Problems arising from a pre-emphasis filter, particularly an infinite-impulse-response filter, in a signal modulator are solved by detecting sequences of the same bit or symbol in a modulation signal and compensating the corresponding d.c. offset in the signal generated by the pre-emphasis filter without real-time feedback. The amount of offset compensation can be defined during design of the modulator or adjusted or calibrated during production. It is not necessary to change the transfer function of the pre-emphasis filter, but only to correct the d.c. offset of the filter output signal.