A first value of a first data element (311) in a first set of data elements (310) is obtained, the first set of data elements being based on a first time sample of a signal. A second value of a second data element (321) in a second set of data elements (320) is obtained, the second set of data elements being based on a second, later time sample of the signal. A measure of similarity is derived between the first value and the second value. Based on the derived measure, a quantisation parameter useable in performing quantisation on data based on the first time sample of the signal is determined. Output data is generated using the quantisation parameter.