False

The frequency at which the magnitude of the closed-loop frequency response is 3 dB below its zero frequency value is not called the critical frequency. Instead, it is called the cutoff frequency or corner frequency.

Here's an explanation of the correct answer:

Definition of Cutoff Frequency:
The cutoff frequency is a point on the frequency response curve of a system where the magnitude is reduced by 3 dB (half the power) compared to its zero frequency value. It is often denoted as ωc.

Frequency Response Curve:
The frequency response curve is a plot of the magnitude and phase of the system's response as a function of frequency. It provides information about how the system responds to different frequencies.

Explanation:
The critical frequency, also known as the Nyquist frequency, is the highest frequency that can be represented in a discrete-time system without aliasing. It is equal to half the sampling rate.

On the other hand, the cutoff frequency is a characteristic of the frequency response of a system and represents the frequency at which the response starts to roll-off or attenuate.

When the magnitude of the closed-loop frequency response is 3 dB below its zero frequency value, it means that the system's response has been reduced by half the power. This is often used as a reference point to determine the cutoff frequency.

Conclusion:
In conclusion, the frequency at which the magnitude of the closed-loop frequency response is 3 dB below its zero frequency value is not called the critical frequency but the cutoff frequency. The critical frequency is a different concept related to sampling rates in discrete-time systems.

Not critical frequency
false