Two‐ear correlation in statistical sound fields

Abstract

The normalized correlation function R (f), connecting the signals at the left and right ears, was measured in a reverberant room as a function of frequency. Head diffraction effects are made evident by comparing these data to the correlation function predicted and observed for two mikes separated by a headwidth (15 cm) of space and moving in the same room. In contrast to the familiar two‐mike sine (δ) correlation (δ — kd), head diffraction gives a two‐ear correlation function, which is well described by sine (αδ)/[1 + (βδ)4]1/2, where α = 2.2 and β = 0.5. The dominant effect of head diffraction is to lower fD, the decoupling frequency [first zero of R (f)], to 500 Hz, about one‐half the no‐head value. The denominator in the fitted correlation function represents the near total independence of the signals at the two ears above fD. Thus, with head diffraction, the variance in a paired‐mike room with averaged pressure amplitude estimate at around 500 Hz, is already as small as that obtained sans head only at frequencies above 1200 Hz. [Work supported by NSF.]