Digital servo system with moving average filter

The invention relates to a method and an arrangement for a digital servo system with moving average filter (Amovavf 1, Amovavf 2),which is used as an input filter for a digital signal processor of the servo system to shorten processing delay, which improves the stability of the control loop and/or allow a fast servo signal processing, which improve the overall servo signal control performance. Said input filter provides average values of samples provided from an analog digital converter (ADC) at a frequency corresponding to a sample frequency (fADC) of the analog digital converter (ADC) and has an adjustable filter length (n), which is determined according to a quality of detector signals indicating a deviation from a target of servo means of the servo system. The invention is e.g. applicable for a fast digital servo system in an optical disc drive.