noise

noise, any signal that does not convey useful information. Electrical noise consists of electrical currents or voltages that interfere with the operation of electronic systems. Electrical noise limits the sensitivity of radio receiving systems and, when present at high enough levels, may cause false outputs from digital circuits. In radio receivers it is important that the noise produced by amplifiers, especially early-stage amplifiers, be kept as low as possible. The signal-to-noise (S/N) ratio is an important factor when evaluating much electronic equipment. Random noise originates when a current flows through a conductor that has resistance and is above absolute zero in temperature. It also arises in electron tubes and semiconductor devices, as well as from atmospheric disturbances and radiation from space (see static). Nonrandom noise originates from the operation of other systems, e.g., automotive ignition systems, and from interfering signals. Noise also affects optical detection systems where light is treated by the particle, or quantum, theory. The output voltage of an optical detector is proportional to the intensity of the incident light. The noise can be from the detectors themselves, the electrical amplifiers that amplify the detector outputs, or thermal noise, which is caused by the vibration of atoms and molecules. Noise can also be inherent in the radiation being detected.

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noise

Undesired sound that is intrinsically objectionable or that interferes with other sounds being listened to. In electronics and information theory, noise refers to those random, unpredictable, and undesirable signals, or changes in signals, that mask the desired information content. In radio, this noise is called static; in television, it is called snow. White noise is a complex signal or sound covering the entire range of component frequencies, or tones, all of which possess equal intensity.

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(1) Extraneous, unwanted signals that invade an electrical or optical system. In electronics, noise can come from strong electrical or magnetic signals in nearby lines, from poorly fitting electrical contacts and from power line spikes. In optics, noise comes from the stray reflections of light that emanate from the various components in the optical system. See signal-to-noise ratio and noise cancellation.

(2) Distortions in analog and digital video images that are caused by a variety of circumstances. The silver grains in the original film create granular noise. Electronic circuits create Gaussian noise. Drop outs and bit errors in digital tapes create impulse noise, and the digitization process creates quantization noise. See Gaussian noise, dynamic noise reduction and artifact.

(3) Distortions in a still image caused by variations in the pixels in the CCD or CMOS sensor. See digital camera.

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(communications)

noise - Any part of a signal that is not the true or original signal but is introduced by the communication mechanism. A common example would be an electrical signal travelling down a wire to which noise is added by inductive and capacitive coupling with other nearby signals (this kind of noise is known as "crosstalk"). A less obvious form of noise is quantisation noise, such as the error between the true colour of a point in a scene in the real world and its representation as a pixel in a digital image.