A Multi-tone transmission system processes input data through a plurality of intermediate processing stages 12, 14, 16 and corresponding stages of intermediate data 18, 20. A symbol including a number of tones is obtained therefrom by an inverse Fourier transform 24 and stored in a buffer 158. The peak amplitude that the symbol would contain after the subsequent processing in the analogue front end 146 is modelled and compared to a threshold. If the modelled peak amplitude in the symbol exceeds the threshold, the symbol stored in buffer 158 is regenerated. The symbols stored in the buffer are output through analogue front end 146.