Signal processing and error control on an experimental high-density digital magnetic tape recording system

The characteristics of a typical magnetic record/playback channel are described, as well as the signal processing and error correction techniques involved in an experimental high-density magnetic recording system. A helical-scan videotape transport is used with direct recording of nonreturn to zero (NRZ) data to 1.1 Mbit/m (20 Mbit/s). The playback receiver includes a fixed prefilter and a seven-tap adaptive transversal filter. System performance can thus be investigated with the assurance of effective equalization under a well-defined tap adjustment algorithm. Performance was monitored as a function of the record level, the number of transversal filter taps, and the head-preamplifier coupling. Raw error rates were typically around 10^-6. Error correction techniques are described which permit a reduction in error rate of several orders of magnitude. The large code spans involved can be significantly reduced by the use of erasure decoding.