In one embodiment, a drive waveform generator to control ejection of liquid from a set of ejection elements in single-pass printing. A first waveform source defines a first aspect of a drive waveform for the set of ejection elements and for other ejection elements. A second waveform source defines a second aspect of the drive waveform for the set of ejection elements but not for the other ejection elements. A circuit uses the first waveform source and the second waveform source to generate the drive waveform having the first and second aspects.