NOISE in a channel
| Collection | International Encyclopedia of Systems and Cybernetics |
|---|---|
| Year | 2004 |
| Vol. (num.) | 2(2) |
| ID | ◀ 2296 ▶ |
| Object type | Discipline oriented |
Any random disturbance originated in the environment which reduces the reliability of a message transmission in a communication channel.
SHANNON'S so-called 10th Theorem states: “If noise appears in a message , the amount of noise that can be removed by a correction channel is limited to the amount of information that can be carried by the channel
This is quite similar to ASHBY's “Law of Requisite Variety ”
Many practical examples are well known, for example in radio, T.V., telephone, fax, etc… transmission.
K. KRIPPENDORFF comments: “The analogy between noise and thermodynamic entropy is suggested by the fact that in any communication process, noise can only increase and it does so at the expense of the amount of information transmitted from a sender to one or more receivers” (1986, p.53).
In some cases, noise disturbances may endanger the functional reliability of parts or even the whole of a system: a lightning may put an electric circuit out of order, or a jumbled message may impair some critical action.
R.L. ACKOFF and F.E. EMERY distinguish semantic, syntactic and pragmatic noise. On this last they write: “Pragmatic noise (is) anything that appears in a message or its environment that was not produced by the sender and decreases the probability of the receiver's responding in the way intended by the sender” (1972, p.182).
T.F.H. ALLEN and T.B. STARR go further and define noise as “Any aspect of a signal string which is not considered significant” (1982, p.274)
Or: “That part of the signal which is not considered to be associated with meaning for the purpose at hand” (Ibid).
The word “considered” introduce (rightly) a doubt, as in this case, either the sender, or the receiver — or both — may well miss something significant in the message only because they do not consider it — or simply do not understand it — to be significant!
It must however be admitted that “significance” is a characteristic of the observer, which moreover, may subtly depend on her/his interpretative ability. BECQUEREL's veiled photographic plates where spoiled by “noise”, until he did understood the correlation with the (radioactive) samples that he had stored in the same drawer, without noticing their peculiar behavior.