In science, and especially in physics and telecommunication, noise is fluctuations in and the addition of external factors to the stream of target information (signal) being received at a detector. In communications, it may be deliberate as for instance jamming of a radio or TV signal, but in most cases it is assumed to be merely undesired interference with intended operations. Natural and deliberate noise sources can provide both or either of random interference or patterned interference. Only the latter can be cancelled effectively.
More specifically, in physics, the term noise has the following meanings:
An undesired disturbance within the frequencyband of interest; the summation of unwanted or disturbing energy introduced into a communications system from man-made and natural sources.
A disturbance that affects a signal and that may distort the information carried by the signal.
Random variations of one or more characteristics of any entity such as voltage, current, or data.
A random signal of known statistical properties of amplitude, distribution, and spectral density.
Loosely, any disturbance tending to interfere with the normal operation of a device or system.
Noise and what can be done about it has long been studied. It was Shannon who established information theory and in so doing clarified the essential nature of noise and the limits it places on operation of our (or anyone's) equipment. Shannon's work was a breakthrough.
In some cases a little noise may be considered advantageous, allowing a dithered representation of signals below the minimum strength, or between two quantization levels. This is especially true for signals intended for human appreciation, since the brain seems to expect signals to contain a degree of noise. See, for example [1] (http://www.oreilly.com/catalog/mindhks/chapter/hack33.pdf)
The advantage in raw noise is the ability to see the quality of the generator separate from the cryptographic output.
This is randomnoise, and any one FFT computation can look peculiar; only the average of many such computations gives the (relatively) smooth curve we might at first expect.
The noise source itself was localized (by opening the circuit at various stages) to the first stage, a mixer transistor.
Noise in digital cameras is very different from noise in film, as illustrated in figures 1a and 1b.
The noise floor is determined by the type of read circuits in the image sensor, the transistor characteristics, or imager support circuits such as the analog to digital convertor.
This noise source, known as "photon shot noise", is proportional to the square root of the signal level.
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