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Harry Nyquist: Why 44.1 kHz Is a Number and Not a Taste

By Infinite Creation · Profile

1889-1976

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At a Glance

Harry Nyquist (1889-1976) established at Bell Labs the sampling condition that bears his name: a signal containing no frequencies above some limit is completely determined by samples taken at more than twice that limit. Shannon later formalised it. It is the reason every digital audio and video sample rate is the number it is.

Lived: 1889-1976, Sweden, worked in the United States
Anchor year: 1928, the sampling criterion
Strand: overlooked, a Bell Labs name in every spec sheet

Career

The problem as it stood

Telegraph engineers needed to know how fast pulses could be sent through a channel of given bandwidth before they smeared into each other. The underlying question, how much information a bandlimited channel can carry, had no rigorous answer.

What he actually did

Nyquist established the relationship between bandwidth and the maximum rate of distinguishable pulses, and the corresponding sampling condition: to represent a signal bandlimited to B, you need more than 2B samples per second.

How it worked

Sample too slowly and frequencies above half the sample rate do not disappear: they fold back into the range below it and appear as false lower frequencies. That is aliasing, and it is irreversible: once folded, the false content is indistinguishable from real content. Hence the anti-alias filter before every analogue-to-digital converter.

What it made possible

All digital audio and video. 44.1 kHz exists because human hearing extends to roughly 20 kHz and a little headroom is needed for the filter. 48 kHz is the professional equivalent. Video sampling, codec design and every converter obey the same constraint.

What happened to him

He spent his career at AT&T and Bell Labs, contributing also to thermal noise theory. Johnson-Nyquist noise, and feedback stability. He retired in 1954 and died in 1976.

Where the credit landed

Nyquist's name survives in the "Nyquist frequency" and the "Nyquist rate", so his attribution is unusually intact, though the theorem is often called Nyquist-Shannon, and the work is Bell Labs work whose patents belonged to the company. Almost nobody who cites the Nyquist rate knows anything else about him.

Known For

Aliasing is irreversible, filter before sampling, not after.
44.1 kHz follows from ~20 kHz hearing plus filter headroom.
The wagon-wheel effect in film is aliasing in the time domain.

Knowledge Base

What You'll Learn

Every digital format in this corpus obeys one inequality.

Why aliasing is worse than losing information

If undersampling simply discarded high frequencies the result would be dull but honest. Instead those frequencies fold down and masquerade as lower ones that were never in the original: a 30 kHz tone sampled at 44.1 kHz appears as 14.1 kHz, audible and wrong. Nothing downstream can remove it, because it is now indistinguishable from real signal. This is why the anti-alias filter is placed before the converter and is not optional.

Where This Fits

Sampling theory decides how any signal is captured digitally, the modern capture link in A History of Broadcast Technology.

FAQ

Q: Why is CD audio 44.1 kHz?
A: Human hearing extends to roughly 20 kHz, so the Nyquist condition requires more than 40 kHz. The extra margin allows a practical anti-alias filter. The precise figure also suited the video recorders used to store early digital masters.

Q: What is aliasing?
A: When a signal is sampled too slowly, frequencies above half the sample rate fold back and appear as false lower frequencies, indistinguishable from genuine content. It cannot be undone after sampling.

Vocabulary

Sampling. Measuring a continuously varying signal at regular intervals and storing each measurement as a number. The step converting a physical waveform into data, and the point where the choice of rate decides what survives.

Sampling theorem. The result establishing that a signal containing no frequencies above a given limit can be reconstructed exactly from samples taken at more than twice that limit. Sets the sample rate of every digital audio format.

Aliasing. The distortion produced when a signal contains frequencies above half the sample rate. Those frequencies do not disappear, they reappear as false lower ones, which cannot be removed afterwards.

Anti-alias filter. A filter removing frequencies above half the sample rate before sampling occurs. Necessary because aliasing has to be prevented at the input, since it is irreversible once recorded.

Sources

The paper was checked against its publication record. Checked 20 August 2026.

H. Nyquist, Certain Topics in Telegraph Transmission Theory. Transactions of the American Institute of Electrical Engineers, volume 47, issue 2, pages 617 to 644, April 1928. Sole author. This is the publication the 1928 anchor year above refers to, twenty years before Shannon formalised the result.