Estimation of nonlinear distortion using digital higher-order spectra and Volterra series

The concept of linear and nonlinear coherence functions is utilized to evaluate the second- and third-order distortion of a time-invariant nonlinear system, which can be represented by a Volterra series up to the third order, without assuming a Gaussian input. The proposed approach considers the most significant nonlinear distortion products (second-order harmonic, third-order harmonic, second-order intermodulation, and some forms of third-order intermodulation distortion), which are typical in audio components such as loudspeakers, to obtain relatively accurate estimates with reasonable data requirements and computational complexity. This method has been applied to a loudspeaker at low frequencies to model and qualify the linear response, second-order distortion, and third-order distortion