Recently, in the field of nonlinear optics of the terahertz frequency range, numerous unique features have been discovered that distinguish it advantageously from nonlinear optics of the optical frequency range. This study demonstrates that the interference of radiations generated at triple frequencies and those due to self-phase modulation in a cubic nonlinear medium can be either constructive or destructive, depending on the parameters of the pulse at the input of the medium. As a result, for a single-cycle pulse, mutual attenuation of these effects is observed by a factor of 20, while for a single and a half-cycle pulse, mutual enhancement occurs by a factor of 1.7. The obtained features are in good agreement with existing experimental data. Thus, by varying the parameters of few-cycle terahertz waves, it is possible to control the nonlinear processes observed in optical media. This will allow for the future development of light-to-light control devices based on these principles.