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Harmonic Distortion Measurement for Nonlinear System Identification

In order to model nonlinearities in loudspeakers, accurate measurement of harmonic distortion is necessary with particular attention to the relative phases of fundamental and harmonics. This paper outlines several ways that logarithmic sweeps can be used to achieve this goal. It is shown that Novak’s redesign of the logsweep is not strictly necessary, if proper account is taken of the phase relationships of the various harmonics. We study several other types of sweeps and methods to extract precise harmonic amplitudes and phases, using tracking filter concepts. The paper also deals with measurement systems that may have fractional-sample delays between excitation, reference, and data channels. Such details are important for accurate phase characterization of transfer functions. An intermodulation example is given for which sweeps with a single instantaneous frequency are inadequate.

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