Nyquist Sampling Theorem - Statement, Working, Aliasing, Applications (2024)

Nyquist Theorem also referred to as the Sampling Theorem is a principle of reproducing a sample rate, that is at least twice the frequency of the original signal. This principle is very important in all analog-to-digital conversion and is applied in digital audio and video to minimize a problem referred to as Aliasing.

In digital communication, signals are representations of information that are transmitted from one point to another in a digital format. Nyquist Sampling is a critical theorem that is used to derive the frequency of the signal to reconstruct without aliasing. Aliasing refers to the distortion or unwanted noise that may destroy a signal’s integral value.

What is the Nyquist Sampling Theorem?

It was given by Harry Nyquist Claude, Shannon of Bell Labs first provided the Nyquist-Shannon sampling theorem in the late 1940s. Harry expressed the Nyquist Sampling Theorem which established the principle of using sampling to convert a continuous analog signal to a digital signal. He produced a sample rule that should be followed to determine appropriate sample rates for differing sounds.

It states that to reconstruct a continuous analog signal from its sampled version accurately, the sampling rate must be at least twice the highest frequency present in the signal. This ensures that there are enough samples taken per unit of time to capture all the details of the original waveform without introducing aliasing, which can cause distortion or artifacts in the reconstructed signal.

The Formula for Nyquist Sampling Theorem can be given as

[Tex]f_s >=2f_m[/Tex]

See Also

What is the Nyquist theorem?10.2: Sampling Theorem2.3. The Nyquist-Shannon sampling theorem — Digital Signals Theory

Where,

[Tex]f_s[/Tex] refers to frequency signal

[Tex]f_m[/Tex] refers to max frequency

The Theorem is important in the various fields such as audio and image processing, where analog signals are commonly converted into digital form. By understanding the concept of Nyquist sampling theorem, we can determine the appropriate sampling rates to ensure the accuracy of the digital representation of analog signals.

How Nyquist Sampling Theorem Works?

The Nyquist Sampling Theorem explains the relationship between the sample rate and the frequency of the measured signal. It is used to suggest that the sampling rate must be twice the highest frequency in the signal. It is used to reconstruct any signal from samples. A sample is basically the number of times an analog signal is measured per value of time (typically seconds).

• Relationship Between Sampling Rate and Signal Frequency: T he Theorem States that Sampling rate(fs) should be greater than or equal to the twice the highest frequency component(fm) in the signal.
• Preventing Aliasing: When the Sampling rate is double the highest frequency of the signal, Aliasing can be avoided. Aliasing occurs when the high frequency parts of the signal occurs in the lower frequency, causing distortion.
• Reconstruction of Signals: The Nyquist theorem tells us that if we sample a signal at a rate higher than twice its highest frequency, we can reconstruct the original analog signal from these samples. This is done using methods like interpolation and reconstruction algorithms, ensuring we don’t lose important information from the original signal.
• Concept of Sampling: Sampling is simply capturing the strength of an analog signal at specific moments in time. These captured strengths, or samples, create a digital version of the original signal. So, by taking enough samples, we can accurately represent the analog signal in digital form.

For example, If we were to store sound like music in a CD, the audio signal must be sampled at a rate of at least 40,000 Hz to reproduce the 20,000 Hz signal.

The sampling rate must be at least twice the highest frequency in the signal.

Let

Original frequency be 20,000 Hz

Since fs >= 2fm

The reproduced sample rate must be 40,000 Hz.

Aliasing in Nyquist Theorem

Aliasing in Nyquist Theorem is simply referred to as the unnatural disturbance that may occur during when the signals are reconstructed from one form to another. It may be referred to as the unwanted frequencies in an audio recording or strange patterns in an image or information that is necessarily lost during analog to digital conversion. Jitter noise in audio may be regarded as Aliasing. To fix the problem of aliasing, Nyquist derived this theorem.

Disadvantages of Aliasing

• It leads to noise, which can disrupt a signal.
• It leads to distortion and pixelation of of any signal.
• It disrupts data signal transmission.
• It can lead to degrade the quality of the signal which can lead to loss of data.
• It can interfere with the accurate detection of signals, leading to missed or false detections.
• It can cause misinterpretation of the signal

Characteristics of Nyquist Sampling Theorem

• The Nyquist–Shannon sampling theorem is an essential principle for digital signals to avoid a type of distortion known as Aliasing.
• Sampling is a process of converting a signal into a sequence of digital values.
• Aliasing can be prevented with a variety of anti-aliasing tools, such as low-pass filters that filter out high frequencies.
• The Sampling Theorem states that a signal can be exactly reproduced if it is sampled at a frequency F, where F is greater than twice the maximum frequency in the signal.
• It is also known as the Nyquist-Shannon theorem or the Whittaker-Nyquist-Shannon sampling theorem.
• The sampling theorem is critical to prevent aliasing in a waveform.

Applications of Nyquist Theorem

• Sampling Rate: It is used to provide the minimum sampling rate for signal reconstruction.
• In Audio: It is used to capture analog or simple audio from digital mediums.
• Digital Transmission: It is used to provide accurate digital data transmission in digital mediums.
• Image Sampling: It is quite helpful in image sampling by measuring the twice of original size of Image.
• Reducing Aliasing in Audio Signals: It can successfully reproduce audio signals without aliasing.
• FM Radio Signals: It is used to sample FM radio signals by the nyquist formula.
• Data Compression: It can reduce the size of data without content or information loss.
• Medical Imaging: It is majorly used in medical instruments such as MRI (Magnetic Resonance Imaging) and CT Scans (Computed Tomography), The Nyquist theorem is used to play an important role in finding the sampling rate of the original signal.

Conclusion

In conclusion, Nyquist Sampling Theorem is used to determine the sampling level without aliasing in Digital Communication. It is very important to reproduce any signal without noise, and used in various fields such as Audio and Digital transmission, Radio Signals and FM radio signals. It is mainly used to prevent distortion in Digital audio communication.

FAQs on Nyquist Sampling Theorem

Why is the Nyquist sampling theorem important?

The Nyquist theorem is important because it suggests that sampled signals can be accurately reconstructed without loss of information, aliasing or distortion.

What are some practical applications of Nyquist sampling theorem?

Nyquist Sampling theorem is heavily used in Telecommunication, and fields such as audio and image sampling, digital and signal definition.

What is Sampling Interval?

It is referred to as the time interval between the samples taken from a signal during analog to digital conversion, often referred to as ADC . In simple words, it refers to the time interval at which the signal is measured