A method and apparatus for configuring a variable filter in an OFDM transmitter based on the number of subcarrier frequencies selected for the input data block is described herein. An exemplary OFDM transmitter comprises a control unit, OFDM modulator, and variable filter. The control unit selects the number of subcarriers for the input data block, and configures one or more filter properties for the variable filter based on the selected number of subcarriers. The modulator, which has a size greater than the selected number of subcarriers, pads an input data block generated for the selected number of subcarriers to generate an expanded data block having a size equal to the size of the modulator, and modulates the expanded data block to generate an OFDM signal. The filter, as configured by the control unit, filters the OFDM signal.