**6. Conclusions**

With a specialised measurement setup, acoustic HRTF measurements can be done within a few minutes. Still, such setups are expensive and require the listener to sit or stand still for the whole measurement duration. The requirement of specialised components has been limiting the popularity of the acoustic methods. Recent advances, however, have been made by integrating head-movement tracking in systems to be used at home, especially since the commercialisation of VR headsets. These advances provide an easy-to-use measurement setup, but still need investigation on how many and which measurement positions are crucial to acquire a sufficient measurement grid for perceptually valid HRTFs.

With the availability of numerical HRTF calculations, the acquisition of personalised HRTFs has undergone significant advances. While the acoustic HRTF measurement still remains the reference acquisition method, numerical HRTF calculation paves the road towards personalised HRTFs available for a wide audience. The most widely used approaches, FEM, FDTD, BEM and BEM coupled with the FMM, when applied under optimal conditions, can yield acoustically and perceptually valid results.

Machine learning and neural networks gain increasing popularity and, in the future, may even further push the usability of numerical HRTF calculations. For example, neural networks might be able to support the photogrammetric mesh acquisition or even estimate the HRTFs directly from listener-specific anthropometric data such as photographs. Further improvements in terms of efficiency, accuracy and precision are still ongoing subject of research.

Despite the clear definition when it comes to storing an HRTF data set by means of SOFA, a similar definition for the description of anthropometric data is still not

<sup>1</sup> https://www.sofaconventions.org/mediawiki/index.php/Files

*Perspective Chapter: Modern Acquisition of Personalised Head-Related Transfer Functions… DOI: http://dx.doi.org/10.5772/intechopen.102908*

available. This might be rooted in our poor understanding of the importance of parts of the pinna and its contribution to the HRTF. Here, a clear goal is to better understand the anthropometry and its relation with HRTFs. All this future work heads into the direction of expanding the access to personalised HRTFs enabling their availability for everyone.
