The issues of digital spectral analysis of signals were considered. The possibility of accurate representation of a complex discrete sequence in the form of a linear combination of multiple harmonics without attenuation has been proved and implemented. A finite algorithm modifying the Prony's method was proposed, with a guaranteed arrangement of the poles of the corresponding autoregressive model on the circle of a unit radius. A scheme of economization of the order of the model in conditions of data redundancy in relation to the estimated limited number of harmonic components of the signal was developed.