Abstract: Apparatus and method for measuring the impedance of oscillatory systems, or elements of such systems, which exhibit nonlinear behavior at high excitation amplitudes. Excitation of the element being tested, which element may be either acoustical, electrical, or mechanical, is in the form of a combination of a high-intensity biasing signal having a broadband spectrum, and a low-intensity pure sinusoidal tracer signal. The tracer signal is retrieved at an appropriate measuring point in the test system by means of highly-selective filtering. Although the broadband signal comprises the real or basic test signal input to the test element, the retrieved tracer signal is substituted therefor for the purpose of deriving the element's impedance through the use of conventional impedance algorithms. Algorithm solutions thus provided correspond to the response of the element to the entire spectrum of the broadband excitation.