This project studies the audibility of phase distortion in audio signals. The transfer functions of linear systems can generally be decomposed into a minimum-phase component, an all-pass component and a pure delay. The audibility of the all-pass component was investigated in a listening test, in which a panel of listeners were presented with signals that only differed from each other in terms of their all-pass sections. Specifically, the audibility of a second order all-pass section was tested with the all-pass section applied to either one channel or both channels. The results are threshold curves for Q as function of centre frequency. Supported by STVF/FTP.