A controller for a communications device, comprising: a receiver arranged for receiving a first data block and a second data block, each data block comprising a plurality of analogue signals; a digitizer arranged for converting each analogue signal into a digital value and marking each digital value as saturated when the digital value exceeds a digital range; and a processor arranged for modifying at least one digital value of the first block by combination with a corresponding digital value of the second block except where the digital value of the first block is marked as saturated and marking each modified value as saturated when the modified value is outside a defined range.