A method and apparatus adapted to calibrate a signal path of a signal analysis system such that digital samples of a signal under test acquired by the system are processed for representing the impedance of a device under test. The method and apparatus calibrates the signal path to characterize transfer parameters of the device under test within a spectral domain. A reference impedance (Z.sub.ref) is retrieved that is associated with the signal analysis system. The transfer parameters of the device under test and the reference impedance (Z.sub.ref) are processed to effect thereby a representation of the device under test impedance (Z.sub.eq) as a function of frequency.