A continuous or ongoing binaural difference in the phase of a sound wave arising from the fact that the peaks arrive momentarily sooner at the nearer ear than the further ear. It is used in conjunction with transient disparity as a cue (2) for localization of sounds below about 1,000 hertz (about two octaves above Middle C) that have wavelengths longer than the diameter of the head, bending round the head rather than being absorbed or reflected by it, and that therefore do not cast sonic shadows on the side further from the sound source. It is one of the binaural time differences or interaural time differences used in sound localization. Also called phase difference, ongoing disparity, or ongoing time disparity. See also binaural shift, biosonar, cone of confusion, sound localization.