In shingled writing, cross-talk noise from an adjacent track occurs when a rather wide track read-head is used, which causes inter-track-interference (ITI). A compensation method has been proposed. However, the linearity of the superposed response from the tracks should be examined for such signal processing. Experimental studies on the superposition of readback waveforms and nonlinearity caused by overwriting of adjacent tracks were carried out. The superposition of the readback waveform was almost precisely maintained. The off-track overwrite performance showed a large track edge over-write noise. Overwrite noise caused by a nonlinear transition shift was also observed.