The basic principles of symmetric peaks modifications are considered in this work. Four types of modifications--two symmetric and two asymmetric are considered in detail. Double sequent peak modification was taken as example. The dependences of peak shape parameters on modification parameters were obtained for considered examples of modifications of three basic peaks. The methods of obtaining of common sequent modifications and techniques of suitable result function choice for adequate description of analytical signal series are developed. The approximation of groups of stripping voltammetry and chromatographic peaks with some single, double and triple modifications of elementary peaks has been get. The appreciable increasing of adequacy in description of more complicated modifications was shown.