Median Plane Localization - Psychoacoustics and Spatial Audio Effects

Abstract

This thesis investigates the perception of the elevation of sources in the median plane by monaural spectral cues and, correspondingly, the synthesis of virtual source elevation using audio signal processing techniques.

The contribution of spectral cues to median plane localisation was examined by measuring directional band effects with a more comprehensive approach than in existing literature. Additionally, the ability to segregate two concurrent sound sources in the median plane by spectral cues was examined with subjective listening tests, resulting in a measure of angular differentiation using monaural spectral cues alone. The measure was found to be finer than in an earlier study. The study also investigated the impact of added broadband noise on short sounds on localization in the median plane. The research revealed that, under specific circumstances, introducing background noise before a short sound burst can significantly improve localisation accuracy and mitigate inaccurate front-biased elevation perception in the median plane. A novel method for creating the perception of sound elevation was developed by utilising relative HRTF envelope filters. These filters were produced to examine the effectiveness of macroscopic HRTF envelopes that omitted the fine spectral details of pinna cues. The studies found that robust elevation perception can be achieved through the spectral features found in macroscopic HRTF envelopes as well as directional bands. Moreover, these spectral features were then utilised as the elevation filters by applying them to the early reflection part of stereo room impulse responses, which was subjectively verified to create the vertically extended perception of the reverberant sound field with acceptable colouration. The present thesis thus demonstrates that the macroscopic HRTF envelopes and directional cues can be widely beneficial across individuals diversely; however, individual-specific pinna-related features introduced in HRTFs enable more precise median plane localisation via spectral detail.