Characterization and measurement of nonlinear bit shifts in digital magnetic tape recording

Nonlinearities (such as nonlinear bit shifts) are characterized in the form of nonlinear responses by Volterra series expansion. A least-squares procedure is developed to identify the linear and nonlinear responses simultaneously from measurements of the read-head response to some pseudo-random sequences written on tape. A number of experiments have been performed using a helical scan system at different drum speeds. Different MIG heads and metal evaporated (ME) and metal particle (MP) tapes have been used and different write-current levels have been tried out. The authors identifies nonlinear bit shifts quantitatively and shows that the most significant part of nonlinearities can be modelled by just a few parameters. From his measurements, he concludes that nonlinear bit shifts increase with increasing bit density, data rate and write current rise-time