Talk:Sampling (signal processing)

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Article wrong according to hatcravat

https://news.ycombinator.com/item?id=5581806

I don't know where to start, this is not my domain. --Ysangkok (talk) 15:57, 21 April 2013 (UTC)

I would just leave it alone. This article is factual enough, there are no glaring errors that I can see. There are some analog holdover folks that think that any digitization compromises quality. I think that they are as correct as the monster cable advocates. I dunno. 70.109.185.57 (talk) 16:11, 21 April 2013 (UTC)

Are you sure you read the post by hatcravat? I only linked iso8859-1's post so that you'd see the context. --Ysangkok (talk) 18:16, 22 April 2013 (UTC)

I don't see anything in that discussion that even suggests the article is wrong. Where hatcravat says "This is wrong." he is referring to the original complainer. He's right that he's wrong. Dicklyon (talk) 04:23, 23 April 2013 (UTC)

Theory: no Hz. f_s alsready contains the unit

Two recent edit labels, both attempting to justify the same change:

• Theory: no Hz. f_s already contains the unit (User:Kondephy)
• Neither T nor f_s are dimensionless numbers. And they *may* be expressed with units other than seconds or Hz

are saying two very different things.

The first one touches on a minor issue that is real, but usually glossed over in the textbooks. However the edit label incorrectly identifies that issue, and the "fix" is inadequate. The second one is of course true, but entirely misses the point.

The issue is that the June 5 version of the article makes these statements:

• let s(t) be a continuous function (or "signal") to be sampled, and let sampling be performed by measuring the value of the continuous function every T seconds
• The sampling frequency or sampling rate, f_s, is defined as the number of samples obtained in one second (samples per second), thus f_s = 1/T.
• That fidelity is reduced when s(t) contains frequency components higher than f_s/2 Hz, which is known as the Nyquist frequency of the sampler.

The problem is that the quantity "1" in "1/T" obviously has units of samples, and the quantity "1/2" in f_s/2 has units of cycles/sample. Those statements are what's lacking from the article (as they are from most texts). One remedy is to simply insert them without any reason given, but that's like magic. This article is not a proper place for the whole story, so ideally it would WikiLink to an article that is. And ideally that would be Nyquist frequency, but it suffers from the same deficiency. The closest thing we seem have at the moment is Nyquist–Shannon_sampling_theorem#Aliasing, and this formula in particular:

$X_{s}(f)\ {\stackrel {\mathrm {def} }{=}}\sum _{k=-\infty }^{\infty }X\left(f-kf_{s}\right)=\sum _{n=-\infty }^{\infty }\underbrace {T\cdot x(nT)} _{x[n]}\ e^{-i2\pi nTf},$

where the units of $f$ and $f_{s}$ are again in Hz and samples/sec, and so the integer k must have units of cycles/sample. The Nyquist frequency corresponds to k=½, because that is the midpoint between the k=0 image and its first alias.

It seems like too much information for this article, which is why I haven't done it. But in my edit label I invited User:Kondephy to take it on, in case he/she feels strongly about it.

--Bob K (talk) 12:06, 13 June 2014 (UTC)

No, Bob. You made it worse. You seem to think (or you seem to want everyone else to think) that seconds and Hz are the only possible units to express time and frequency in. They're not. f_s can be expressed in many other units, like kHz or MHz. Maybe even someday, we'll express it in GHz. But it doesn't matter. f_s is not a dimensionless quantity, it is a dimensional physical quantity. Now normally we may want T and f to have reciprocal units (like ms and kHz), but they need not be. You can still have T in ms and f in Hz and their product is still a dimensionless value and it's the same dimensionless number despite the choice of units (as long as the choice of units fall within the same dimension of quantity).

As you have many times before, you made the page worse, but you are more tenacious than I so your confusing and incorrect edit will survive until someone else comes along.

There is so much wrong with nearly every point you make. E.g. cycles/sample doesn't have units. It's dimensionless. Just a number.

And statements like "The problem is that the quantity "1" in "1/T" obviously has units of samples, and the quantity "1/2" in f_s/2 has units of cycles/sample" are so asinine that they deserves no other comment.

Have you ever published in the literature? A textbook or a technical paper that was refereed and edited by someone else? Have you ever written a decently mathematical rigorous treatment of something in, say, electrical engineering? No one can tell (but we might guess the answer is no) by your edits here at Wikipedia, and I have seen your edits screw up pages here for better than 6 years.

I'm 58 years old myself, I imagine that you're even older and stuck in your ways, but it's a shame that fallacious notions misunderstood and doggedly held by old engineers whose ways are atrophied and cannot change, that such confuses other people. Bob, you need to clear your own ignorance and misconceptions before you have hope of doing that for others.

Sheesh.

70.109.184.247 (talk) 17:44, 13 June 2014 (UTC)

I'm sorry you feel that way. I don't know where this discussion will go over time, but I don't expect it will be time well spent. So all I will say for now is that your whole premise, which is: "You seem to think (or you seem to want everyone else to think) that seconds and Hz are the only possible units to express time and frequency in." is incorrect. The article chooses those units to illustrate its points. I quote:

For functions that vary with time, let s(t) be a continuous function (or "signal") to be sampled, and let sampling be performed by measuring the value of the continuous function every T seconds,

It is certainly possible to rewrite the article in more generalized terms, but that is not what you did. You kept the definition of T and then just ignored it.
--Bob K (talk) 02:05, 14 June 2014 (UTC)

Some reorganization

I propose to merge Discrete-time signal into this article and also the material in Digital_signal#Discussion that was recently split from Discrete-time signal by Fgnievinski. This will put description of the signal that results from sampling in context of the process that creates it. Covering Discrete-time signal comprehensively will result in a lot of unnecessary overlap with this article (Sampling (signal processing)). Removing Digital_signal#Discussion from that article will allow Digital signal to be about one topic - the pulse train signals used for digital logic. Digital signal is now part disambiguation and part article which is not good. ~Kvng (talk) 15:14, 25 July 2015 (UTC)

I would oppose such a merge. There are other ways to get discrete-time signals than by sampling continuous-time signals. These are distinct topics. 73.158.249.163 (talk) 03:16, 26 July 2015 (UTC)

Can someone give me an example or two of the other ways to get discrete-time signals. Discrete-time signal lists two but they are both sampling. ~Kvng (talk) 13:18, 28 July 2015 (UTC)

I agree with relocating Digital_signal#Discussion to allow that article to focus on digital logic. But I also prefer to keep it physically separate from this article, connected by a WikiLink. A more appropriate location is Quantization (signal processing), and I have attempted that merge. But I have not yet removed anything from Digital_signal.

Discrete-time signal is more like a handy definition than an article, which is very useful (see WhatLinksHere). I think that list is sufficient justification for the article's independence, and I don't think it needs to grow and cover the topic comprehensively, because it can WikiLink back here (and elsewhere) for that. Also, the Discrete-time_signal#Acquisition section, which makes a valid distinction between sampling a continuous function vs observing an inherently discrete process, doesn't really need to be here. I think it is better off encapsulated where it is.

--Bob K (talk) 17:46, 29 July 2015 (UTC)

Do you have a suggested destination for relocating Digital_signal#Discussion?

I've done a bit of cleanup in this topic area and discovered another overlapping article: Discrete time and continuous time. Any opinions about this material? ~Kvng (talk) 21:01, 29 July 2015 (UTC)

My suggestion was Quantization (signal processing), and (as I said above) I have already done it. It is not just a cut & paste merge. It is a blend, in the interest of coherence.

I just took a quick look at Discrete time and continuous time. IMO, it's not very interesting. I would probably support a movement to delete it. But if others find it useful, I'm happy to just leave it alone.

--Bob K (talk) 16:12, 30 July 2015 (UTC)

You have done some work on Quantization (signal processing) but Digital signal has not been changed. ~Kvng (talk) 16:58, 1 August 2015 (UTC)

A related topic is that the What Links Here list for Digital_signal has 309 entries, and oddly, Digital Signal Processing is not one of them. Perhaps the name "Digital Signal" is a misnomer. Would "Boolean signal" or "Data signal" be more appropriate? It is hard to tell what those 309 links are trying to reach, because Digital_signal is about two very different topics. If we purify it, by removing the sampling/quantizing parts, how many of those 309 links will lose the content they wanted?
--Bob K (talk) 15:54, 1 August 2015 (UTC)

I think it is best to move and continue this discussion at Talk:Digital_signal#Two_topics ~Kvng (talk) 16:58, 1 August 2015 (UTC)

Hint for Audio Studio, Nyquist-Theorem

44.1 kHz is considered fine (per timed sample) enough, to get an exact impression in the human ear, but:

If you got several digital instruments, and their output DACs use a 44.1 kHz Sampling Rate, i would suggest a 88.2kHz recording samplerate. See Nyquist Theorem (Sampling Frequency).

If you got high quality DACs and ADCs, the same sampling rate could give good results too, even if the converters work unsynced (because the energy potential flows "analog").

MfG, Hannes E. Schäuble

PS: Yes, sometimes you hear the difference between 44.1 and 88.2 kHz ;) e.g. "natural" overtones etc.

And yes, some musicians do use frequencies you can't head with your ear , but bones etc. intentionally. Sad if they are lost. (e.g. Sub-Bass in old Church Pipe Organs)

MS/s

I was redirected from a page named "MS/s" [1]. I think it means Mega-Samples per second, but want to confirm. Unfortunately, the units S/s does not appear anywhere on the page. Anyone know the answer? — Preceding unsigned comment added by 2400:DD01:2000:15:18F4:FB1D:F641:5A3F (talk) 08:06, 4 July 2016 (UTC)

I added it to the page. Correct if wrong!