Noise
Overview
 
In common use, the word noise means any unwanted sound
Sound
Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing and of a level sufficiently strong to be heard, or the sensation stimulated in organs of hearing by such vibrations.-Propagation of...

. In both analog and digital electronics, noise
Noise (electronics)
Electronic noise is a random fluctuation in an electrical signal, a characteristic of all electronic circuits. Noise generated by electronic devices varies greatly, as it can be produced by several different effects...

 is random unwanted perturbation to a wanted signal; it is called noise as a generalisation of the acoustic noise ("static") heard when listening to a weak radio
Radio
Radio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...

 transmission with significant electrical noise. Signal noise is heard as acoustic noise if the signal is converted into sound (e.g., played through a loudspeaker
Loudspeaker
A loudspeaker is an electroacoustic transducer that produces sound in response to an electrical audio signal input. Non-electrical loudspeakers were developed as accessories to telephone systems, but electronic amplification by vacuum tube made loudspeakers more generally useful...

); it manifests as "snow
Noise (video)
Noise, in analog video and television, is a random dot pattern of static displayed when no transmission signal is obtained by the antenna receiver of television set and other display devices...

" on a television
Television
Television is a telecommunication medium for transmitting and receiving moving images that can be monochrome or colored, with accompanying sound...

 or video
Video
Video is the technology of electronically capturing, recording, processing, storing, transmitting, and reconstructing a sequence of still images representing scenes in motion.- History :...

 image.
Quotations

A sound does not view itself as thought, as ought, as needing another sound for its elucidation, as etc.; it has not time for any consideration--it is occupied with the performance of its characteristics: before it has died away it must have made perfectly exact its frequency, its loudness, its length, its overtone structure, the precise morphology of these and of itself.

John Cage (1955), quoted in Classic Essays on Twentieth-Century Music, ISBN 0028645812

Music has no subject beyond the combinations of notes we hear, for music speaks not only by means of sounds, it speaks nothing but sound.

Eduard Hanslick, quoted by Wolfgang Sandberger (1996) in the liner notes to the Juilliard String Quartet's Intimate Letters. Sony Classical SK 66840.

You know the sound of two hands clapping; tell me, what is the sound of one hand?

Hakuin Ekaku (1686-1769). The phrase is a Kōan|Kōan, an irrational comment used in Zen|Zen Buddhism in order to assist practitioners in reaching enlightenment.

Could we not imagine that noise...is itself nothing more than the sum of a multitude of different sounds which are being heard simultaneously?

Jean-Jacques Rousseau, Dictionnaire de Musique (1767)

If a tree falls in a forest, and no-one is around to hear it, does it make a noise?

Source unknown, but apparently originating in the twentieth century; a 1910 physics book asks "When a tree falls in a lonely forest, and no animal is near by to hear it, does it make a sound? Why?" Charles Riborg Mann, George Ransom Twiss, Physics (1910), p. 235. See also: If a tree falls in a forest|If a tree falls in a forest.

 
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