Frequency Sweep

Swept-sine measurements use two signal-generation techniques: continuous swept-sine measurement and stepped swept-sine measurement. A continuous swept-sine measurement sweeps through a set of frequencies to generate a chirp pattern. The following figure shows an example of the excitation signal for a continuous swept-sine measurement.

In the previous chirp signal, the frequency linearly sweeps with time. In audio applications, you also use chirp signals in which the frequency exponentially sweeps with time.

A stepped swept-sine measurement steps through a set of frequencies. The following figure shows an example of the excitation signal for a stepped swept-sine measurement.

A swept-sine measurement requires an excitation signal. The excitation signal is always a single-tone signal that excites the DUT at the test frequency. A swept-sine measurement can measure harmonic distortion and linear response simultaneously.

A swept-sine measurement compares the response signal from the DUT to the excitation signal 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 that the DUT introduces for each test frequency.