Abstract: The invention relates to a method for a unique control of the frequency and utput power of a digital generator, in particular for an ultrasonic welding process. Based on a digital processing, the method according to the present invention compensates not only for variations of the resonant frequency in a broad range, but further provides to control a shifting of the resonant point during the welding process in response to temperature or pressure variations. Power variations caused by variations of the line supply voltage or by the pressure are detected and levelled out by the software. The software monitors the overall operation of in-line machinery, matches its parameters and monitors the complete cycle. The software further ensures an optimum efficiency and effectively protects the end stage against stress caused by high-reactive currents.