A process for actuation of multi-level digital modulation, and in particular QAM modulation, by using a single microprocessor is described. The process calls for synchronism of all the frequencies in play. The symbols of the "in phase" and "in quadrature" channels and are oversampled and appropriately digitally filtered. A digital carrier is QAM modulated simply by selecting in string the symbols belonging to the digitally filtered channels taken with their true or negated value. These symbols are then sent to a digital/analog converter followed by a reconstruction filter to obtain the corresponding QAM modulated analog carrier.