Demodulation of magnetically recorded data

摘要

There is disclosed a pattern matching technique for comparing (a) signals representing detected magnetically recorded characters against (b) a set of predetermined idealized reference signals representing those characters. The pattern matching techniques involves a correlation of coefficients. The characters are encoded as data in the form of binary signals in which one type of bit has a greater width and the other type of bit has a lesser width. Techniques are disclosed to compensate for various distortions in the demodulated characters from the magnetic stripe. These distortions may be due to a loss of magnetic head resolving power, contamination and scratches on the magnetic medium and equipment drift. Techniques are disclosed for normalizing the width of each segment that corresponds to a character. Techniques are also described for detecting the starting point of the segment that represents a character. A technique is described to avoid errors due to abnormal signal peaks.