Decoder for magnetic stripe recording

A decoder for flux reversal indicia on a magnetic material, said decoder including circuit means responsive to each of said indicia for generating a signal representative thereof, said circuit means including an amplitude differentiator for disabling said circuit responsive to flux reversal indicia on said magnetic material which produce signals which have amplitudes of less than a preset amplitude which is a function of the signal being read, wherein said magnetic material is a magnetic stripe having a sequence of indicia recorded thereon at a density of from about 65 bits per inch to about 430 bits per inch, said indicia comprising positive and negative flux reversals, said decoder also including means responsive to successive indicia pairs of said sequence of said indicia for determining the distance to the next successive flux reversal of opposite polarity, and means for setting positive and negative pulse amplitude threshold levels for discriminating against positive and negative low amplitude pulse levels respectively.