Abstract: Method and apparatus for analyzing the harmonic distortion present in an input signal wherein first and second reference signals are generated differing by a small offset frequency. The first reference signal is mixed with the input signal to provide an intermediate carrier signal which is modulated with the second reference signal to provide a measurement carrier signal which in turn is modulated with the input signal to produce an output signal which is filtered to isolate a specific signal. By isolating a specific signal for each harmonic of the input signal to be analyzed, the proportion of each such harmonic is revealed as a percentage of the fundamental harmonic of the input signal.By adding a tunable oscillator to the apparatus, it may function as a wave analyzer, in which case the specific output signal represents the magnitude of any selected component of the signal to be analyzed.