The critical frequency of a filter is defined as the point at which the response drops ______ from the pass band.

Critical Frequency:

It is often known as “Cut-off frequency”, and it is also known as the “Corner frequency” or “break frequency”

It is defined as the frequency at which the ratio of output to input has a magnitude of 0.707 of the maximum amplitude.

When converted in decibels it is equal to – 3 dB.

\(Magnitude = 20\log \left( {\frac{{output}}{{input}}} \right)\)

The cut-off frequency is a characteristic of the filtering devices, such as RC circuits.

After this cut-off frequency point, the amount of attenuation due to the filter begins to increase rapidly.

The below figure shows the cut-off frequency of a filter.

∴ At the – 3 dB point, the response drops from the passband.