Perceptibility of double-slope reverberation decays

Abstract

No concert hall has a perfectly diffuse field, although many are close enough that their decay is perceived as linear. In recent years, concert hall acousticians have taken steps to ensure more exaggerated double-sloped (nonlinear) decays in their concert halls by using coupled volumes. Some acousticians feel that a coupled volume gives a hall a balance between clarity (subjectively speaking) and reverberance. However, there have been no studies done to determine when a nonlinear decay becomes perceptibly different from a linear decay. This work seeks to identify the threshold of perception for nonlinear decays. Nonlinear impulse responses of different lengths are generated by first computing uncoupled impulse responses of a concert hall and a coupled volume in CATT-Acoustic. The two linear impulse responses are convolved in matlab. These convolved impulse responses are manipulated to systematically vary the degree of nonlinear decay. The various nonlinear impulse responses are then convolved with anechoic signals with different temporal characteristics and presented to listeners for evaluation. From these evaluations, a criteria is derived to determine when a nonlinear decay becomes audibly different from a linear decay to a listener for various representative signals.