A method for determining input tones required to produce a desired output includes the step of extracting a linearization of a spectral map representing a device under test (DUT) that i) is under drive of a large signal having one or more fundamental frequencies with associated amplitudes and phases, and ii) produces an approximation of a desired output having at least one unwanted spectral component. The method includes the further step of using an inverse of the extracted linearization to determine the input tones required to produce the desired output under a given load condition.