Method of generating a gradient flow having a constant compositional noise characteristic

Generating a flow having a composition gradient, such as a mobile phase gradient for liquid chromatography, by initiating a plurality of pump strokes from a first pump and at least one additional pump contributing respective first and additional liquids A, B, such as solvents, to the composition gradient of the flow, the volume contributions of each pump changing with respect to time and a sum of the volume contributions of each pump contributed between consecutive initiations of the first pump being constant throughout the duration of the predetermined composition gradient. The stroke frequencies of the pumps may be constant throughout the duration of the gradient or may vary with respect to time for at least one of the pumps. The initiations of the first pump and the additional pumps may be interspersed. Also claimed is a pump system comprising a processor and preferably a mixer, and a computer programme product.