# ChatGPT – What is Nyquist frequency?

ChatGPT odgovor za ‘What is Nyquist frequency’. (15.9.2023)

The Nyquist frequency, also known as the Nyquist rate or Nyquist limit, is a fundamental concept in digital signal processing and telecommunications. It is named after the American engineer Harry Nyquist. The Nyquist frequency is defined as one-half of the sampling rate or the highest frequency that can be accurately represented or reconstructed in a digital signal or sampled data.

Here’s a more detailed explanation:

1. **Sampling and Digital Signals:** In many real-world applications, continuous signals (analog signals) need to be converted into a digital format for processing and transmission. To do this, the continuous signal is sampled at discrete time intervals, resulting in a series of discrete data points.

2. **Sampling Rate:** The sampling rate, often denoted as “Fs,” is the number of samples taken per second. It is typically measured in Hertz (Hz). A higher sampling rate means more samples are taken per second, providing a more accurate representation of the original signal.

3. **Nyquist Frequency:** The Nyquist frequency (fN) is exactly half of the sampling rate (Fs/2). Mathematically, it is expressed as:

fN = Fs / 2

In other words, the Nyquist frequency is the maximum frequency that can be accurately represented or reconstructed from the sampled data without introducing aliasing.

4. **Aliasing:** Aliasing is an undesirable phenomenon that occurs when a signal contains frequencies higher than the Nyquist frequency, and those frequencies are incorrectly represented as lower frequencies in the digital signal. This can lead to distortion and misinterpretation of the data.

To avoid aliasing, it is essential to ensure that the Nyquist frequency is greater than the highest frequency component of the analog signal you are trying to sample. This is often achieved by selecting an appropriate sampling rate.

For example, consider audio signals. The human hearing range typically extends up to about 20,000 Hz (20 kHz). To accurately capture audio signals, audio systems often use a sampling rate of 44.1 kHz or 48 kHz, ensuring that the Nyquist frequency is above the 20 kHz limit.

In summary, the Nyquist frequency is a critical concept in digital signal processing and sampling theory. It defines the maximum frequency that can be accurately represented in a digital signal without introducing aliasing. Choosing an appropriate sampling rate based on the Nyquist frequency is essential to accurately capture and reproduce analog signals in digital systems.