Assessing the anisotropic features of spatial impulse responses

The direction-dependent characteristics of late reverberation have long been assumed to be perceptually isotropic, meaning that the energy of the decay should be perceived equal from every direction. This assumption has been carried into the way reverberation has been approached for spatial sound reproduction. Now that new methods exist to capture the sound field, we need to revisit the way we analyze and render the decaying sound field and more specifically, establish the perceptual threshold of direction dependent characteristics of late reverberation. Towards this goal, this paper proposes the Energy Decay Deviation (EDD) as an objective measure of the directional decay. Based on the deviation of direction-dependent Energy Decay Curves (EDC) to a mean EDC, the EDD aims to highlight the direction-dependent features characterizing the decay. This paper presents the design considerations of the EDD, discusses its limitations, and shows practical examples of its use.