The high frequency part of the voiced speech signal beyond 4 kHz is very difficult to study and to decompose into harmonics. In the HNM this spectrum part is assumed to be noise. In this paper it is shown that the main problem is numerical. Faster harmonics have faster trends. It is necessary to implement precise estimation technique to estimate a high frequency complex amplitude on a short time interval. An illustrative example is supplied. In the second part of the paper a new modification technique is proposed for interpolation of the complex amplitudes in the case of intonation modification. Reliable estimates of harmonic complex amplitudes are necessary as inputs. Then a nonlinear rule is formulated that incorporates specific features of formants and their slopes.