Noise

In general usage, noise can be considered sound without meaning; that is, the sound is not being used to transmit information, but simply is produced as a byproduct of other activities. Most often in general use it is applied to meaningless sound of greater than usual volume. Thus, a loud activity may be referred to as noisy.

In science noise has a more specific meaning; it refers to random fluctuations and the addition of external factors to the stream of target information (signal) being received at a detector. (See signal-to-noise ratio.)

In Goidelic mythology, Noise was the nephew of King Conchobar of Ulster, and a son of Usnech.

Conchobar planned on marrying his step-daughter, the beautiful Deirdre. She fell in love with Noise; they fled to Scotland with his two brothers. Conchobar's messengers asked Noise and his brothers to return to Ireland. They did and he killed them. Deirdre died of grief.

In telecommunication, the term noise has the following meanings:

1. An undesired disturbance within the frequency band of interest; the summation of unwanted or disturbing energy introduced into a communications system from man-made and natural sources.

2. A disturbance that affects a signal and that may distort the information carried by the signal.

3. Random variations of one or more characteristics of any entity such as voltage, current, or data.

4. A random signal of known statistical properties of amplitude, distribution, and spectral density.

5. Loosely, any disturbance tending to interfere with the normal operation of a device or system.

Source: from Federal Standard 1037C and from MIL-STD-188