Marcin Gorzel

HRIR Order Reduction Using Approximate Factorization

A factorization technique is proposed which allows for a direction independent component to be extracted from a set of head related impulse responses (HRIRs). Each individual HRIR is split into a pair of filters, a direction independent component which is common to all HRIRs in the dataset and a direction dependent component which is particular to that HRIR. When these are convolved together, the result is a close approximation to the original HRIR. However, different initial conditions for the factorization algorithm can converge to solutions with drastically different pairs of direction independent and dependent components each of which offer a similarly low reconstruction error. That is, it appears the problem is one with multiple similar local minima. To address the issue of selection of a minimum with psychoacoustic significance the factorization is refined using a regularization technique. Two variants of the regularization are proposed to provide a more robust algorithm that should be less sensitive to the choice initial condition. One of these is suitable for minimum phase HRIR data and allows for very short direction-dependent components to be obtained. The other is suited to initial delay inclusive HRIR data and allows for this initial time delay to be maintained in the direction dependent components. These techniques are applied to HRIR data from the KEMAR and CIPIC databases and the results show low reconstruction error when the original and reconvolved HRIRs are compared. The results of subjective listening tests comparing the performance of factorized and unfactorized HRIRs with truncated HRIRs in an Ambisonic based virtual loudspeaker array are also presented. These suggest there is minimal perceptual difference between factorized and unfactorized HRIRs.

Depth perception of audio sources in stereo 3D environments

In this paper we undertook perceptual experiments to determine the allowed differences in depth between audio and visual stimuli in stereoscopic-3D environments while being perceived as congruent. We also investigated whether the nature of the environment and stimuli affects the perception of congruence. This was achieved by creating an audio-visual environment consisting of a photorealistic visual environment captured by a camera under orthostereoscopic conditions and a virtual audio environment generated by measuring the acoustic properties of the real environment. The visual environment consisted of a room with a loudspeaker or person forming the visual stimulus and was presented to the viewer using a passive stereoscopic display. Pink noise samples and female speech were used as audio stimuli which were presented over headphones using binaural renderings. The stimuli were generated at different depths from the viewer and the viewer was asked to determine whether the audio stimulus was nearer, further away or at the same depth as the visual stimulus. From our experiments it is shown that there is a significant range of depth differences for which audio and visual stimuli are perceived as congruent. Furthermore, this range increases as the depth of the visual stimulus increases.