In contrast, adigital signal represents the original time-varying quantity as asampled sequence ofquantized numeric values, typically but not necessarily in the form of a binary value. Digital sampling imposes somebandwidth anddynamic range constraints on the representation and addsquantization noise.
The termanalog signal usually refers toelectrical signals; however,mechanical,pneumatic,hydraulic, and other systems may also convey or be considered analog signals.
An analog signal uses some property of the medium to convey the signal's information. For example, ananeroid barometer uses rotary position as the signal to convey pressure information.[2] In an electrical signal, thevoltage,current, orfrequency 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 assound,light,temperature, position, orpressure. The physical variable is converted to an analog signal by atransducer. For example, sound striking the diaphragm of amicrophone induces corresponding fluctuations in the current produced by a coil in an electromagnetic microphone or the voltage produced by acondenser microphone. The voltage or the current is said to be ananalog of the sound.[citation needed][3]
An analog signal is subject toelectronic noise anddistortion introduced bycommunication channels,recording andsignal processing operations, which can progressively degrade thesignal-to-noise ratio (SNR). As the signal is transmitted, copied, or processed, the unavoidable noise introduced in the signal path will accumulate as ageneration loss, progressively and irreversibly degrading the SNR, until in extreme cases, the signal can be overwhelmed. Noise can show up ashiss andintermodulation distortion in audio signals, orsnow invideo signals. Generation loss is irreversible as there is no reliable method to distinguish the noise from the signal.[citation needed] Note that, despite a popular misconception, analog representations do not provide "infinite" resolution or accuracy, due to this inevitable presence of noise (and therefore error) in any real-world system.
^Horowitz and Hill, Paul and Winfield (24 April 2025).The Art of Electronics (3rd ed.). Cambridge, United Kingdom: Cambridge University Press (published 2015). p. 1225.ISBN978-0521809269.
Leach, W.M. (October 1994). "Fundamentals of low-noise analog circuit design".Proceedings of the IEEE.82 (10):1515–1538.doi:10.1109/5.326411.
Pawelczyk, M. (March 2009). "Analog Active Control of Acoustic Noise at a Virtual Location".IEEE Transactions on Control Systems Technology.17 (2):465–472.doi:10.1109/TCST.2008.2000988.
Muncy, Neil (1995). "Noise susceptibility in analog and digital signal processing systems".Journal of the Audio Engineering Society.43 (6):435–453.INIST3575490.
