A random profile of transitions in magnetization on thin-film media causes fluctuations of transition-region widths and locations. The readback transducer reacts to an averaged derivative of magnetization, and this results in modulation of magnetization derivative pulses, in shape and amplitude as well as in position (jitter). Due to bandwidth limitations in the readback transducer the high-frequency sideband of the modulation is almost totally suppressed. Thus, readback filtration converts a double-sideband write-cycle modulation into a single-sideband readback modulation.