Abstract: Difficulty is experienced where filters are required to provide a high level of noise reduction and a fast step response in systems where a large input step in comparison to the final resolution may occur. A suitable filter comprises a variable length averaging filter, an averaging sample counter, the count of which is reduced by a predetermined factor when the count reaches a maximum value, and a spike counter, the count of which is incremented when the difference between an input sample and the current filter output exceeds a predetermined value, the sample count being reset to 1 when the spike count reaches a predetermined value, the filter output being otherwise maintained at the previous output.