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To conform with digital signal and discrete signal (not digital (signal) and discrete (signal)). The fundamental difference between "analog signal" and "analog (signal)" is that the latter is a disambiguation of "analog" but "analog signal" is a perfectly acceptable usage.
Please put discussion here instead of in the voting section.
"Analog (signal)" swapped with "Analog signal" (preserve history of "Analog signal") after uncontested support of 4 to 0. Cburnett 05:02, Jun 19, 2005 (UTC)
Currently, the text claims that a digital may be distiguished from an analog signal by the meaningfulness of small fluctuations in the signal amplitude the latter and meaninglessness of them in the former. That doesn't sound right: I'm not aware of a natural law that says one can't make use of small differences in the signal amplitude in encoding and decoding digital data. Can anyone defend the current text's claim? Terry Oldberg 18:31, 15 December 2005 (UTC)
I think what's being referred to here is an effect called quantization, which limits the minimum possible capturable per cent difference between two volumes in a digital recording to the inverse of the number of bits in its sample resolution times 100. In a 16-bit audio recording, for instance, the minimum recordable difference in volume will be a 100/16, or 6.25, per cent difference in volume. The greater the sample resolution, the smaller the difference in volume can be recorded in a digital capture. This is an inherent physical limitation of digital recording, whereas in analog recording, which is produced by a continuous rather than a discrete process, this doesn't happen (although you get noise related to the medium — for example, line hum or tape hiss — creeping in).
A similar effect known as aliasing happens in the sampling rate: digital audio files cannot record a frequency higher than the Nyquist frequency, defined as half the sampling rate of the recording: e.g., a digital recording with a sampling rate of 44 KHz cannot record a frequency greater than 22 KHz.
Having said all this, the article's description is vague, almost to the point of inaccuracy. It should say that analog recording is a continuous wave function resulting from the impression of a fluctuation in the voltage of a current, caused by sound pressure, on a medium, whereas digital recording is a discrete (i.e. stepwise) series of snapshots of amplitude, with a maximum sampling frequency and sample resolution, and that these characteristics impose predictable limits on the maximum frequency and minimum difference in volume a digital recording can capture. HarmonicSphere 03:11, 2 February 2006 (UTC)
I don't have citations for these ideas, and I don't quite know how to work them into the relevant articles, but I'd like to throw them out there:
1) "Analog" and "Digital" describe two different kinds of computing machinery. The word, "analog" did not come into common use until after digital computers were invented.
2) "Signal Processing" machinery is computing machinery. A physical signal is a measurable quantity that contains information about some other quantity of interest, and signal processing machinery is machinery that transforms a signal in some useful way that typically can be described by a mathematical law.
3) "Analog" originally was a noun. An analog used to be a thing that somehow represented or stood for some other thing. When the "information" contained in a signal was simply the value of some other measured quantity, then it was acceptable to say, "the signal is an analog of the original quantity."
4) The word "electronic" describes electric circuits that process signals.
5) A "logical signal" can be imposed on a "physical signal" by means of modulation. In fact, there can be multiple levels of modulation. (e.g., subcarriers on a FM broadcast radio station.)
6) All "physical signals" are analog signals. All "digital signals" are logical signals.
7) "Noise" is the difference between the signal that you receive, and the signal that you wished to receive.
8) One reason for modulation is to provide immunity from noise. Digital signalling is often used for this purpose, but all-analog solutions can also provide significant noise immunity (e.g., FM broadcasting vs. AM broadcasting.)
Drondent 01:01, 18 July 2007 (UTC)
Although I haven't found any other (clear) definition of an analogue signal, I think the very first line of this article is not correct. Unless I'm very much mistaken, a signal is analogue as long as it is continuous in amplitude, and is not related to continuity in time. For instance, a Compact Cassette is considered an analogue medium. However, a compact cassette has a finite number of magnets, and is thus not continuous in time. Cassandra B 18:06, 22 April 2007 (UTC)
But we pretend that it is continuous. Any difference between the signal we expected to read off the tape and the signal that we actually read off of the tape is called "noise." If we want to analyze the noise, then it may be useful to know that part of it is due to the granularity of the medium. Drondent 00:30, 18 July 2007 (UTC)
Some kind Administrator has added an {{Unreferenced}} tag to the article. The subject matter of the article is such that any reasonably competant engineer could write such an article without reference to any other material. In practice such an article is likely to peer reviewed and edited by (hopefully) equally competant engineers, and as such, the article really doesn't require much in the way of references or citations. I B Wright 10:21, 8 August 2007 (UTC)
This article makes the false assertion that an analog signal has theoretically infinite resolution, then contrasts this with limitations of digital systems:
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.
First, the wording is imprecise. I think what is meant is "[...] it will always have a higher resolution than can be represented by a digital system [...]"
More importantly, the statement itself is a persistent myth that is the opposite to truth. Any analog signal will theoretically always have noise, and any analog transducer will have a finite response to changes in the signal. This places limitations on the resolution and bandwidth of analog systems. This is a consequence of the laws of physics and not just the imperfection of real-world implementation. Since any analog system will have a finite resolution and bandwidth, a digital system with a finite bit width and sampling rate can be built with the same fidelity as any analog system. There is therefore no point in specifically pointing out the limitations of digital systems.
63.81.178.62 (talk) 22:28, 17 July 2008 (UTC)
Just because a clock uses a digital signal at some point doesn't make it a "digital clock." All this does is confuse elementary school kids. What designates a clock as "digital" is changing digits, not a digital signal. See the English dictionary . This is in contrast to the dictionary definition of analog clock. Oicumayberight (talk) 06:03, 14 April 2009 (UTC)
I can't believe you are replacing sourced material with unsourced material. Oicumayberight (talk) 15:45, 14 April 2009 (UTC)
Reading the above and looking at the editing history, it seems to me that the whole issue turns on whether Oicumayberight accepts the concept of the analogue signal requirement of being continuous or not. Since I am an engineer in the Aerospace industry, I though I would draw an analogy from that industry, that illustrated the point. I was surprised to find that the analogy was turned on its head as will be revealed. Every reference book I checked made the point that the analog signal had to be continuous (It was even in my Uni notes). But to the analogy.
The Harrier aircraft uses mechanical wire linkages from the joystick to the control surfaces (elevator, ailerons & rudder). This is, of course unarguably an analogue signalling system. The wire linkage forms a continuous signal, and the control surfaces move in smooth continuous steps.
The Typhoon aircraft, in contrast, uses a digital system. The position of the pilot's joystick is digitised into a number which gets mashed around a bit by a computer. The resultant digital signal is then fed to the control surface via what is essentially a stepper hydraulic system. Both the signals and the movement of the control surfaces are described in all the manuals as digital, in spite of the bit size of the numbers being large enough that the movement may appear to be smooth to the pilot.
The surprise was that in the preamble notes (the part of the manual given to new starters as part of their training), the operation of the digital control contained an explanetary analogy where the system was likened to "... a clock with analogue hands where the movement of the hands is in fact discontinuous and hence, not really analogue at all."
In the subject context, the movement of the hands on a clock that has discontinuous movement (i.e. the majority of clocks) is not analogue and Oicumayberight is wrong to continue to insist that it is. I B Wright (talk) 18:13, 14 April 2009 (UTC)
I have sources for edits that are not circular. They are clear and concise definitions of what digital an analog mean as they pertain to clocks. But this doesn't even need to be in the article. The only source offered to support the claim that analog clocks are actually digital were circular references to www.wikianswers.com which cites this article as a source for defining analog and digital, and doesn't even mention clocks. I'm suggesting a compromise of removing the mention of clocks from this article altogether so that wikipedia is not adding to the confusion. Clocks are not the best examples to contrast the difference between analog and digital signals simply because of the widely accepted and well sourced alternate definitions of analog and digital as they pertain to clocks. Even IEEE agrees with those definitions. But they don't need to be in this article because they are about types of displays, not types of signals. Oicumayberight (talk) 00:47, 15 April 2009 (UTC)
I added the section "Display devices" because I realized that any display device (including clocks) are commonly referred to as "analog" or "digital" based on the final output which is visual information being displayed. Most pieces of electronic equipment deal with multiple signals. Those signals may vary from analog to digital within the same piece of equipment. It's a mistake to call the equipment analog or digital based on any one of those signals if the signal is merely another stage in the signal processing and not the final output. An analog television set may converts signals from analog to digital and then back to analog. I used electronic test equipment as an example in this section because it's all about displaying signals with minimal conversion or modulation.
I went back on my suggestion to compromise by not mentioning clocks and used them as an example in this section just to show a wider variety of examples than electronic test equipment and because clocks are a more common example. If someone feels strongly that the clock examples hurt more than they help understanding, feel free to remove them. However, I think it would be a mistake not to show at least one example of display equipment in which a signal is converted from digital to analog or analog to digital. Anyone familiar with electronic signal processing should also be familiar with electronic test equipment. The important thing to know is that signal types aren't necessary the same thing as display types. Oicumayberight (talk) 16:23, 20 April 2009 (UTC)
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