Click here to purchase the entire book in PDF format. Gain Linearity In theory, a DUT should have the same gain on a signal irrespective of the level of the input (assuming that we're not measuring a DUT that is supposed to make dynamic gain changes, like a compressor, limiter, expander or gate, for example...). Therefore, the gain, once set to a value of 2 using a 0 dBV 1kHz sine tone should be 2 for all other amplitudes of a 1 kHz sine tone (it may change at other frequencies, as in the case of a filter, for example, but we'll come to that...) If this is indeed the case, then the DUT is said to have a linear gain response. This will likely not be the case - so we measure the gain of the DUT using various amplitudes at its input. The resulting measurement is most easily graphed on an X-Y plot, with the input amplitude on the x-axis and the deviation from the nominal gain on the y-axis. This measurement is useful for showing the distortion of low-level signals caused by digital converters in a DUT, for example.