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, which may be a video, audio or volumetric 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, at least one quantisation parameter useable in performing quantisation on data based on the first time sample of the signal is determined. The quantisation parameter may indicate one or more levels of quantisation, where a level of quantisation is inversely proportional to an associated measure of similarity. Output data is generated using the at least one quantisation parameter. Preferably, a position of the second data element is the same as a position of the first data element. The method may be appli
