Filter devices and methods

The invention relates to a filtering method, including: generating a primary filtered signal of an input signal; rounding the primary filtered signal to a primary rounded signal; and combining the primary rounded signal with said input signal for calculating a primary filter error or coded signal. A filtering method is proposed wherein first several filtering steps (I-III, IV-VI) are made. Each step (I-III,IV-VI) includes: generating a filtered signal (I,IV), rounding this filtered signal (II,V) to a certain accuracy and combining (III,VI) the rounded signal with the input signal, whereby a filter error is obtained. The filtered signals are combined (VII) to a first filtered signal that is rounded (VIII) and combined (IX) with the input signal, whereby a coded signal is obtained. This allows to adapt the rounding step (II,V) and the combining step (III,VI) in each filtering step to specific filter design. Thereby limit cycles are reduced, the first filtered signal is available for further processes and the rounding can be inverted in the reverse process. Further a filter method for the reverse process, filter devices () able to perform these methods and devices () containing such devices are provided.