Dmitry Stepanenko learned a new to him field of the speech signals modelling together with their spectral properties during the last year. He studied some features of sonants. Then Dmitry was asked to solve a problem of interpolation of transfer functions of the vocal tract that generate various allophones. He selected and read modern literature on the linear spectral pairs. Then he proposed his own method of interpolation that appeared to be effective and was highly appreciated by phonetists. Then Dmitry studied accuracy of the formant approximations by roots of linear spectral pairs that is a new result. Dmitry has shown himself as a self-independent and interested researcher that has completed the work on a high level. I think the work is be the estimated as “excellent”.