Nonminimum-phase equalization and its subjective importance in room acoustics

This paper investigates the perceptual significance of residual phase distortion due to an approximate equalization of the nonminimum-phase room response from a sound source to a microphone in a reverberant room. It is shown that disrupted phase relationships introduced by a minimum-phase equalization filter may have a detrimental effect on perceived sound quality. The subjective assessment of phase distortion on speech signals is related to an objective error criterion, newly introduced in this paper. An alternative approach to the minimum-phase/all-pass decomposition based on iterative flattening of the room transfer function (RTF) magnitude is also presented, which overcomes potential numerical problems and provides more insight into subjective aspects of magnitude and phase equalization in the reduction of acoustic reverberation. Factors contributing to the results and practical implications for equalization are discussed.