Dropouts are intermittent losses of signal commonly seen in magnetic tape recording readout. The main reason for such losses is the increased spacing between the head and the medium due to media defects or debris particles. The resulting signal is not only degraded by the apparent amplitude loss, but the characteristics of the pulses due to transitions are also changed. Moreover, in many cases, the locations of the pulses are altered, causing excessive amounts of peakshift. In this paper, a model, linking the liftoff to these effects, is presented. Experimental verification of the model using actual signals from a test tape drive is also given. Artificial dropout waveforms generated using this model are used to test two different read channel strategies. The first approach is an equalization-based correction scheme that attempts to undo the dropout. Results indicate that the dropout effects can be almost completely eliminated if an appropriate equalization procedure is applied. As an alternative approach, it is shown that the use of turbo coding in the presence of dropouts appears to be promising.

We consider the issue of combating signal dropouts in magnetic tape recording. Dropouts are a major limiting factor in the performance of the channel as they cause long bursts of bit errors. To attack this problem, a model of the dropout event has been developed. Based on that model, a strategy has been identified in which an envelope detector followed by a feedforward equalizer is used. The equalization process is done in such a way as to address the three major effects caused by a dropout event: amplitude loss, pulse widening and peakshift. The crucial part of this scheme is the spacing profile estimator, which makes use of an envelope detector. With this scheme, the effects of the dropout are corrected at the expense of a delay in the channel. The model of the dropout and the correction scheme are all presented.