A system and method for operating a data processing system to modify a time domain input signal to a signal generator to correct for distortions introduced by the signal generator are disclosed. The method includes receiving a target signal specifying a signal to be generated by the signal generator and initializing an input signal with the target signal, the method includes a) inputting the input signal to the signal generator to arrive at a signal generator output signal; b) measuring a frequency spectrum of the signal generator output signal with a test instrument; c) updating the input signal based on a comparison of said measured frequency spectrum and a frequency spectrum of target input signal; and d) repeating steps a)-c) until an exit condition is satisfied.