3D Microphone Array Comparison: Objective Measurements

This paper describes a set of objective measurements carried out to compare various types of 3D microphone arrays, comprising OCT-3D, PCMA-3D, 2L-Cube, Decca Cuboid, Eigenmike EM32 (i.e., spherical microphone system) and Hamasaki Square with 0m and 1m vertical spacings of the height layer. Objective parameters that were measured comprised interchannel and spectral differences caused by interchannel crosstalk (ICXT), fluctuations of interaural level and time differences (ILD and ITD), interchannel correlation coefficient (ICC), interaural cross-correlation coefficient (IACC), and direct-to-reverberant energy ratio (DRR). These were chosen as potential predictors for perceived differences among the arrays. The measurements of the properties of ICXT and the time-varying ILD and ITD suggest that the arrays would produce substantial perceived differences in tonal quality as well as locatedness. The analyses of ICCs and IACCs indicate that perceived differences among the arrays in spatial impression would be larger horizontally rather than vertically. It is also predicted that the addition of the height channel signals to the base channel ones in reproduction would produce little effect on both source-image spread and listener envelopment, regardless of the array type. Finally, differences between the ear-input signals in DRR were substantially smaller than those observed among microphone signals.