An analog signal or analogue signal (see
spelling differences) is any
continuous signal representing some other quantity, i.e., ''analogous'' to another quantity. For example, in an analog
audio signal, the instantaneous signal
voltage varies continuously with the
pressure of the sound waves.
In contrast, a
digital signal
A digital signal is a Signal (electrical engineering), signal that represents data as a sequence of discrete space, discrete values; at any given time it can only take on, at most, one of a finite number of values. This contrasts with an analog ...
represents the original time-varying quantity as a
sampled sequence of
quantized values which imposes some
bandwidth and
dynamic range constraints on the representation.
The term ''analog signal'' usually refers to
electrical signals; however,
mechanical,
pneumatic
Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air.
Pneumatic systems used in Industrial sector, industry are commonly powered by compressed air or compressed inert gases. A central ...
,
hydraulic and other systems may also convey or be considered analog signals.
Representation
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. In an electrical signal, the
voltage,
current, or
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from '' angular frequency''. Frequency is measured in hertz (Hz) which is ...
of the signal may be varied to represent the information.
Any information may be conveyed by an analog signal; such a signal may be a measured response to changes in a physical variable, such as
sound
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by ...
,
light,
temperature, position, or
pressure. The physical variable is converted to an analog signal by a
transducer. For example, sound striking the diaphragm of a
microphone induces corresponding fluctuations in the current produced by a coil in an electromagnetic microphone or the voltage produced by a
condenser microphone. The voltage or the current is said to be an ''analog'' of the sound.
Noise
An analog signal is subject to
electronic noise and
distortion introduced by
communication channels,
recording and
signal processing
Signal processing is an electrical engineering subfield that focuses on analyzing, modifying and synthesizing '' signals'', such as sound, images, and scientific measurements. Signal processing techniques are used to optimize transmissions, ...
operations, which can progressively degrade the
signal-to-noise ratio
Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to the noise power, often expressed in deci ...
(SNR). As the signal is transmitted, copied, or processed, the unavoidable noise introduced in the signal path will accumulate as a
generation loss, progressively and irreversibly degrading the SNR, until in extreme cases, the signal can be overwhelmed. Noise can show up as
hiss
Hiss or Hissing may refer to:
* Hiss (electromagnetic), a wave generated in the plasma of the Earth's ionosphere or magnetosphere
* Hiss (surname)
* ''Hissing'' (manhwa), a Korean manhwa series by Kang EunYoung
* Noise (electronics) or electroni ...
and
intermodulation distortion in audio signals, or
snow in
video signals. Generation loss is irreversible as there is no reliable method to distinguish the noise from the signal.
In contrast, although
converting an analog signal to digital form introduces a low-level
quantization noise
Quantization, in mathematics and digital signal processing, is the process of mapping input values from a large set (often a continuous set) to output values in a (countable) smaller set, often with a finite number of elements. Rounding and t ...
into the signal due to finite resolution of digital systems, once in digital form, the signal can be transmitted, stored, or processed without introducing significant additional noise or distortion.
Noise accumulation in analog systems can be minimized by
electromagnetic shielding,
balanced lines,
low-noise amplifiers and high-quality electrical components.
In analog systems, it is difficult to detect when such degradation occurs. However, in digital systems, degradation can not only be
detected but corrected as well.
See also
*
Amplifier
*
Analog computer
*
Analog device
*
Analog signal processing
*
Magnetic tape
Magnetic tape is a medium for magnetic storage made of a thin, magnetizable coating on a long, narrow strip of plastic film. It was developed in Germany in 1928, based on the earlier magnetic wire recording from Denmark. Devices that use magne ...
*
Preamplifier
References
{{DEFAULTSORT:Analog Signal
Analog circuits
Electronic design
Television terminology
Video signal