 Cutoff frequency

A chosen boundary in a frequency response, commonly where the voltage amplitude gain falls to $1/\sqrt{2}$ of its pass-region value. The convention must specify the reference gain.

The cutoff frequency, often denoted as \( f_c \), is a fundamental parameter in the field of signal processing and filter design. It refers to the frequency at which the output of a filter or a system begins to attenuate significantly compared to its response at lower frequencies. Typically, it marks the boundary between passband and stopband in a filter.