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Nyquist's Law

Definition - What does Nyquist's Law mean?

Nyquist’s law is a formula which states that to accurately represent an analog signal in a digital format, two samples per cycle are sufficient. In other words, the analog signal sampling rate must be at least two times the maximum analog frequency to extract all bandwidth information and accurately represent analog signals in a digital format. Sampling rates that slightly exceed twice the suggested frequency level leads to imprecision in filters and other components used for analog to digital conversion.

Nyquist’s law is also known as Nyquist’s Theorem.

Techopedia explains Nyquist's Law

Before sound can be manipulated on a computer as acoustic energy, it must be converted to electrical energy through the use of a transducer, such as a microphone. The sound then must be converted to a digital representation through an analog-to-digital converter, which is achieved by sampling the continuous input signals a particular number of times per second. A frequently sampled wave results in a more accurate digital representation. For example, human beings cannot hear sounds that range above 20-20,000 Hz (20,000 cycles in one second). To mark sound in an ordinary music CD, analog waves must be sampled at a frequency of 40,000 Hz to re-create a 20,000 Hz signal. The standard CD sampling rate is 44.1 kHz, or 44,100 times per second.

In Japan and North America, Nyquist's law is now the benchmark for using pulse code modulation (PCM) to transform analog sounds to digital formats. A typical 2 kHz voice signal is sampled 4,000 times per second, with each sample transformed into an 8-bit number to produce a 64 Kbps data stream.

Nyquist's law is named after Harry Nyquist, a scientist that discovered the law in 1928.

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