NOISE CORRELATIONS IN DIBIT RECORDING

Medium noise correlations in dibit data patterns have been studied experimentally in thin film disk/head recording systems. An empirical eigenfunction expansion was utilized to identify the dominant noise modes and possible associated physical mechanisms. At large bit separation where noise power adds linearly, dibit in-phase jitter and out-of-phase jitter were found to be the leading noise modes. The noise waveform shape associated with out-of-phase jitter approaches that of the dibit signals (i.e., this mode of noise becomes amplitude-like) as the bit separation is reduced. In addition, dibit amplitude variation due to the interaction between the two pulses generates the same amplitude-like noise for a small dibit separation. Amplitude mode noise increases as the bit separation is reduced, causing the supralinear noise increase in high recording density. Results from nonlinear amplitude reduction measurement in dibit recording indicate a close correlation between the nonlinearities and the supralinear noise enhancement at high recording density.