When information is written onto a magnetic disc, the information is recorded in digital form. Digital square waves have vertical edges that a magnetic head can sense. Positive and negative transitions in the square wave, that is the edges, are recognized and recorded on the magnetic medium of the disc. When the magnetic head is used to read the data stored on the disc, the output is not in digital form because of the characteristics of the head and the magnetic medium.
It is frequently desirable to locate the vertical edges of the original digital signal initially written onto the magnetic disc. Therefore, the information read from the disc must be manipulated to determine the location of the vertical edges of the original digital signal written onto the disc.
Prior solutions to recreating the vertical edges of original digital signal have concentrated on the recreation of the original digital signal itself. These methods have been based on various forms of zero-crossing detectors to indicate when the applied signal crossed a base line as explained by Batey, et al., in A Method And Means For Direct-Current Polarity Restoration In Magnetic Recording, pending U.S. patent application Ser. No. 365,661 filed Apr. 5, 1982.
However, prior solutions to locating the vertical edges of the original digital signal introduced time delays which required additional circuits for its removal or required isolated positive and negative analog signals which required careful circuit design to prevent differential timing errors.