The article examines the predictability of Russian verbal modifications during the process of word formation synthesis. The main reasons for modifiers' combinatorial irregularity with respect to semantically connected sound verbs are identified. For the first time ever, the sound source, as the primary factor in determining the word formation synthesis' results, is described from three perspectives: semantic, lexicographic, and denotative. Using various parameters relevant for both sound source and semantic modifiers, the sound verbs are subjected to combinatorial testing. The nature of dynamic dependency between the results of word formation synthesis, the distinguishing characteristics of modifiers, and the semantic range of verbs is analyzed.