Talk:Signal/Archive 1

Archive 1

Correction

Under Analog and Digital Signals -> Discretization, it says,

"DT signals often arise via of CT signals."

Should this just say, "via"?

--208.188.2.93 18:20, 18 July 2006 (UTC)

Yes, fix it. Dicklyon 18:34, 18 July 2006 (UTC)

Old talk

As I understand it, a signal needs a temporal component (modulation in time). But the Fourier transform of that signal loses the temporal component. Thus I do not see how that FT(signal) can also be called a signal, which is why I renamed it signature, which describes a characteristic of said signal. Ancheta Wis 02:01, 27 Feb 2004 (UTC)

An FT of a signal is much more than a signature: It contains all of the same information as the original signal---very different from the idea of, for example, a Digital Signature. 71.253.0.236 03:45, 25 July 2007 (UTC)

On Nov. 30, 2005, I edited the article extensively, to correct the following problems: a) mistatement of the notion of a signal in information theory-the notion is not that it is a flow of information but rather that it is a sequence of states of a communications channel at the transmitter. b) confusion of "data" with "signal"- Some of the problems are: a) analog and digital are properties of data NOT signals. b) it is possible to perform frequency analysis on data but is not possible to perform it on a signal c) a signal is not a sequence of numbers but a sequence of numbers can be properly referenced as "data." As the article is about "signal" and not about "data," the best way to handle this situation seems to be to edit out the references to "signals" that are really "data." c) The claim that entropy is a property of a signal or set of signals is incorrect. Entropy is a property of a communications channel. As the article is about the concept of a "signal," it seems best to leave out discussion of entropy.

One of the properties of the "signal" that is defined in information theory is that the process that generates it it is a stochastic process. As this is sometimes a source of confusion, I added a discussion of this topic. Terry Oldberg http://www.oldberg.biz terry@oldberg.biz

Hours after I contributed an edit or the article plus the above justification for it, "Shanel" wiped it out without supplying a justification. Shanel: please either attempt a justification of your action or restore the text as edited by me.

Terry Oldberg Dec. 1, 2005

---

Terry, what other characteristics of signals ar there besides the stochastic attribute of the signal-generating process? And why is that one so important? What about the channel's characteristics and influence? Your first paragraph is useful because it helps people distinguish a signal from a waveform and a message. Many people have the concept of a signal as something radiating from the tip of an antennae, i.e. radar and radio and many people would probably relate to that. Many people discover signals through their interest in digital audio/video. People coming from different backgrounds should find something they can relate to in the article. Rtdrury 20:56, 3 December 2005 (UTC)

RTdrury: The stochastic attribute is important because it implies a constraint on the signal-generating process, for not all processes are stochastic. I'm sensitive to this problem as a result of having once attempted statistical research in the field of nondestructive testing. Through misuse of the word "signal," workers in the field implied that a process was stochastic when it was not. In doing so, they implied that this process obeyed conventional statistics when this was not true. One of the results of the misuse was (and still is) to expose the people of the world to unnecessary hazards from such events as explosions of nuclear reactors and downings of aircraft. You are quite right in implying that the channel characteristics and influence are important. However, it seems to me that it would help untangle Wikipedia if they were to be discussed in a separate article on the notion of a communications channel. After all, a signal and a communications channel are two, different entities.

Terry Oldberg 07:25, 15 December 2005 (UTC)

I came onto this article looking for a place to Wiki-link the term signal in the article Optical communications. The old article seems to have roughly the definition of signal that is used in that field, that is, a time-varying quantity of interest, regardless of how it was produced. But, as Terry points out, thats not the correct definition for the field of information theory. I'd like to move the old article to a new title like "signal (circuit theory)" or "signal (circuits and systems)" or "signal (communications)", but I'm not sure of the best title --- anyone feeling a little more bold want to just pick? -- The Photon 01:54, 4 December 2005 (UTC)

I'm not clear on the distinction you draw between signals and data. For instance, I gather that you're trying to distinguish a digital data stream from the continuous electrical quantities that represent it, but it would be good if you could explain what exactly you mean. Furthermore, as the author of this article, I have to say that everything I've been taught in two semesters of signals theory supports the definitions I used.

Finally, as far as wiki etiquette is concerned, if you ever see the need to delete a large amount of text from an article, please replace it somewhere else. For now, I'm going to put the text that you've removed back into the article, with a note saying that you contest its accuracy. --Smack (talk) 03:40, 14 December 2005 (UTC)

Smack, are you certain that the definition of "signal" is the same in information theory and in signals theory? I don't know if signals theory is the same as what we called "signal analysis" in my university, but if it is, that field uses very different tools from information theory, and I'm not surprised if information theory has a very specific definition of "signal", and its not what you'd expect if you aren't an information theory (since very little in information theory is what you'd expect from lay knowledge of the terms they use). Again let me suggest moving the current article to Signal analysis or Signal (circuits and systems), and let the information theory people have an article that correctly relates to information theory.

The Photon 05:11, 14 December 2005 (UTC)

Smack: That there is controversy on the wording of the article asks whether there is an important distinction between a number and the representation of a number in telecommunications hardware; the latter is a sequence of states of the communications channel. If this distinction is preserved, there is, for example, a difference between 01100011 and the sequence of states of a communications channel that represents this number during transmission. The former is a sequence of digits. The latter may sequence of voltages across conductors. Should we blur the distinction between the former and the latter?

In the defining paper of information theory, "A Mathematical Theory of Communications," Shannon distinguishes between the two. Numbers are a subset of the "characters" which, in sequence, make up what Shannon calls a "message." The sequence of states of the communications channel, at the transmitter end of it, make up what Shannon calls the "signal." Shannon's "message" is what one now calls the "data."

Shannon's "received signal" differs from his "signal" through the entry into the communications channel of noise but the received message may, through the use of an error correcting code, be identical to the transmitted message. His "signal" may be continuous in time when his "message" is discrete in time, or vice versa. These are some of the differences between Shannon's "signal" and his "message."

In view of the above facts, I submit that it is essential for Wikipedia's article on "signal (information theory)" to preserve the distinction between a number and the representation of a number as a sequence of states of a physical system. When this distinction is preserved, a "signal" is a sequence of states, at the transmitter. A number or sequence of numbers is a subset of what Shannon calls a "message" and one now calls "data." The "signal" encodes the "message."

Terry Oldberg 07:25, 15 December 2005 (UTC)

Terry, You inspired me to look up Shannon's paper (here). Shannon does mention both messages and signals which occur in discrete time, and he mentions both continuously valued and quantized signals as well (his example is a telegram, where the signal is composed of "dots, dashses, and spaces"). This seems to make much of the discussion about digital and analog signals as well as discrete-time and continuous-time signals relevant to information theory. Is there a different preferred terminology in information theory that you could put in place of "analog", "discrete", etc., instead of removing these sections entirely?

Part I of Shannon's paper is titled "the discrete noiseless system", in which the transmitter, channel, and receiver are all noise-free. The bulk of Part I is a discussion of the statistical nature of the message: "the messages to be transmitted consist of sequences of letters...they form sentences and have the statistical structure of, say, English." It looks as if Shannon's formulation calls for the message to be generated by a stochasitic process (or a process which, since we can't predict it, we must model as a stochastic process). For example, he generates a number of articifial sentences, with increasingly sophisticated models of English. Sections 2, 3, 4, 5, 6, and 7 of Part I discuss the stochastic nature of the source of the message. The transmitted signal has a stochastic nature only because it is generated (noiselessly) from the stochastic message.

Shannon's Theorem 7 relates the entropy of the transmitted signal to the entropy of the source, or of the message. That Shannon would calculate the entropy of a signal seems to conflict with the statement that "The claim that entropy is a property of a signal or set of signals is incorrect." Shannon's paper refers to the entropy of both message sources and signals, and the capacity of the channel.

In Part II Shannon uses the term received signal, indicating that the term signal is not only associated with the output of the transmitter and the input to the channel. This seems to conflict with the definition of a signal as "the sequence of states of a communications channel that encodes a message, at the transmitter end of the channel" [emphasis added].

I'm not yet clear on whether frequency analysis has a place here. I hadn't yet dug it out of Shannon's paper, but I've just noticed in Part III there is some discussion of channels characterized by their frequency and impulse response --- I'll withold any opinion until I've dug in further to that part of the paper.

To wrap up, going by Shannon's paper, most of the current version of the article does seem to be relevant to information theory. Signals may be either discrete-time or continuous, and they may be either continuously valued or quantized, but perhaps information theory uses different words for these concepts. Signals may occur at either end of a channel, and they are characterized by an associated entropy. There is still some room for improvement in the article to clarify the difference between sources, messages, signals, and channels; and the terminology might not be exactly right for information theory. Nonetheless the bulk of the material in the article should be cleaned up, not eliminated.

The Photon 07:03, 16 December 2005 (UTC)

It looks like this is the time for me to step aside from this issue. What's the difference between information theory and signals theory? I wanted to name this article "Signal (signals theory)", but that would have been a circular definition. I also don't like the proposed qualifier "circuits and systems", because signal theory transcends electrical engineering. --Smack (talk) 19:45, 21 December 2005 (UTC)

Have a look at these questions in their most primitive form: a single bit of information is represented by a change in state, from one thing to another thing. So to measure anything, you need always to compare two things (before+after, upper/lower bound, hotter/colder etfc.). This change may be discrete or continuous, and is called a signal. -- Waveguy 22:37, 21 December 2005 (UTC)

Recommend the Usage of Standard Signal and System Text

Regarding the comment from 2004 at the top of this page, in ABET accredited ELE/ECE junior-level signal and systems courses, a periodic time-domain signal is defined as a type of vector. Its vector components can be determined by way of the fourier series. The notion of a vector carries over into non-periodic signals where the fourier series is generalized to the fourier transform. A highly respectable reference to this train of thought can be found in Signal Processing and Linear Systems by B.P. Lathi. I suggest the addition of these and similar structural ideas from B.P. Lathi's text or another standard ELE/ECE text such as Continous and Discrete Signal and System Analysis by George R. Cooper and Clare D. McGillem. --Firefly322 03:33, 22 June 2007 (UTC)

Certainly describing signals as vectors can be worthwhile. Limiting to signals that are periodic, or that have Fourier transforms, however, is pretty limiting, as it leaves out for example the signals that are stationary random processes. And lots of decompositions besides Fourier ones are important. So if you go there, try not to make it too narrowing. Dicklyon 03:41, 22 June 2007 (UTC)

I do also agree that relying on a good solid source like a text book would lead to improvements. And if I don't like what your book says, I'll be motivated to go find alternatives in other books. Too often we argue here just because we're too lazy to find sources. Dicklyon 03:45, 22 June 2007 (UTC)

Okay, thanks for the fast feedback... Now I realize it's not often taught in this way, but a process, random or otherwise, is in fact just a sequence of events. A good example is a Markov Chain where each probability matrix in the chain can be viewed as a single hyper-number conceptually similar to other hyper-numbers (e.g., a quaternion or an octonion). Anyway, my ultimate perspective is that random processes have components that map to the elements of vectors/matrixes just as any signal will--periodic or otherwise. And I'm just wondering if you are suggesting something else? --Firefly322 03:59, 22 June 2007 (UTC)

Just pointing out that if you define signals in Fourier space, i.e. as Fourier series or Fourier transforms, then you leave out the ability to represent all the non-periodic non-square-integrable signals such as noise processes, etc. And I was thiking of continuous-time processes, finite-order or otherwise, but you're right that discrete-time processes are also in need of good representations.

Certainly, transformations and decompositions can and should be extended to Laplace and beyond. Keep in mind that all real-world signals can be transformed by either Fourier Transform or the Fourier series. Even PIE-IN-THE-SKY ideal-signals such as those of non-periodic infinite energy (i.e., your non-square integrable example) can be transformed with a little care (e.g. take into account the range of interest, etc). --Firefly322 05:17, 22 June 2007 (UTC)

Generally, that's where I disagree. "A little care" means you need to change to some other technique, such as spectral density via Wiener–Khinchin theorem, in which case you don't have a basis but only a second-order statistic, or short-time techniques; that's why you need to be careful about using Fourier techniques in a definition of signals. Dicklyon 17:44, 1 July 2007 (UTC)

Moreover, that's where I disagree. Signals are a part of nature. And nature can never be designed out. Hence I've seen neither a Signals and Systems nor a Controls problem where certain didactic ideas such as you now mention have truly proven themselves. My belief is the Wiener-Kinchin theorem is in fact neither necessary nor useful. And if truth be told it has proven itself a weak didactic idea that should no longer be given much notice even inside a graduate school curriculum. Firefly322 14:52, 18 July 2007 (UTC)

There are many, many important results stemming from random signal theory which cannot be derived in any other way. Some examples off the top of my head are Wiener filters, Kalman filters (many applications in both signal processing and control), the ARMA model and its applications (e.g., linear predictive coding, which is used in voice compression). These are all based on the idea of a spectral density and of modeling a signal as a random process. How can you say that these ideas haven't "proven themselves"? --Zvika 14:45, 18 July 2007 (UTC)

At best these ideas are intellectual puffery, at worst they represent a case of the emperor having no clothes. I see it as specious to hold random signal theory so important. These applications can be and were derived from basic signal and systems and control theories. Firefly322 14:56, 18 July 2007 (UTC) (UTC)

I suggest you refrain from name-calling, as it will not advance the discussion. Are you saying that the Kalman filter, for example, can be derived without using random signal theory? Can you cite a verifiable source to that effect? If so, that would certainly be an interesting addition to the Kalman filter article (and to my own knowledge of the subject). --Zvika 15:28, 18 July 2007 (UTC)

It sounds as if I am being warned not to commit a thoughtcrime. So exactly what does Zvika mean by name-calling? Just to be pre-emptive, are you anything at all like Betrand Russell? He lied to the Western World about what he had seen firsthand in the Soviet Union. That's a historical fact. And this is relevant. Wiener studied with Russell for a time. Both Wiener and Russell's work were, if not designed (though that is highly debateable), at least used by their authors in furthering their socialistic/communistic political agendas. [Well documented historical facts that have numerous sources] So anyway forgive me if I'm wrong, but more often than not, when professors or whoever bring up Wiener they are conciously or subconciously bringing up a hidden agenda. Firefly322 03:40, 22 July 2007 (UTC)

History records that a tracking/prediction system of Black et al from Bell Telephone Laboratories went head to head with one designed to Wiener's theories. The BTL system performed far better than the one designed according to Weiner's theories. [A history of control engineering, 1930-1955 / S. Bennett, 1993; IEE control engineering series ; v. 47 ] Firefly322 17:57, 21 July 2007 (UTC)

If history records that, find the source and write it up in the wikipedia. I'd be very interested. And it would give you a more constructive way to contribute than just knocking what others have contributed. Dicklyon 20:22, 21 July 2007 (UTC)

"knocking what others have contributed..." Thanks if you're implying that I have made no contributions. My first comment on this page was due to some foolish errors about the meaning of signals that were easily dispelled through standard references. Now that I have in fact contributed a source as requested by Zvika, the next step would be for him to read it and share thoughts. Firefly322 03:46, 22 July 2007 (UTC)

Right, as far as I can see, you've editted nothing but this talk page, and have said nothing constructive yet. Also, please learn to use the preview feature so that you don't have to make dozens of edits to add one comment. Dicklyon 05:57, 22 July 2007 (UTC)

I would also recommend reading "A New Approach to Linear Filtering and Prediction Problems" by R.E. Kalman, Transactions of the ASME, Journal of Basic Engineering March 1960 p.35-44. and "New Results in Linear Filtering and Prediction Theory" by R.E. Kalman and R.S.Bucy, Transactions of the ASME, Journal of Basic Engineering March 1961 95-104 There is very limited evidence as to whether these papers have made actual contributions to engineering itself as represented in actual designs. References by other papers and professors I find very weak, especially in light of the public political agendas of such "contributors" as Wiener and Russell. Firefly322 04:09, 22 July 2007 (UTC)

Indeed, it has been a long time since I've read those; good idea to read again. But what is the political agenda that you're referring to? And where can I read about that? Dicklyon 05:57, 22 July 2007 (UTC)

1950. The Human Use of Human Beings by Norbert Wiener.

1966. God & Golem, Inc.: A Comment on Certain Points Where Cybernetics Impinges on Religion by Norbert Wiener.

Firefly322 06:46, 22 July 2007 (UTC)

OK, I got the books, and read parts of them. Seems like he was trying to be thoughtful and philosophical about how his contributions to "cybernetics" would interact with society. If it's political, it's not very good politics, because I pretty don't get what his agenda is. But in any case, I don't see how these writings dilute in any way the validity of his mathematical contributions to random signal theory and such. Dicklyon 07:02, 5 August 2007 (UTC)

Seriously, I have had enough of this conversation. You wanna contribute something to Wikipedia, go ahead and do it. That's the whole point of Wikipedia: if you think can correct something, you can go ahead and do it. --Zvika 08:28, 22 July 2007 (UTC)

Done. Just added a moderately reasonable introduction. Firefly322 17:07, 17 December 2007 (UTC)

Signal Propagation

I know this might be obvious to you geniuses out there, but I was really hoping to find out the mechanism by which a voltage signal propagates through a wire, how fast the propagation occurs (speed of light?) what is the physical carrier of the signal, etc. (I know electrons, but does it involve electromagnetism as in a radio or light waves, or is it just fluctuations in the voltage (electron density) and if voltage only, given the fact that electrons have mass, how does the wave propagate so fast?) Lenehey (talk) 19:36, 30 April 2009 (UTC)

It depends, but is not at all obvious; but always at least somewhat slower than the speed of light. See Telegrapher's equations and Oliver Heaviside. Dicklyon (talk) 22:34, 30 April 2009 (UTC)

The reason I say "it depends" is that there are two very important distinct regimes: resistance-dominated wires, where the charge flows by diffusion, versus the ones where signals propagate primarily as guided waves. What kind of wires are you concerned about? Dicklyon (talk) 22:40, 30 April 2009 (UTC)

Need a broader definition of Signal

The current message-oriented definition is way too narrow. Articles such as Spectral density need to reference signal, but there's no appropriate definition. Should we make yet another signal page for the broader definition? Or just broaden this one?

At the risk of opening up a can of worms, I'm going to attempt a new broad intro. Dicklyon 01:58, 3 June 2006 (UTC)

I agree with you. Also, I think the title should be "Signal (electrical engineering)". I think there is no need to have a separate article for "Signal (information theory)" (we can have as a small section of this article). BorzouBarzegar 17:59, 7 June 2006 (UTC)

I agree it would be nice to have something to link to the word signal, but on the other hand Wikipedia is not a dictionary. Despite all the fuss I went to above over this article, I now think the real best answer is to define the term signal in the appropriate articles, such as Information theory, Telecommunications, Signal processing, etc. This article is either just a dictionary definition, or a second-rate rehash of what ought to be in those other articles.

That said, if you're going to keep this article, but broaden its sense to cover meanings of the word signal outside of information theory, then the name should definitely be changed. -- The Photon 04:40, 8 June 2006 (UTC)

The concept of Signal in Electrical Engineering definitely needs an article. BorzouBarzegar 15:56, 8 June 2006 (UTC)

If you mean we need distinct pages, what definitions would you use that would be different between information theory and electrical engineering. In all my training, I never found such a distinction. Or are you just supporting renaming this one? Dicklyon 17:44, 8 June 2006 (UTC)

I'm just supporting renaming this one to "Signal (electrical engineering)". BorzouBarzegar 19:57, 8 June 2006 (UTC)

It seems that there isn't any objection to change the title. So, I move the page. BorzouBarzegar 20:32, 8 June 2006 (UTC)

I think it should be moved back to Signal (information theory), or maybe something else entirely. As the "examples" section of the page points out, "signal" is something that is used by biology, physics, etc. A continuous signal can be sent from point A to point B without an electrical circuit ever being involved. Neurons are the clearest example, but I'm sure there are (and will be) other examples. --Interiot 20:09, 21 May 2007 (UTC)

That's true, but electrical engineering is the field in which signals are mostly studied, so it works as it is. Information theory talks about signals, but has a rather narrower view of them than is used in EE and other fields, where they are quite often treated outside of an information framework. Dicklyon 03:02, 22 May 2007 (UTC)

Definitely should be moved back. I had to mv Signal (biology) because for example in ethology (a sub-field of biology) a "signal" is not a single neuronal impulse, but just what is described here (a la "Within a complex society, any set of human information...", replacing "a complex society" with "intelligent species" and "human" with "animal"). See de:Signal#Nicht technische Signale for what is missing from en: almost entirely. Social signals are just a non-technical equivalent to the "signals" discussed here. Dysmorodrepanis (talk) 00:44, 10 September 2009 (UTC)

I consulted Wikipedia because I need an authoritative (abstract) definition for a publication. And I found no answer. IMHO "signals" should be abstracted from electronics. And a signal is definitely not just a quantity varying in time. The temperature in this room is varying, but is not a signal. In my perception, a signal is coded information in a communication process. Isn't all information coded? No, information at an abstract level (knowledge in my head) is a conception independent of the neurons in my brain. Isn't all information used for communication? No, the essence of communication is that it is an act that needs a device. It is inevitably imperfect. Which leads to the idea that signals are the opposite of noise. What is noise? Is it meaningless information, like a random sequence of letters? Or is meaningless information a contradictio in terminis, and is noise just a varying quantity without meaning? But I would not call the (varying) temperature in this room "noise". Rbakels (talk) 06:01, 10 April 2012 (UTC)

Why would you consult Wikipedia if you want an authoritative result? Wikipedia is not a source. Dicklyon (talk) 06:59, 10 April 2012 (UTC)

"Electrical" or "electronic"

Also, why not "electrical" instead of "electronic"? Such signals were used in telephony and telegraphy long before we had electronics. See [1]. Dicklyon (talk) 18:25, 11 April 2012 (UTC)

My acquaintance with these two terms is that "electronic" refers directly to stuff involving components, like transistors or tubes, while electrical refers to anything to do with electricity, especially in its old-fashioned sense. My guess is that an electronic signal tends to be one associated with electronics, while an electrical signal doesn't emphasize the signal processing aspects so much as the distinction between electric signals, smoke signals, and football signals. Brews ohare (talk) 20:10, 11 April 2012 (UTC)

I think it would be better to change the title back, and add a section on specialization to electrical/electronic signals. Dicklyon (talk) 18:31, 11 April 2012 (UTC)

Introduction not specific

The topic for this article is electronic signals, not the general topic of signal. Perhaps the individual topics on the disambiguation page require a general article to interrelate the various aspects, but that is not the role of this article.

The present introduction is much too broad in scope for this narrow subject, and doesn't get directly to the point of electronic signals. Instead it attempts to provide the most general context possible, which, if it is needed in this article at all, should be a subsidiary topic like "Context". Brews ohare (talk) 15:06, 11 April 2012 (UTC)

I think the problem is more the title than the content. Consider moving it back to Signal (electrical engineering), from whence it was moved in 2008, and see if it makes more sense that way. Dicklyon (talk) 15:16, 11 April 2012 (UTC)

The following removed introduction seems to me to fit the topic Signal (electronics). If I understand your remarks, Dick, the present article should be moved to another topic, and a new article written for Signal (electronics)?

Signal transmission using electronic signals

An electronic signal is the embodiment of a signal in electrical form made by a transducer that converts the signal from whatever its original form to a waveform expressed as a voltage or a current, or an electromagnetic waveform, for example, an optical signal. Once expressed as an electronic signal, the signal is available for further processing by electrical devices such as electronic amplifiers and electronic filters, and can be transmitted to a remote location by electronic transmitters and received using electronic receivers.

Brews ohare (talk) 16:57, 11 April 2012 (UTC)

Not another topic, but maybe another title. Whether there is also room for a separate more specific topic on electronic signals is a separate question; I'm just saying there's not reason to make this article's topic so narrow, just because of its title. Dicklyon (talk) 18:18, 11 April 2012 (UTC)

I inserted this material as a separate sub-topic Signal processing, with a link to Signal processing. IMO it is an essential point to show how signals in general are analyzed and processed following their translation into electrical form. Without this background, most of the context for electronic signals is lost. Brews ohare (talk) 16:13, 12 April 2012 (UTC)

Proposed changes

I'd suggest restoring Signal to Signal (disambiguation) and making Signal a page containing the present article but omitting the section on digital and analog signals. Then Signal (electronics) can incorporate the introduction proposed above and this section. Brews ohare (talk) 17:21, 11 April 2012 (UTC)

You'd have to do a multi-WP:RM and argue that this topic is WP:PRIMARYTOPIC for Signal. Given the number of ambiguous items there, I doubt you'd get much support for that. Dicklyon (talk) 18:18, 11 April 2012 (UTC)

It looks like Signal (electronics) already is adopted as a primary topic for signal by virtue of the title of the present article Signal (electronics). I'd argue that at the moment, however, Signal (electronics) is devoted primarily to the topic Signal and not so much to the topic Signal (electronics).

For example, the introduction begins with

"A signal is any stream of quantities in time or spatial sequence. Signals categorizes to the fields of communications, signal processing, and to electrical engineering more generally."

and goes on to say:

"In the physical world, any quantity measurable through time or over space can be taken as a signal. Within a complex society, any set of human information or machine data can also be taken as a signal. Such information or machine data (for example, the dots on a screen, the ink making up text on a paper page, or the words now flowing into the reader's mind) must all be part of systems existing in the physical world – either living or non-living."

None of this is directed at the specific subject Signal (electronics), but does apply to the topic Signal, if that were released from being a proxy for Signal (disambiguation). Brews ohare (talk) 20:20, 11 April 2012 (UTC)

You don't seem to understand disambiguation and WP:PRIMARYTOPIC. There's no chance that you'll win a proposal to make this article primary for Signal, because there are so many alternatives listed at Signal, and this topic doesn't swamp the sum of all the others in popularity and importance. The disambiguators that have been tried here, (electrical engineering), (electronics), and (information theory), are attempts to say what kind of signal the article is about, not to limit it more narrowly than what you're thinking of as "Signal". The titling is imperfect, but that's life in WP. Dicklyon (talk) 20:54, 11 April 2012 (UTC)

It's not going to happen. 'Signal' has all sorts of meanings, many of which are more common to the average reader than this. But mostly it's a common word which is used in all sorts of ways so as a page is naturally a disambiguation page.--JohnBlackburne^words_deeds 21:11, 11 April 2012 (UTC)

Well, you all, WP is a weird place to be sure. But it seemed to me that a disambiguation page was designed to list all the various topics a word like "signal" might mean and link to the appropriate topics. So why is it that instead of Signal (disambiguation) serving that purpose, it is Signal being used that way? The article Signal could be used to provide general guidance, which is exactly what the material from the intro attempts:

"A signal is any stream of quantities in time or spatial sequence. Signals categorizes to the fields of communications, signal processing, and to electrical engineering more generally."

and goes on to say:

"In the physical world, any quantity measurable through time or over space can be taken as a signal. Within a complex society, any set of human information or machine data can also be taken as a signal. Such information or machine data (for example, the dots on a screen, the ink making up text on a paper page, or the words now flowing into the reader's mind) must all be part of systems existing in the physical world – either living or non-living."

Whatever is done about this matter, it remains obvious that the article Signal (electronics) as it presently exists is misapplied to serve as purveyor of generalities and doesn't address the topic of electronic signalling.

Brews ohare (talk) 22:21, 11 April 2012 (UTC)

As already linked, WP:PRIMARYTOPIC is the relevant topic. The relevant criteria is

1. A topic is primary for a term, with respect to usage, if it is highly likely—much more likely than any other topic, and more likely than all the other topics combined—to be the topic sought when a reader searches for that term.

And as already noted for most readers who are not interested in electronics other uses are far more prevalent. Or see wikt:signal which doesn't even mention electronics.--JohnBlackburne^words_deeds 23:00, 11 April 2012 (UTC)

Yes, "WP is a weird place". But it has a certain logic once you get to know it. When a user enters "Signal", it goes to the disambiguation page, Signal, becuase there is no PRIMARY topic for Signal. If there was a PRIMARY topic, then Signal would go there, and the disambiguation page would be at Signal (disambiguation). Call it weird, but that's what it is. And as for your complaint that "it remains obvious that the article Signal (electronics) as it presently exists is misapplied to serve as purveyor of generalities and doesn't address the topic of electronic signalling", as I explained, the problem isn't anything about the article, which is about signals as the term is understood in EE; the problem is just that the disambiguator (electronics) is not ideal. Why don't you fix it by doing a WP:RM to Signal (electrical engineering) or some better title of your choice? But you can't choose Signal, because that's taken, as a disambig page. Dicklyon (talk) 23:07, 11 April 2012 (UTC)

Dick, Idée fixe is a disambiguation page; Centrifugal force is not a disambiguation page, but a synopsis of various other article on Centrifugal force, Coriolis effect is an article on one meaning and refers to Coriolis effect (perception) for another. So I guess I'll have to figure out how all this works for Signal. It seems that there are too many forms for Signal to do other than what has been done already. So a page like Signal (common meanings) might be needed? Brews ohare (talk) 05:14, 12 April 2012 (UTC)

Regarding your diagnosis:

"as I explained, the problem isn't anything about the article, which is about signals as the term is understood in EE; the problem is just that the disambiguator (electronics) is not ideal",

Dick, I do not see that the discussion in the intro is about the term "signal" as applied in EE. Rather it is about signal in everyday common usage that applies equally to smoke signals. I am talking about this text:

"A signal is any stream of quantities in time or spatial sequence. Signals categorizes to the fields of communications, signal processing, and to electrical engineering more generally."

and goes on to say:

"In the physical world, any quantity measurable through time or over space can be taken as a signal. Within a complex society, any set of human information or machine data can also be taken as a signal. Such information or machine data (for example, the dots on a screen, the ink making up text on a paper page, or the words now flowing into the reader's mind) must all be part of systems existing in the physical world – either living or non-living." Brews ohare (talk) 11:51, 12 April 2012 (UTC)

Likewise, the subsection Examples of signals is only tangentially related to electronic signals. Brews ohare (talk) 16:35, 12 April 2012 (UTC)

Draft page proposal for generalities

A dummy draft Signal (communications) page that moves the generalities of Signal (electronics) to a more appropriate venue is proposed. The suggestion is that the material in this draft (which material all is taken from the existing article Signal (electronics)) be removed from Signal (electronics) to this new venue, allowing Signal (electronics) to focus directly on the electronic forms of signals. Comments are invited. Brews ohare (talk) 13:42, 13 April 2012 (UTC)

Comments

*Comment

Much of Signal (electronics) is about signals in everyday common usage and applies as much to smoke signals as to signals in electronics. This proposed new article would move only these generalities to a broader context, and free up Signal (electronics) to devote itself to its actual, narrower subject, particularly in its introductory section. Brews ohare (talk) 13:42, 13 April 2012 (UTC)

This division also opens the way to a clearer development of both the general and the specific topic, which no longer will be mixed together. Brews ohare (talk) 14:51, 13 April 2012 (UTC)

*Comment

The current scope seems compatible with what the IEEE Signal Processing Society says they do. It's not clear what benefit you envision from splitting it up. Dicklyon (talk) 15:14, 13 April 2012 (UTC)

Dick, there is no point in using an article devoted to signals that are electrical waveforms expressed as voltage, currents or EM waves, to include material that applies to smoke signals and traffic lights. By focusing on these topics separately, a clearer presentation is possible.

IEEE Signal Processing Society says their "field of interest" is signal processing, not signals, as their name implies. For their purposes:

"The term "signal" includes, among others, audio, video, speech, image, communication, geophysical, sonar, radar, medical and musical signals. Examples of topics of interest include, but are not limited to, information processing and the theory and application of filtering, coding, transmitting, estimating, detecting, analyzing, recognizing, synthesizing, recording, and reproducing signals."

This statement seems to indicate quite clearly that this organization is not restricted to Signal (electronics), but deals with Signal (communications), and points out the need for such an article with broader scope. Brews ohare (talk) 15:28, 13 April 2012 (UTC)

So a move of the present article to Signal (electrical engineering) would solve the problem? Dicklyon (talk) 15:34, 13 April 2012 (UTC)

No. See below. Brews ohare (talk) 15:54, 13 April 2012 (UTC)

*Comment

Transferring this article from Signal (electronics) to Signal (electrical engineering) does broaden the topic to include a broader subject area. To gain some idea of this range, the IEEE applies the term as: "the term "signal" includes, among others, audio, video, speech, image, communication, geophysical, sonar, radar, medical and musical signals." However, the term "signal" itself is not defined.

The article Signal (electrical engineering), however, does attempt to define the term "signal" as applied in EE. The article says:

"In the physical world, any quantity measurable through time or over space can be taken as a signal. Within a complex society, any set of human information or machine data can also be taken as a signal. Such information or machine data (for example, the dots on a screen, the ink making up text on a paper page, or the words now flowing into the reader's mind) must all be part of systems existing in the physical world – either living or non-living."

Although factually incorrect, because a time-varying quantity is necessary in order that a message or information be conveyed, and the variation need not be measurable in a quantitative sense to convey a message but merely discernible, this paragraph attempts to cover every conceivable meaning of signal, including turn signals, flag signals, and Extrasensory perception. It attempts to go way beyond the realm of EE.

Likewise, the subsection Examples of signals is only tangentially related to signals as dealt with within EE.

So, transfer of this article to a new name has not fixed its drawbacks, and the proposed new article is a better response to the problem of defining "signal' generally, and leaving Signal (electronics) to cover the normally understood topic:

"In electronics, a signal is an electric current or electromagnetic field used to convey data from one place to another. The simplest form of signal is a direct current (DC) that is switched on and off; this is the principle by which the early telegraph worked. More complex signals consist of an alternating-current (AC) or electromagnetic carrier that contains one or more data streams." Brews ohare (talk) 23:02, 13 April 2012 (UTC)

Moved back to Signal (electrical engineering)

The 2008 move to Signal (electronics) was undiscussed (there's not a single talk page comment that year) and is causing problems (see discussions above) due to its too-narrow scope relative to the article's topic. So I moved it back to solve the problem. If anyone objects, let's talk about other ways to deal with the problem. Dicklyon (talk) 15:41, 13 April 2012 (UTC)

Dick: The subject Signal (electrical engineering) still is too narrow to cover "audio, video, speech, image, communication, geophysical, sonar, radar, medical and musical signals", not to mention smoke signals, psychological signals, animal signals and traffic lights. In addition, if Signal (electrical engineering) is to be interpreted (incorrectly, I'd say) as a catch-all, there is now no article narrowly devoted to signals expressed as waveforms of voltage, current, or electromagnetic waves.

So the RfC still is worth pursuing. Brews ohare (talk) 16:00, 13 April 2012 (UTC)

Perhaps you might take a look at the proposed page to see what it contains? That might change your perception of what is involved here. Brews ohare (talk) 16:04, 13 April 2012 (UTC)

This is a much better name, yes: such signals are electrical in nature, not electronic. The electronics of such should be covered elsewhere such as in articles on radio, television, or on particular aspects of electronics.

As for other forms of signals I'm sure other articles cover them, though I can't be bothered to search. Some such as smoke signals I'm sure exist, while others such as audio signals may be covered under different topics (ah, that one works and isn't a redirect). So there's no need for a broad article on all sorts of signals. There seems too much general content in this article which should be pared back to narrow the focus of this article.--JohnBlackburne^words_deeds 16:49, 13 April 2012 (UTC)

John, forgive me, but I am unsure of your meaning. Let me see if I've got it:

1. You do not think the material in Signal (communications) is useful as a separate article, and Wikipedia does not need to discuss this term in a general context.
2. You do think that the general material in Signal (communications) belongs in Signal (electrical engineering), and you are aware that this information presently is there. The fact that this information is very broad in scope and could be included equally well in all the other articles on signals, like audio signals and smoke signals, is not a problem.
3. You do not think that a specialized article Signal (electronics) on the topic of electronic signals specifically in the form of electrical current, voltage, or electromagnetic waveforms is worthwhile, despite WP's recognition of other specific articles on signals using other forms of expression.

Are these your positions? Brews ohare (talk) 17:33, 13 April 2012 (UTC)

No, I don't think there's a need for an article on the general term, i.e. on the general meaning of 'signal'. Such an article is not an an encyclopaedic one on a particular topic, and users are best served by the disambiguation page which lists different topics clearly and concisely so they can find the one they need (or the link to wikt:signal if they are just unsure of the meaning). I have answered the other questions already.--JohnBlackburne^words_deeds 18:38, 13 April 2012 (UTC)

I didn't ask any questions, so I take your answer as saying that I have correctly understood your positions as described by point 1-3 above? Brews ohare (talk) 18:53, 13 April 2012 (UTC)

Again, I have made my points, and I'm sure you can read what I've written. You should not try and summarise other editors arguments in your own words.--JohnBlackburne^words_deeds 19:17, 13 April 2012 (UTC)

Hi John: Not trying to put words in your mouth: you're invited to restate things as you wish them to be. I just found your original statements unclear.

The info at Signal (communications) is far more than a dictionary entry, and putting this material as a general article makes it available to the general interest reader, instead of a paragraph or two packed into a specialist topic that the general reader might not wish to consult, like Signal (electrical engineering). Brews ohare (talk) 21:47, 13 April 2012 (UTC)

I would pretty much agree with the 3 points that Brews is testing above, except for the red herring about smoke signals I don't see why he keeps bringing up (there's nothing in the article about smoke signals, so it's just a hypothetical). The article that he separated out is just an intro paragraph and a list of some types of signals that EEs work with, so it fits better here than in a fork. And I don't see that an article specifically on electronic signals would have much to add, though I suppose it's possible; probably it's better to add to this article until it becomes clear that a split is needed. Dicklyon (talk) 00:38, 14 April 2012 (UTC)

OK Dick: I see that you and Blackburne are in agreement that the wide-ranging nonsense about "signal" in Signal (electrical engineering) is just great, even though its reference to "words flowing into the reader's mind" and "systems existing in the physical world – either living or non-living" are simply ludicrous. What changes are you willing to see made in this crazy text? Maybe you would agree to substituting the first section of Talk:Signal (electronics)/Signal (communications) for the present (shall I say) mawkish verbiage in Signal (electrical engineering)? Brews ohare (talk) 04:14, 14 April 2012 (UTC)

I'm not sure what you mean by "wide-ranging nonsense". I haven't really studied the article in recent years, nor expressed an opinion on its quality. It's a tough topic, with fuzzy bounds. You could probably help a lot with some tweaks to those parts you pointed out. If you think a wholesale replacement of the lead is in order, that will need a closer look. Dicklyon (talk) 04:18, 14 April 2012 (UTC)

OK, I rewrote the intro. Take a look. Brews ohare (talk) 04:40, 14 April 2012 (UTC)

I tweaked it a bit, as yours seemed too narrowing. Dicklyon (talk) 05:20, 14 April 2012 (UTC)

Section "Examples of signals"

Now that the intro is better, let's look at Examples of signals. IMO many of these statements are almost wrong, and poorly phrased. Brews ohare (talk) 13:28, 14 April 2012 (UTC)

To take these one at a time:

• Motion. The motion of a particle through some space can be considered to be a signal, or can be represented by a signal. The domain of a motion signal is one-dimensional (time), and the range is generally three-dimensional. Position is thus a 3-vector signal; position and orientation is a 6-vector signal.

Is this a signal in the sense of this article Signal (electrical engineering)? It sounds more like a signal in the sense of street shootings. Where is the source for this attribution as a signal in EE? Brews ohare (talk) 13:32, 14 April 2012 (UTC)

Here is a possible discussion and source for this topic. Brews ohare (talk) 13:53, 14 April 2012 (UTC) Here is another. Brews ohare (talk) 13:55, 14 April 2012 (UTC)

I'd say that in the sense of EE, the motion is detected, say by radar, and it is the detecting mechanism that provides the signal. In other words, the motion is the original signal, but it is converted to an EE signal by a transducer, like reflection of a radar beam. How can this sentence be rewritten to make more sense? Brews ohare (talk) 14:03, 14 April 2012 (UTC)

I've rewritten this section to emphasize the part played by sensors as transducers. Brews ohare (talk) 14:34, 14 April 2012 (UTC)

I don't think you should let the title drive you into thinking that the topic is "EE signals", whatever that is. EEs deal with real-world signals all the time. Dicklyon (talk) 16:26, 14 April 2012 (UTC)

Proposed merger

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

---

I propose merging Signal processing into this article because

• Signal processing is effectively a stub, and shows no sign of growing into a substantial article.
• If both Signal (electrical engineering) and Signal processing were developed into PERFECT articles, they'd overlap each other substantially (90%?).
• Digital signal processing and Analog signal processing articles also exist (and DSP is a substantial article), to carry on in greater depth about the techniques of signal processing.

-- The Photon 04:24, 10 June 2006 (UTC)

I think they're distinct enough content areas to keep separated. The signals article talks about different types and classifications of signals, how the term is used in different fields (some of which, like information theory, have someswhat different usess than the broad signal processing field), and stuff like that. The signal processing article is more about techniques and application areas. I think merging them would be messy. Dicklyon 17:57, 10 June 2006 (UTC)

The Signal processing article doesn't talk about any of that. Everything that's currently in that article would fit comfortably in this one.

Digital signal processing does discuss the techniques and applications, and Analog signal processing could but its also just a stub. So my proposal is to give the top level overview in Signal (electrical engineering), and put applications and techniques information into the more specific "Digital ..." and "Analog ..." articles. From your input, I might change my above reasoning (2nd bullet) to say, "if Signal processing were developed into a PERFECT article, it would overlap almost entirely with either Signal (electrical engineering) or Digital signal processing or Analog signal processing."

There's a sideline or tangential issue that Analog signal processing is not a common term (at least in my experience), and Filter theory or Filter or Analog electronics would be better titles for that article.

-- The Photon 05:21, 11 June 2006 (UTC)

I agree that there's a lot of overlap in the topics covered. However, signal processing is such a basic subject... I just don't think it would look right if someone were to search for signal processing and be redirected to some other article. Wouldn't it be better if the final article were called Signal processing, rather than Signal (electrical engineering)? Don't you think the former is a more common search term? --Zvika 17:01, 12 June 2006 (UTC)

If I was sole editor of a traditional encyclopedia, I'd probably rather do it that way. There's so many different ways to define the word signal that each subject area should just treat the topic within its own article. But for Wikipedia, there's a couple of reasons to do it the other way around:

• Editors of other articles will want to be able to make a link to Signal more often than to Signal processing. If that article doesn't exist, someone will re-create it.
• It's clear (maybe just to me) that signal processing is a subtopic of signals, but not obvious that signals are a subtopic of signal processing. It's possible to have signals without signal processing, but not the other way around.

But, I could go either way on this. -- The Photon 02:40, 13 June 2006 (UTC)

I prefer having separate articles. This article should be about the basic concept of the signal and its types. "Signal processing" should be about the field and its branchs and basic techniques. I don't think that there will be much overlap. Even if we merge them now, we will eventually need to split them. BorzouBarzegar 13:12, 13 June 2006 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Requested move 3 April 2017

The following discussion is an archived discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. No further edits should be made to this section.

Moved to the primary topic; there is clear consensus for a broad concept article based on this existing article to serve as the primary topic of this term. The existing disambiguation page for topics not covered by the broad concept article (such as album titles) will automatically be moved to Signal (disambiguation). bd2412 T 00:32, 17 April 2017 (UTC)

Signal (electrical engineering) → Signal (information theory) – The target article covers the topic of signals more broadly than just an electrical engineering context. The proposed target captures the full meaning of the term. —swpb^T 13:41, 3 April 2017 (UTC) —swpb^T 13:41, 3 April 2017 (UTC)

• Oppose – the way I look at it, and as the article says, the field of information theory is about the information content of signals; essentially, a narrow statistical view; and that the field of electrical engineering, in spite of its obsolete name, takes a broader view of signals. Dicklyon (talk) 00:46, 4 April 2017 (UTC)
• Support, it seems to me that information theory covers more uses than electrical engineering. A signal is a way of communicating information, and while this article explicitly mentions computers, can be completely separate from electronics. The signal disambiguation page gives this page's definition as: "a function that conveys information about the behavior or attributes of some phenomenon". Also, the signal processing subarticle specifically defines at as extracting information from a signal. Laurdecl ^talk 08:05, 5 April 2017 (UTC) see below. 03:15, 8 April 2017 (UTC)

• Make primary Support as a good first move. I would even go further and suggest we should consider if it should be edited and extended somewhat and moved to signal as the primary topic, or if not, a new top level article should be created to fill that role.GliderMaven (talk) 15:52, 5 April 2017 (UTC)

@GliderMaven: I too believe that this should be the base page, as detailed in WP:DABCONCEPT. If this move goes ahead, I'll probably do it... Laurdecl ^talk 06:22, 6 April 2017 (UTC)

Changed vote to make primary, the opposers seem to be reading completely different articles and dab pages to everyone else.GliderMaven (talk) 14:50, 11 April 2017 (UTC)

• Make primary: I support the proposal that this article should be moved to Signal.--Srleffler (talk) 02:17, 8 April 2017 (UTC)
• Make primary per my comments above, GliderMaven, and Srleffler. Laurdecl ^talk 03:15, 8 April 2017 (UTC)
• Oppose the original proposal is not a clear improvement over the current title and I am opposed to changing things without clear benefit. Moving this article to Signal is a more interesting proposal. Presumably the current contents of Signal would move to Signal (disambiguation) under that proposal. Unfortunately, I really can't support this proposal either because of the number and diversity of topics I see listed Signal (disambiguation). There may be a good case for having a non-disambig Signal article but Signal (electrical engineering) is not, at present, ready to be promoted there. ~Kvng (talk) 18:12, 9 April 2017 (UTC)

I, and supposedly others, see it as a good example of WP:DABCONCEPT. There are many different articles on the DAB, but they all deal with a subset of the information theory concept. Laurdecl ^talk 23:45, 9 April 2017 (UTC)

• Make primary, i.e. move to Signal as WP:DABCONCEPT (and consequently Signal → Signal (disambiguation)). Barring that, support the move as proposed as second best choice. No such user (talk) 14:39, 10 April 2017 (UTC)
• Comment re PRIMARYTOPIC – obviously we would need a wider discussion if we wanted to grab primarytopic status for this particular signal. It seems unlikely to me that it has any kind of majority traffic or important relative to all the others. The new RM bot mod will notify all the affected pages if we make an RM to move the dab page. Dicklyon (talk) 14:50, 10 April 2017 (UTC)

Not really; I'm sure the closer can judge the consensus here and make the right move, another RM would be a waste of time. The argument for WP:DABCONCEPT seems strong to me. Laurdecl ^talk 07:05, 11 April 2017 (UTC)

• I would support creating a WP:CONCEPTDAB at Signal, whether we rework this article to serve that purpose or create a new one. As stated above, there's a core definition of "signal" that this and other articles rely upon (such as Audio signal, Maritime flag signalling, Signaling (telecommunications), Signalling theory, Cell signaling, and very many others), but which we don't have clear coverage of anywhere. None of the unrelated topics titled "Signal" (such as the songs and albums of that name) could conceivably compete in terms of long-term significance.--Cúchullain ^t/c 15:05, 11 April 2017 (UTC)

The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page. No further edits should be made to this section.

Note: A good deal of work will need to be done to make this article more encompassing of signaling occurring in the natural world, and in low-tech ways in the human world. bd2412 T 00:45, 17 April 2017 (UTC)

This excerpt matter needs to be emphasized in the Article

Signlal Transformation is study of understanding how exactly Signal works when it comes to level which we study on & around object which expels gravity and hold some signal, at levels by height & width which cannot be taken in x and y axis, abscissa and mante i.e., Abscissa and Ordinate.

However Signal is very defaulted one and has the expected behavior which cannot be calculated precise even when we multiplex, modulate and demodulate, however we can achieve what we require to achieve when distance from object changed all changes unprecedentedly and goes on to different setting by completely to Else.

However field principles are by Signal. We can get to the place and do Or ∨ and And ∧ principles, other Boolean ops also allowed, but linearity cannot be entertained always. Also not all Matrix Linear operations can be used to find co-efficient(s) that works effectively.

Non-Linearity is defaulted in all Physical Principle Object. But the above is the way to intrude, intricate and make inference to Any.

—Dev Anand Sadasivam^t@lk 17:50, 8 November 2017 (UTC)

Definition fodder

The lead of Signal processing has some good referenced definitions for signal. This bit was added anonymously. I have removed it. Perhaps it can ripen here and be included in the Definitions section of this article if deemed appropriate. ~Kvng (talk) 13:51, 8 September 2018 (UTC)

A new definition of signal excludes images or similar entities, which are only functions of space, from the category of signals.

That might be a new technical definition of the term, but it is not the everyday human experience of a signal (as in "wait for my signal"). bd2412 T 14:08, 8 September 2018 (UTC)

References

The new definition is certainly technical and it has been included in the description of signal processing which by itself is technical; i.e the topic signal processing is not an everyday human experience either. The new definition has been published in the highest impact factor journal of the IEEE signal processing society and it has been established after rigorous reviews by some experts in the area of signal processing. I think one should appreciate the fact that definitions should not come into existence because of some petty phrases and sentences like 'wait for my signal'. As a responsible contributor, I have reinstated the definition and its reference. However, whether images or similar entities should be considered signal or not is left onto the readers to decide after reading the complete article. Therefore, only the definition has been written whereas the interpretations are not reinstated.- Pragnan Chakravorty — Preceding unsigned comment added by 220.225.206.201 (talk) 05:05, 10 September 2018 (UTC)