Image shift caused by strong lateral reflections, and its relation to inter-aural cross correlation

Abstract

Conditions of sound fields were studied to avoid the occurrence of image shift, an acoustical phenomenon caused by extremely strong lateral reflections. Three types of image shift are defined as variations of the normal condition, in which there is only one auditory image perceived in the source direction. From a series of listening tests in electrically reproduced sound fields, each of the three types of image shift was found to have its own specific frequency range in which the image shift occurred. They were also found to relate to each of three measures which are all derived from the inter-aural cross correlation function (IACF) of binaural impulse responses of a sound field. The results of measurement made in three existing concert halls suggested acceptable ranges for the measures, in which the image in the source direction is not lost in the 500 Hz and higher frequency bands. However, the 250 Hz and lower frequency bands were found not so important in evaluating sound fields of concert halls in relation to the image shift. Finally, 0.85 is found to be the upper limit for the preferable range of [1 - IACC(E3)].