FNyquist

fNyquist is a term used in digital signal processing to denote the Nyquist frequency, typically defined as one-half of the sampling rate. It represents the theoretical upper bound for the frequency content that can be accurately represented in a discrete-time signal. In many texts, fNyquist is used interchangeably with f_N = f_s/2, where f_s is the sampling frequency. The concept arises from the Nyquist–Shannon sampling theorem, which states that a bandlimited analog signal can be reconstructed from its samples if the sampling rate exceeds twice the maximum signal frequency, making fNyquist the highest resolvable frequency in the discrete domain.

In practice, fNyquist is important for tasks such as anti-aliasing filter design, spectral analysis, and digital-to-analog conversion. It helps engineers determine where the discrete spectrum ends and where potential aliasing would begin if higher frequency energy is present. Real-world systems often treat fNyquist as an effective bound that may be slightly lower than the mathematical half of the sampling rate due to non-ideal filter characteristics and transition bands.

Examples: with a sampling rate of 44.1 kHz, fNyquist is 22.05 kHz; with 48 kHz, it is 24 kHz. Signals approaching fNyquist require careful filtering to prevent aliasing and distortion in the reconstructed signal.

See also: Nyquist frequency, sampling rate, aliasing, anti-aliasing filter, Fourier transform.