Phase Distortion

In signal processing, phase distortion or phase-frequency distortion is distortion, that is, change in the shape of the wave worm, that occurs when (a) a filter's phase responses is not linear over the frequency range of interest, that is, the phase shift introduced by a circuit` or device is not directly proportional to frequency, or (b) the zero-frequency intercept of the phase-frequency characteristic is not 0 or an integral multiple of 2π radian.

Audibility of phase Distortion:

Grossly changed phase relationships, without changing amplitudes, can be audible but the degree of audibility of the type of phase shifts expected from typical sound systems 

Human Hearing-Phase distortion Audibility:

pass an audio signal through, for example, a 4th order LR crossover network and view the output on an oscilloscope and the waveform will appear to be a grossly distorted copy of the original.

Pass the same output signal through a spectrum analyzer and the amplitude of the various components will be correct, but their relative phase will have changed. Given the ready availability of software-based spectrum analyzer software and signal generators, investigation of this phenomenon is today almost a trivial exercise in signal analysis.