Talk:Analog signal
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These three very similar articles need a proper merge and copyedit, but I haven't got time at the moment.
- Merged, but this now needs a thorough copyediting.
Sources: Some of an earlier version of this article was originally taken from Federal Standard 1037C in support of MIL-STD-188.
Now refactored a bit to flow better. Still needs more copyediting. -- The Anome 18:36, 29 Aug 2004 (UTC)
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[edit] Thoughts
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)
[edit] Link suggestions
An automated Wikipedia link suggester has some possible wiki link suggestions for the Analog article, and they have been placed on this page for your convenience.
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Do we want articles that aspire to sounding erudite? Articles that are comprehensive to the point of being chopped hash? These are the properties found in standard encyclopedias. We can be different by having plain, clear explanations.
[edit] Page move: Analog signal
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.
[edit] Support
- Cburnett 16:29, Jun 12, 2005 (UTC)
- James F. (talk) 20:26, 13 Jun 2005 (UTC)
- —Michael Z. 2005-06-17 04:47 Z
- taestell 01:32, Jun 19, 2005 (UTC)
- I've been doing link disambiguation for Analog, and the two topics are virtually identical. Nihiltres 22:44, 28 October 2006 (UTC)
[edit] Oppose
[edit] Other
[edit] Discussion
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)
[edit] False assertion?
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)
[edit] Correction
It was formerly asserted that a microphone's operating mechanism is a variance of current caused by sound pressure. This is technically incorrect (compare Microphone), since it is not current that varies with the sound pressure, but voltage. I've made this correction in the article. HarmonicSphere 03:03, 2 February 2006 (UTC)
...Unless you are talking about a carbon microphone—still found in older telephone sets—A carbon microphone effectively is a resistor whose value varies with sound pressure. When a carbon microphone is placed in a circuit that is supplied by a constant-voltage source (e.g., a battery), then the current in that circuit that will fluctuate in response to sound pressure fluctuations. Drondent 00:35, 18 July 2007 (UTC)
[edit] Added wikilinks
I made the anon changes, forgot to log in
[edit] Incorrect definition?
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)
- The introductory definition was very poor. It completely missed what an analogue signal really is. It suggested that any time continuous signal of constant amplitude is an analogue signal. But it isn't. To be analogue it has to be an analogue of some other quantity. I still don't think the definition is perfect (in that it isn't quite vague enough). I B Wright 10:21, 8 August 2007 (UTC)
[edit] Unrefenced Material
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)
