Towards a head-movement-aware measurement of the spatial impression of audio.

This research aims ultimately to develop objective hearing models that can predict the attributes of sound in a similar way to how listeners actually perceive and evaluate it. The research reported in this thesis seeks to determine the nature of head movements in the analysis of spatial impression and to incorporate these into a system for measuring, in a perceptually accurate and appropriate manner, the acoustic parameters which contribute to spatial impression - interaural time and level differences (ITD and ILD), and interaural cross-correlation coefficient (IACC). A review of previous work showed that head movements are known to be used in and beneficial to judgments of source location, but that no information exists yet about head movements in judgments of spatial impression. A consequent experiment showed that the amount of head movement was larger in the evaluation of spatial impression than in localisation and in timbre judgment. In addition, the range of ear orientations was found to form a sloped area, higher to the rear and lower to the front. These findings led to the design of a binaural signal capture and measurement technique using a sphere with multiple microphones which, in comparison to a rotating Head And Torso Simulator (HATS), had the potential for improved measurement speed and the capability to measure time varying systems, potentially at the expense of some accuracy. Performance comparisons between the sphere model, initially with two microphones, and the HATS revealed that differences in ITD and ILD were not perceptually negligible but that differences in IACC were. Suitable post-processing, however, made the sphere with a torso attached valid as a prediction model of both source direction and spatial impression. Reliable derivation of ITD, ILD and IACC at any required ear position was shown to be possible with a limited number of microphones through an appropriate interpolation and calculation technique. A measurement system using a sphere with torso, with 21 omnidirectional microphones on each side placed 10° apart from each other over the sloped ear coverage area, will enable perceptually reliable ITD, ILD and IACC measurements or interpolation for frequencies up to approximately 1kHz