Abstract: A high frequency digital synthesizer is provided with aperiodic correction optimizing the spectral plurity, including:a generator of reference clock signals of frequency F.sub.C,a computing device, which, from a frequency increment of the signal to be synthesized, delivers, on the one hand, uncorrected pulses of frequency F.sub.Sj shifted in the time with respect to the signal of frequency F.sub.S to be synthesized by an amount .DELTA.t at most equal to 1/F and, on the other hand, a time error signal corresponding to the shift .DELTA.t and a correction circuit which is initiated by each of the frequency pulses F.sub.Sj for delaying the signal F.sub.Sj by a maximum time when the time error signal is zero by an amount equal to the maximum time reduced by the shift .DELTA.t indicated by the time error signal.