Microphone Position Realignment by Extrapolation of Virtual Microphone

Abstract

In this paper, microphone realignment by phase extrapolation using the virtual microphone technique for reproducing binaural signals with adequate the interaural time differences (ITDs) for a listener is proposed. For a sound source in the horizontal plane, ITDs are a major cues for localizing a sound image. Since ITDs are not considered for headphones listening in conventional amplitude panning in multichannel recording, sound images are localized inside the head (lateralization). A microphone array is applicable to recording signals with time differences corresponding to the directions of sound sources. Since microphones in such an array are closely positioned, the time differences are inappropriate as ITDs for localizing sound images for the sources. In this paper, phase extrapolation using the virtual microphone technique is applied to the virtual realignment of a microphone in such an array for restoring ITD. In the experiments with two speeches as sound sources located at the leftmost and the rightmost positions from the viewpoint of two real microphones positioned 2.83 cm apart. Furthermore, the phase of a signal of a virtual realigned microphone is extrapolated eight times as much as the phase between the two real microphones. Time differences between signals of one of the real microphones and the realigned one are observed to be $-500\ \boldsymbol{\mu}\mathbf{s}$ for the source on the left and $500\ \boldsymbol{\mu}\mathbf{s}$ for the source on the right. Furthermore, the interaural cross correlations of the two signals suggest that sound images will be perceived on both the left and right of a listener. In this method, it is expected that prior information on the number of sources and the direction of arrival is not required, and the adjustment of individual differences is easy.