Abstract: The invention concerns a digital modulation synthesizer for generating an output frequency or phase modulated radiofrequency signal (SOUT), comprising a pre-accentuation filter (18) receiving a frequency modulation digital signal (Fmod) in input to produce a pre-accentuated frequency modulation signal (F′mod), a modulator &Sgr;-&Dgr; (15) having an input receiving the pre-accentuated frequency modulation signal (F′mod), and an output delivering a pre-accentuated and scrambled frequency modulation signal (Sc), a phase locked loop (PLL) with variable radio frequency divider (14) in the feedback path, the filtering by the phase locked loop (PLL) enabling to filter the quantizing distortion introduced by the modulator &Sgr;-&Dgr; (15) and the pre-accentuation filter (18) applying a pre-accentuation to the frequency modulation signal (Fmod) enabling to compensate the effect of said filtering on the modulation inside a usful band, means for automatic calibration of the pre-accentuation filter (18) enabl