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Closed form expressions have been obtained for the power density spectra of signal waveshapes in use for digital magnetic recording. The ``signal'' is the magnetization versus distance profile imposed on the magnetic medium to encode binary ones and zeros. Two general classes of signals are distinguished in terms of neighboring bit-to-bit correlation. Standard recording methods such as saturation NRZ and phase modulation are considered, as well as techniques requiring bias current, such as sinusoidal frequency-shift modulation. The spectra are compared with frequency response curves for the reading head at several recorded bit densities. The more ideal bandwidth characteristics of the newer phase- and frequency-modulation techniques help to explain their improved performance at high bit densities.
Date of Publication: Dec. 1967