Gradual reinforcement of HRTF symmetries by suitable spherical interpolation

Individual head-related transfer functions (HRTFs) allow for a very accurate rendering of three-dimensional audio scenes via headphones. Given the high spatial resolution necessary for good localization results, a set of HRTFs usually comprises a large number of impulse responses (FIR filters), one for every measured direction. This leads to a very long measurement duration because every acoustic path has to be measured seperately. On the other hand, the rendering of the measured data, specifically in real-time, is a very challenging task in terms of computing power.

In this diploma thesis two basic questions shall be adressed:

Is it possible to reproduce the required high spatial resolution from a lower resolution by a problem specific interpolation method?

How can the well-known slightly symmetrical characteristics of human sound localization be exploited for the compression of HRTF data?

Both of these questions shall be resolved using an adapted spherical harmonic transform which provides a continuuos representation of the HRTF filters in space and also facilitates a choice of the degree of asymmetry permitted. In doing so, suitable HRTF features that are to be interpolated, e.g. time-delay and attenuation, deserve some notice as to avoid undesired artifacts.

The approach shall be evaluated via psychoacoustical tests.

The results of this work are expected to be useful concerning future methods of measuring as well as of rendering of the HRTFs.