An '''analog''' or '''analogue''' [[Wiktionary:signal|signal]] is any time [[continuous function|continuous]] signal where some time varying feature of the signal is a representation of some other time varying quantity. It differs from a [[digital signal]] in that small fluctuations in the signal are meaningful. Analog is usually thought of in an [[electricity|electrical]] context, however [[Classical mechanics|mechanical]], [[pneumatic]], [[hydraulic]], and other systems may also convey analog signals.

An analog signal uses some property of the medium to convey the signal's information. For example, an [[aneroid barometer]] uses rotary position as the signal to convey pressure information. Electrically, the property most commonly used is [[voltage]] followed closely by [[frequency]], [[Current (electricity)|current]], and [[electric charge|charge]].

Any information may be conveyed by an analog signal, often such a signal is a measured [[response]] to changes in physical phenomena, such as [[sound]], [[light]], [[temperature]], [[position]], or [[pressure]], and is achieved using a [[transducer]].

For example, in sound recording, fluctuations in air [[pressure]] (that is to say, [[sound]]) strike the diaphragm of a [[microphone]] which causes corresponding fluctuations in a voltage or the current in an electric circuit. The voltage or the current is said to be an "analog" of the sound.

Since an analogue signal has a theoretically infinite resolution, it will always have a higher resolution than any digital system where the resolution is in discrete steps. In practice, as analogue systems become more complex, effects such as non linearity and noise ultimately degrade analogue resolution such that digital systems surpass it. In analogue systems it is difficult to detect when such degradation occurs, but in digital systems, degradation can not only be detected, but corrected as well.

==Disadvantage==
The primary disadvantage of analog signaling is that any system has [[Noise (physics)|noise]] – i.e., random variation. As the signal is copied and re-copied, or transmitted over long distances, these random variations become dominant. Electrically, these losses can be diminished by shielding, good connections, and several cable types such as [[Coaxial cable|coaxial]] or [[twisted pair]].

The effects of [[signal noise|noise]] make signal loss and distortion impossible to recover, since amplifying the signal to recover attenuated parts of the signal amplifies the noise as well. Even if the resolution of an analog signal is higher than a comparable digital signal, in many cases, the difference is overshadowed by the noise in the signal.

==Modulation==
Another method of conveying an analog signal is to use [[modulation]]. In this, some base signal (e.g., a [[sinusoidal]] [[carrier wave]]) has one of its properties modulated: [[amplitude modulation]] involves altering the amplitude of a sinusoidal voltage [[wave]]form by the source information, [[frequency modulation]] changes the [[frequency]]. Other techniques, such as changing the [[phase (waves)|phase]] of the base signal also work.

[[Analog circuit]]s do not involve [[quantisation]] of information into digital format. The concept being measured over the circuit, whether sound, light, pressure, temperature, or an exceeded limit, remains from end to end.

[[Clock]]s with hands are called analog; those that display digits are called digital. However, many analog clocks are actually digital since the hands do not move in a smooth continuous motion, but in small steps every second or half a second, or every minute.

See [[digital]] for a discussion of ''digital vs. analog''.

Sources: Some of an earlier version of this article was originally taken from [[Federal Standard 1037C]] in support of [[MIL-STD-188]].

[[Category:Analog circuits]]
[[Category:Electronic design]]

==See also==
* [[Analog device]]
* [[Analog sound vs. digital sound]]
* [[Attenuation distortion]]
* [[Digital signal]]
* [[Analog signal processing]]
{{unreferenced|date=August 2007}}

[[ar:إشارة تماثلية]]
[[da:Analog]]
[[de:Analogsignal]]
[[et:Analoogsignaal]]
[[es:Señal analógica]]
[[eo:Analoga]]
[[fa:سیگنال آنالوگ]]
[[fr:Analogique]]
[[ko:아날로그]]
[[it:Analogico]]
[[hu:Analóg]]
[[nl:Analoog]]
[[ja:アナログ]]
[[pl:Sygnał analogowy]]
[[pt:Sinal analógico]]
[[ru:Аналоговый сигнал]]
[[fi:Analoginen]]
[[sv:Analog signal]]
[[zh:模拟信号]]