Which of the following parameters requires a calculation using the 20 log function to determine a change in decibels?

The 20 log function is specifically used to calculate changes in decibels for quantities that are proportional to voltage or current. When measuring voltage in relation to a reference value, the formula involves the 20 log of the ratio of the voltage levels. This is because changing the voltage affects the perceived loudness or the level of an audio signal in a way that is logarithmic, meaning that for every doubling of voltage, there is an increase in decibels.

In contrast, power measurements, which are often expressed in decibels, follow a different calculation using the 10 log function since power is proportional to the square of voltage. Frequency does not directly relate to the decibel scale as it deals with the rate of oscillation, while resistance is a measure of opposition to current flow and isn't calculated using decibels.

Thus, when assessing voltage, one uses the formula involving the 20 log function to accurately reflect how changes in voltage are perceived in the context of decibels.