A method and apparatus adapted to calibrate a signal path of a signal analysis system such that digital samples acquired by the system are processed for representing an arbitrary impedance loading of the 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 reflection coefficient (.GAMMA..sub.L) is defined representative of an arbitrary impedance load coupled to the device under test and an equalization filter is computed to represent the loading of the device under test by the arbitrary impedance. Additional digital samples are acquired using the equalization filter to effect thereby a representation of the arbitrary impedance loading of the device under test.