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Swept-sine is a technique for characterizing the frequency response of a device under test (DUT). Two techniques are commonly used in swept-sine measurements. The first technique sweeps through a range of frequencies in a manner similar to a chirp. The following front panel shows an example of the excitation signal for a sweeping swept-sine measurement.

The second technique steps through a range of frequencies. The following front panel shows an example of the excitation signal for a stepping swept-sine measurement.

The swept sine implemented in the NI Sound and Vibration Measurement Suite generates an excitation signal that steps through a range of test frequencies, similar to the signal in the previous front panel. The sweeping swept-sine measurements and the stepping swept-sine measurements can yield similar results. However, they require very different measurement analysis processes.

Swept-sine frequency-response measurements compare a response signal to the stimulus tone in order to compute the frequency response function (FRF) of the DUT. The magnitude of the FRF is equivalent to the gain and represents the ratio of the output level to the input level for each test frequency. The phase of the FRF is equivalent to the phase lag introduced by the DUT for each test frequency.

Swept-sine measurements require a signal source. The stimulus signal is always a single tone that excites the DUT at the test frequency. Since the stimulus is a single tone, swept-sine analysis can measure the harmonic distortion while simultaneously measuring the linear response.