An apparatus, method and computer program is described comprising: receiving a first signal comprising one or more carrier signals comprising a plurality of resource blocks, wherein each resource block is assigned to a unique frequency and time slot of the respective carrier signal; generating a clipping pulse by modifying said first signal; converting the clipping pulse signal into a plurality of narrowband signals, wherein each narrowband signal is a frequency slice of the clipping pulse signal; modifying the plurality of narrowband signals to generate a plurality of modified narrowband signals, wherein said modifying is controlled based on filter weights that define a level of noise to be added to the respective narrowband signals in accordance with a desired error vector magnitude distribution or clipping noise distribution.