What is Nyquist Frequency? In simple terms, Nyquist Frequency Theory refers to the least number of resolution materials needed for rightly sampling a signal. It can be stated as a kind of sampling frequency, which utilizes signal processing. The utmost frequency over which aliasing will take place is known as Nyquist Frequency.

When it comes to an isolated system for signal processing, it is defined as “Half of the rate”. Above this frequency, the signal with superior frequencies is constructed again in the form of a seismic signal with the least frequencies. It is the utmost frequency that can be coded for a specific sampling rate in such a way that it will become possible to reconstruct the signal. This frequency is otherwise referred to as folding frequency.

Detailed explanation to Nyquist Frequency

At the point of Nyquist Frequency, it will be possible to construct a visual model of a signal. To validate a signal, a couple of samples per cycle are required. This idea is referred to as Nyquist Theorem. Including oversampling and under-sampling, engineers and developers look for problems with sampling. They do this to elevate the testing for signal processing efforts.

Example of Nyquist Frequency

If a speech signal is at 22000 Hz sampling, the utmost frequency that you can anticipate to exist in the sampled signal is 11000 Hz. To observe this anticipation, you should operate the on-going signal through a low-pass filter with a cut-off frequency that is less than 11025 Hz. If not done in this manner, you will come across a phenomenon called aliasing.

Nyquist Frequency in Digital Audio

Nyquist Theorem
Nyquist Theorem: Nyquist sampling (f) = d/2, where d=the smallest object, or highest frequency, you wish to record.

When you take the case of Digital Audio, the frequency is half way the sampling rate. For instance, let us consider that a digital recording uses a rate of sampling of 44.1kHz. The Nyquist frequency, in this case, will be 22.050kHz. In case, the signal that you consider has frequency components that go beyond the Nyquist limit, similar to other areas aliasing will come into picture in digital representation as well. This will happen with an exception. The exception is those frequencies are filtered out before digital encoding.

What if the sample-rate is predetermined?

In the case of instances, where the sample-rate is determined in advance, the filter is selected on the basis of Nyquist Frequency as against vice versa. For instance, when you take the case of audio CDs with a rate of sampling at 44100 samples/sec, the Nyquist Frequency will be 22050 Hz. Here, any greater frequencies should be overpowered using the anti-aliasing filter. However, it can trivially impact the frequencies close to the hearing range of humans. In this case, a filter that can preserve 0-20 kHz will suffice.

Glossary

Nyquist frequency: The utmost likely frequency that you can code in an available sampling rate with a view to be able to fully reconstruct the signal.

Sampling Rate: It is the quantity of samples per second or per any other unit. It is taken from an on-going signal to end up with making a digital or isolated signal.

Anti-Aliasing Filter: It is a filter used prior to the signal sampler for limiting the bandwidth of a signal to entirely or nearly convince the Nyquist-Shannon Sampling Theorem.


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"Nyquist Frequency"

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