Kurzbeschreibung des Projekts

In the context of binaural virtual reality, a sound source is positioned in a 3D space around the listener by filtering it using head-related transfer functions (HRTFs). In a real-time application, a large number of HRTFs needs to be processed. Due to their long impulse responses, this requires a high computational power, which for more than a few simultaneous sources, cannot be implemented directly on current processors.
Technically speaking, an HRTF is a linear time-invariant (LTI) system. An LTI system can be implemented in the time domain by direct convolution or recursive filtering. This approach is computationally inefficient. A computationally efficient approach consists in implementing the system in the frequency domain; however, this approach is not suitable for real-time applications since a very large delay is introduced. A compromise solution of both approaches is given by a family of segmented-FFT methods, which permits a trade-off between latency and computational complexity. As an alternative, the subband method can be applied as a technique to represent linear systems in the time-frequency domain. The project applicant showed in a recent work, that the subband method offers an even better tradeoff between latency and computational complexity than segmented-FFT methods. The subband analysis is still mathematically challenging and its optimum configuration is dependant on the application under consideration.
The project proposal involves developing and investigation of new techniques for configuring the subband method by using advanced optimization methods in a functional analysis context. As a result, an optimization technique will be obtained which minimizes the computational complexity of the subband method especially useful in real-time virtual acoustic applications. Two approaches will be considered: The first approach designs the time-frequency transform for minimizing the complexity of each HRTF. In the second approach, we will design a unique time-frequency transform, which will be used for a joint implementation of all HRTFs. This will permit an efficient implementation of interpolation techniques in the spatialization of moving sources in real-time. The results will be applied to several localization models and evaluated in subjective localization experiments.