In article the necessity of developing a mathematical model for converting the recorded NMR signal using a modulation technique into the spectrum for new investigations is substantiated. The comparison of various methods for describing the shape of the registration NMR signals to determine the line structure and various practical tasks solve is performed. A mathematical model for to represent the NMR signal in the form of a spectrum, taking into account the features of its registration from condensed matter is developed. Spectra of calculated and experimental NMR signals are presented. Its comparison is carried out.