A signal processing system includes: defining a nonlinear function; defining a set of requirements for an output signal; obtaining an input signal; applying a cubic polynomial fitting to approximate the nonlinear function and provide an approximated nonlinear function; assigning a set of fitted polynomial parameters to the approximated nonlinear function; transforming the input signal with the approximated nonlinear function to provide a transformed signal; modifying the transformed signal by adjusting the set of fitted polynomial parameters to provide a modified signal meeting the set of requirements for the output signal; and outputting the modified signal.