A method of operating an apparatus, the apparatus comprising a prime mover and a plurality of hydraulic actuators (11, 16, 18), a hydraulic machine having a rotatable shaft (4, 30) in driven engagement with the prime mover and comprising a plurality of working chambers having a volume which varies cyclically with rotation of the rotatable shaft, a hydraulic circuit extending between a group of one or more working chambers (10A, 10B) of the hydraulic machine and one or more of the hydraulic actuators, each working chamber of the hydraulic machine comprising a low-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold (6, 54) and a high-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a high-pressure manifold (22, 22A, 22B, 22C, 58), the hydraulic machine being configured to actively control at least the low-pressure valves of the group of one or more working chambers to select the net displacement of hydraulic fluid by each working chamber on each cycle of working chamber volume, and thereby the net displacement of hydraulic fluid by the group of one or more working chambers, responsive to a demand signal, the method comprising controlling the said valves to cause each working chamber to carry out either an active or an inactive cycle of working chamber volume during each cycle of working chamber volume, characterised in that the fraction of working chambers which carry out active cycles is variable and is selected from of a plurality of discrete fractions, wherein the plurality of discrete fractions are selected to avoid generating any repeating patterns of active and inactive cycles of working chamber volume with a length greater than a predetermined maximum repeat pattern length. a hydraulic circuit extending between a group of one or more working chambers (10A, 10B) of the hydraulic machine and one or more of the hydraulic actuators, each working chamber of the hydraulic machine comprising a low-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold (6, 54) and a high-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a high-pressure manifold (22, 22A, 22B, 22C, 58), the hydraulic machine being configured to actively control at least the low-pressure valves of the group of one or more working chambers to select the net displacement of hydraulic fluid by each working chamber on each cycle of working chamber volume, and thereby the net displacement of hydraulic fluid by the group of one or more working chambers, responsive to a demand signal, the method comprising controlling the said valves to cause each working chamber to carry out either an active or an inactive cycle of working chamber volume during each cycle of working chamber volume, characterised in that the fraction of working chambers which carry out active cycles is variable and is selected from of a plurality of discrete fractions, wherein the plurality of discrete fractions are selected to avoid generating any repeating patterns of active and inactive cycles of working chamber volume with a length greater than a predetermined maximum repeat pattern length.