The room impulse response in time, frequency, and space: Mapping spatial energy using spherical array beamforming techniques

Abstract

The auditory perception of rooms is a multi-dimensional problem. Our hearing system interprets time, frequency, and spatial information from arriving room reflections, but traditionally, only the time and frequency domains are considered in room acoustic metric and objective sound field analyses. This work aims to develop spatial visualizations of the energy in a room impulse response (RIR). With a spherical microphone array, a room’s energy can be mapped in full three-dimensions. First, beamforming techniques are used to generate a set of directional RIRs from the spherical microphone array measurement. This set of directional RIRs is analogous to using a microphone with a directional beam pattern response, oriented individually at all points around a sphere. Then, these directional or beam RIRs are time windowed and band-pass filtered to create spatial energy maps of the room. Comparisons between a plane-wave beam pattern and a Dolph-Chebyshev beam pattern will be demonstrated in the context of RIR beamforming. As well, different strategies for normalizing peak energy amplitudes to either the direct sound or a spherical spreading condition will be compared. With these considerations, final results of these spatial energy visualizations and directional RIR animations will be demonstrated. [Work supported by NSF Award 1302741.]