Motion reversal invariance in tape recorders

Under certain circumstances, when replaying prerecorded tapes, a reversal of head-tape motion causes a simple time reversal of the output. The occurrence of this phenomenon depends entirely upon the characteristics of the reproduce channel. Motion reversal invariance occurs when the time dependent part of the reproduce channel impulse response displays either of two types of symmetry;in the frequency domain this is equivalent to a quasi-linear phase response.