Planarity Analysis of Room Acoustics for Object-based Reverberation

Recent work into 3D audio reproduction has considered the definition of a set of parameters to encode reverberation into an object-based audio scene. The reverberant spatial audio object (RSAO) describes the reverberation in terms of a set of localised, delayed and filtered (early) reflections, together with a late energy envelope modelling the diffuse late decay. The planarity metric, originally developed to evaluate the directionality of reproduced sound fields, is used to analyse a set of multichannel room impulse responses (RIRs) recorded at a microphone array. Planarity describes the spatial compactness of incident sound energy, which tends to decrease as the reflection density and diffuseness of the room response develop over time. Accordingly, planarity complements intensity-based diffuseness estimators, which quantify the degree to which the sound field at a discrete frequency within a particular time window is due to an impinging coherent plane wave. In this paper, we use planarity as a tool to analyse the sound field in relation to the RSAO parameters. Specifically, we use planarity to estimate two important properties of the sound field. First, as high planarity identifies the most localised reflections along the RIR, we estimate the most planar portions of the RIR, corresponding to the RSAO early reflection model and increasing the likelihood of detecting prominent specular reflections. Second, as diffuse sound fields give a low planarity score, we investigate planarity for data-based mixing time estimation. Results show that planarity estimates on measured multichannel RIR datasets represent a useful tool for room acoustics analysis and RSAO parameterisation.