Analog signal

An analog signal is any continuous signal for which the time-varying feature of the signal is a representation of some other time-varying quantity, i.e., analogous to another time-varying signal. For example, in an analog audio signal, the instantaneous voltage of the signal varies continuously with the pressure of the sound waves.

For broader coverage of this topic, see Signal.

It differs from a digital signal, in which the continuous quantity is a representation of a sequence of discrete values which can only take on one of a finite number of values.[1][2]

The term analog signal usually refers to electrical signals; however, mechanical, pneumatic, 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 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, 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
See also: Comparison of analog and digital recording

An analog signal is subject to electronic noise and distortion introduced by communication channels and signal processing operations, which can progressively degrade the signal-to-noise ratio (SNR). As the signal is copied, transmitted, 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" 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 into the signal due to finite resolution of digital systems, once in digital form, the signal can be stored, processed or transmitted 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

References
  1. Jim Lesurf. "Digital signals". University of St. Andrews. Archived from the original on 2 March 2017. Retrieved 18 February 2018.
  2. "Analog vs. Digital". Sparkfun. 18 February 2018. Archived from the original on 5 July 2017. Retrieved 7 September 2015.
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