A variable-throughput digital modulator receives at an input a transmission digital signal e(t). The transmission digital signal is time-based demultiplexed (1) into first and second elementary transmission signals e1(t) and e2(t) which are applied, respectively, to first (21) and second (22) filtering circuits for delivering first and second filtered elementary signals e1f(t) and e2f(t). A circuit (20) provides throughput switching control to the first and second filtering circuits (21, 22) for selecting a first or second filtering mode corresponding to a first throughput at a first type of modulation or a second throughput at a second type of modulation. A quadrature modulator (3) receives the first and second filtered elementary signals in order to modulate an RDS-compatible carrier f0, and an output filter circuit (5) delivers a filtered modulated carrier signal for broadcast, such as in supplementary data broadcasting in FM radio broadcasting.