There is disclosed a radio receiver, and a filter (24) which may be used in a radio receiver, in which received signals are applied to a digital filter twice, with an intermediate time reversal. This has the effect that any phase distortion introduced by the filter is cancelled by the application of the time inverted signal to the filter. This means that a non-linear filter can be used. Specifically, in preferred embodiments of the invention, an IIR wave digital filter (40) can be used, which means that the device can have lower power consumption and requires a smaller silicon area than would otherwise be the case.