The paper deals with the analysis of settling phenomena that characterize the step response of digital to analog converters, amplifiers, and several other devices. Settling is described by means of a minimal second order model that is suitable to account for the distortion terms recognized in the signal spectrum. An alternative method for dynamic performance assessment of systems characterized by poor settling performance is then proposed. Thanks to the use of high bandwidth spectrum analyzers, the proposed method overtakes the limits characterizing the measurement approaches based on the use of time-domain instruments in the presence of modern ultra-wideband systems.