# Auralization of High-Order Directional Sources from First-Order RIR Measurements
## 3 Listening Experiment--Comparative Study
### Auralization Techniques--Virtualizations of the IKO
All other processing stages are rather specific per auralization technique and are therefore described separately below. _Dummy head BRIR-based (Dy):_ The _Directivity_ and the _Room Transfer Function_ are inherent in the directly measured multiple orientation BRIRs (MOBRIRs) between each loudspeaker of the IKO and the KU100 ([[https://en-de.neumann.com/ku-100](https://en-de.neumann.com/ku-100)]([https://en-de.neumann.com/ku-100](https://en-de.neumann.com/ku-100))) dummy head. Here, we used an orientation resolution of \(\Delta\varphi=15^{\circ}\) on an interval between \(\varphi=[-45^{\circ},\ldots,45^{\circ}]\) to obtain the MOBRIRs and the data is available online ([[https://phaidra.kug.ac.at/o:104386](https://phaidra.kug.ac.at/o:104386)]([https://phaidra.kug.ac.at/o:104386](https://phaidra.kug.ac.at/o:104386))). The _Dy_ technique, the _Dynamic Binural Rendering_ is achieved by the linear interpolation with switched high frequency phase (LISHPh) method as described in [42]. In accordance with the findings in [22], setting the crossover \(f_{c}=2 kHz\), \(\Delta\varphi=15^{\circ}\), and \(L=16\) allows for high-quality BRIR-based binaural rendering, and thus this condition is used as a perceptual target in the study. The processing steps of the reference auralization are shown in the top row of the block diagram in Figure 3. Although the auralization quality (audio quality and spatial mapping) of the _Dy_ technique is expected to be high, the measurement effort for the multiple orientations is somewhat enlarged, and the specific dummy head HRIRs cannot be exchanged unless multi-orientation measurement are repeated with other receivers, dummy heads, or individual subjects, separately. _IKO to em32 MIMO RIR (Em):_ Here, the _Directivity_ and the _Room Transfer Function_ are represented by the measured array domain MIMO RIRs between the 20 IKO loudspeakers and the 32 microphones of the em32 ([[https://mhacoustics.com/products](https://mhacoustics.com/products)]([https://mhacoustics.com/products](https://mhacoustics.com/products))). The resulting em32 signals are transformed in the Ambisonics domain using the state-of-the-art encoder presented in [36,40] and are finally binaurally rendered. An evaluation of this specific auralization technique can be found in [25] and the inherent processing stages are depicted in the second row of Figure 3. The underlying MIMO RIRs are accessible online ([[https://phaidra.kug.ac.at/o:104385](https://phaidra.kug.ac.at/o:104385)]([https://phaidra.kug.ac.at/o:104385](https://phaidra.kug.ac.at/o:104385))). Measuring with the em32 or other higher-order compact spherical microphone arrays increases the hardware effort in terms of channel counts, but permits modular exchange of the receiver directivities or HRIRs, and achieves a native higher-order resolution at the receiver side. Further resolution enhancement by HOSIRR [43] is thinkable but was not used here. _Multi ASDM RIRs (As):_ This approach employs the first-order tetrahedral ST450 microphone array at the receiver side for measuring the \(20\times 4\) (IKO to ST450) MIMO RIRs, which are available online ([[https://phaidra.kug.ac.at/o:104384](https://phaidra.kug.ac.at/o:104384)]([https://phaidra.kug.ac.at/o:104384](https://phaidra.kug.ac.at/o:104384))). However, the MIMO RIRs are not used directly as the representation of the _Directivity_ and _Room Transfer Function_. In a processing stage, the Ambisonic Spatial Decomposition Method (ASDM) [22] is applied to every transducer of the source array; here, the IKO, and the resulting upscaled ASDM RIRs, are eventually used for auralization. This permits a modular exchange of the receiver directivity or HRIRs while keeping the hardware effort at the receiver side minimal. Note that the multi ASDM method is a special form of the SRD ARIR approach, cf. assuming a fixed directivity at the source (the individual loudspeaker) and setting \(N=0\) in Equation (5).