between the auralized and the real room can be very convincing (better than 7.5 on a nine-point scale). This was not only observed for auralizations based on measured BRIRs, but also for those based on simulated BRIRs. In the scenario considered here, the use of individual head-related impulse responses (HRIRs) does not seem to offer any benefit over using HRIRs from a head-and-torso-simulator.

As an alternative to conventional artificial heads, a virtual artificial head (VAH), i.e., a microphone array-based filter-and-sum beamformer, can be used to create binaural renderings of spatial sound fields. In contrast to conventional artificial heads, a VAH enables one to individualize the binaural renderings and to incorporate head tracking. This can be achieved by applying complex-valued spectral weights—calculated using individual head related transfer functions (HRTFs) for each listener and for different head orientations—to the microphone signals of the VAH. In this study, these spectral weights were applied to measured room impulse responses in an anechoic room to synthesize individual binaural room impulse responses (BRIRs). In the first part of the paper, the results of localizing virtual sources generated with individually synthesized BRIRs and measured BRIRs using a conventional artificial head, for different head orientations, were assessed in comparison with real sources. Convincing localization performances could be achieved for virtual sources generated with both individually synthesized and measured non-individual BRIRs with respect to azimuth and externalization. In the second part of the paper, the results of localizing virtual sources were compared in two listening tests, with and without head tracking. The positive effect of head tracking on the virtual source localization performance confirmed a major advantage of the VAH over conventional artificial heads.

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In binaural synthesis, the playback device (typically: headphones) can play an important role in achieving the desired perceptual authenticity. One potential source of error is the variability of headphone transfer functions when the headphones need to be taken off and on again after equalization. To avoid this issue, Erbes et al. (2012) proposed a device with miniature loudspeakers located about 5 cm away from the ears, which could remain in place. However, the device itself forms an obstacle not present in normal listening conditions and may therefore introduce direction-dependent artifacts. As an alternative, we propose a device which is placed in the subjects' ear canals. Due to its small size and the position in the ear canal, it is hoped that artifacts will be independent of the direction of sound incidence. In order to compare the two devices which remain in place to the more traditional playback over classical headphones, binaural syntheses were generated for 432 source positions (12 elevations and 36 azimuths) and related to transfer functions from real sources to microphones of a dummy head with ear canals. It was found that the agreement between synthesis and measurement was best with the in-ear device.