# Talk:Frequency

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## 440 Hz

some think thisIs it not true the A tuning note is only 440 Hz in the United States, while in fact 442 Hz in Europe? Perhaps this should be changed.

See Pitch (music)Omegatron 14:36, 20 February 2006 (UTC)

## Changing wavelength

I was just wondering about the comment that when a wave goes from one medium to another, the frequency remains more or less the same, only the wavelength changes -- this doesn't make sense to me. If frequency has an inverse relationship to wavelength, how can one change without the other?

It's correct. Suppose the wave propagates 340 metre per second in the first medium, and 680 m/s in the second, and suppose the frequency is 340 hertz so that the period (i.e. the time it takes for one complete oscillation) is 1/340 seconds. These values fit a sound (a rather deep tone) passing from air into a somewhat harder medium. Then, in air, this sound travels 1 metre per period, so the wavelength is 1 metre. In the harder medium, it will travel 2 metre in the same time, doubling the wavelength.

Put differently: Yes, frequency has an inverse relationship to wavelength in a given medium, but the constant of proportionality depends on the medium.--Niels Ø 09:35, Apr 15, 2005 (UTC)

## Invariance of frequency

Just wondering if any one has thought about why frequency is invariant (apart from doppler effect). ie whatever you do to a signal, you can change its wavelength and or velocity but you cant change its frequency. (I'm not considering mixers here). Any musings from anyone as to why this should be so?? --Light current 06:52, 23 November 2005 (UTC)

Because it's based on time? Theory of relativity and all that?
I'm not sure if it's worth pointing out, but the frequency of a pre-recorded signal can certainly be changed by playing it back at a different speed. Practically, if you sample something with an incorrect sampling frequency (you think it's 48 kHz but the oscillator's actually running at 48.01 kHz), then reproduce it correctly, the frequencies will be shifted.
Plus there are things like pitch shifters to simulate a change in frequency, though that's even less relevant. — Omegatron 21:32, 7 December 2005 (UTC)

Quite correct about pre recorded signals, but Im thinking more of a 'pitch shifting' method but broad band and not using mixers (multipliers). I guess it just can't be done? --Light current 22:07, 12 December 2005 (UTC)

It could probably be done with wormholes. :-) — Omegatron 15:02, 18 February 2006 (UTC)
I've heard that strong gravitation could change the frequency, so wormholes, why not :)
Oh you're right! You could change frequency just by flying around at a different altitude from your observer. Gravity Probe A was exactly that. — Omegatron 02:22, 7 June 2006 (UTC)
This is a Doppler effect. GoldenBoar 16:13, 7 June 2006 (UTC)
I don't think so. Time flows at a different speed depending on your distance from the Earth or another body. If you took a huge loudspeaker and put it in a hot air balloon, time would pass at different rates for you and the speaker, so the frequency would be shifted, since frequency is really just another word for time. — Omegatron 23:21, 7 June 2006 (UTC)
What about the Invariance of Speed, with regard to a constant medium? The above discussion and corresponding paragraph in the article both make some broad assumptions about the source of the Waves. It is also true that if the medium remains the same, speed is invariant with regard to wavelength and frequency... That is, if you have a slinky... and start sending pulses through it at a fixed speed, changing the frequency with which you initiate the pulses will only affect the wavelength, and vice-versa (i.e., frequency is NOT invariant). Representing this fact as well would probably make the article more sensible-seeming to those who really don't know anything about waves. I mean, strictly speaking, since the article is a general description of the quantity Frequency, with respect to other common quantities or terms used to describe the nature or behaviour of waves and signals - e.g., period, phase, amplitude, wavelength, cycle, etc. - this rather random statement about the Invariance of Frequency is not true, at least not without some context. - joe

I removed from the bottom of the section Frequency of waves:

Apart from being modified by the Doppler effect or any other nonlinear process, frequency is an invariant quantity in the universe.
That is, it cannot be changed by any linearly physical process unlike velocity of propagation or wavelength.


My motivation is:

1. The Doppler effect is a linear process and changes frequency.
You guys probably settled this a long time ago, but Doppler shift is not linear operation the EM field. It is caused by something in motion, and that something in motion means the media constants are functions or time. Suppose a steam engine was over there and now it is over here. When it was over there, the media constants over here were pretty close to vacuum. When the train is here, the media constants differ greatly from vacuum. The moving train is in effect a time dependent distribution of the media parameters. E&M propagation is not linear if the media is time dependent. Which, of course we know because it generates frequencies at its output that were not in the input. And if you are more into math, sine waves are Eigen functions of linear time invariant differential equations. Constant314 (talk) 21:08, 29 October 2010 (UTC)
1. The statement is contradictory since it states frequency is invariant but it can be changed by the Doppler effect.
2. The statement depends on the definition of frequency. If using, for instance the Fourier transform, frequency is the new independent variable and will be invariable since it is independent. I do not know any other definitions of frequency, e.g. the time derivative of the phase, which leave it in general as an invariant (apart from trivial cases as periodic oscillations).

Kraaiennest (talk) 17:07, 22 February 2008 (UTC)

## Measurement

We have a rather strange paragraph that tells us how to measure frequency by dividing one number by another which is of course true. But do we have anything about various classes of frequency meter - i.e. how we actually measure frequency? Pcb21 Pete

Yes, that would be a good addition, aince there is no separate article for that topic. --ChetvornoTALK 19:52, 8 August 2008 (UTC)

In my opinion, this is not a unit of frequency, but of angular frequency. --84.159.248.246 17:04, 20 November 2006 (UTC)

## Human heartbeat

I removed the non sequitur "Notes" heading and its entry about the human heartbeat being close to one Hertz. Actually, the human heartbeat varies quite a bit--it can get down to 0.8 Hertz in mellow marathoners and up to 2 Hz in times of high stress activity. Average heart rate is about 72 bpm, or 1.2 Hz. No studies support the statement that the heartbeat is exactly 60 beats per minute which means there's no benefit to the reader by announcing that the heartbeat is approximately 1 Hz. It doesn't shed any light on the concept of frequency. Binksternet (talk) 08:36, 25 January 2008 (UTC)

## Period estimators (for ocean surface waves, copied from Talk:Wave period

Mean zero up-crossing period, TZ or Tm0,2

## Wireless communications

I have removed the following from the "Definitions and units" section:

Frequency is important in wireless communications, where the frequency of a signal is mathematically related to the wavelength. If f is the frequency of an electromagnetic field in free space as measured in megahertz, and w is the wavelength as measured in meters, then w = 300/f and conversely f = 300/w

(1) The text, if it belongs in the article at all, is in the wrong section. The text does not belong here. There is a long list of things for which the concept of frequency is important, we aren't going to talk about all of them in the "definitions and units" section. (2) The text is true but not true enough: (2a) With waves speed is always "mathematically related" (i.e. equal to the product) to frequency and wavelength, that fact is not specific to "wireless communications". (2b) The 300 used is the speed of light in a vacuum, although we neglect to mention that point, but this isn't the page for quick rule-of-thumb formulae for radio technicians. (2c) Elementary maths gives us one formula from the other so, once again, not useful here. (3) Everything is already covered in the "physics of light" example section.

Paul Beardsell (talk) 19:22, 15 March 2009 (UTC)

## Put 'Physics of sound' section on a diet

I think most of the 'Physics of sound' section should be removed. Description of longitudinal vs. transverse waves, polarization, etc. are not necessary for the explanation of frequency of sound waves, and simply repeat coverage in other articles. This is where 'Wikipedia bloat' comes from. All that should appear is a simple exposition of sound wave frequency, mention of how it's measured, and maybe something on the 'spectrum' of sound frequencies analogous to the spectrum of electromagnetic waves. --ChetvornoTALK 22:58, 17 March 2009 (UTC)

I couldn't disagree more. There are far too many articles on audio equipment and acoustics and music that link to this page expecting it to explain what frequency has to do with sound. I recently added information about pitch, because it wasn't there and I needed it.--Atlantictire (talk) 03:04, 1 May 2011 (UTC)
Done. But see new section below. Dicklyon (talk) 17:55, 18 January 2014 (UTC)

## Vandalism

The last citation link links to xkcd for absolutely no reason. —Preceding unsigned comment added by 71.228.164.178 (talk) 02:25, 9 June 2009 (UTC)

XKCD are currently running a campaign to vandalise the wikipedia of every subject the comic touches upon. —Preceding unsigned comment added by 217.23.232.41 (talk) 15:47, 10 June 2009 (UTC)

No. Firstly, assume good faith. Secondly, xkcd is a comic (singular) and not a corporation, team or trained knowledge-fighting force all bent on destroying wikipedia. 217.23.232.41, you have yourself proven to be attributing more troll-like behaviour, having recently launched your own "one soldier counter offensive" and posting anti-xkcd pseudo rants on all talk sections of articles pertaining to or mentioned by the webcomic. I'm not in favour of more xkcd refs on WP, I'm just wondering who really has the problem here. --PenguinCopter (talk) 10:15, 12 June 2009 (UTC)

## Fourier analysis

Frequency in Fourier analysis is a different concept from 1/(period). I don't have time to write an explanation now but I think that concept, and links to appropriate articles, would be helpful here. Ccrrccrr (talk) 23:25, 19 February 2010 (UTC)

## It depends!

Please add some data to the article saying what variables of waves in sound and light depend on the frequency of the wave. eg speed, impedance, refracting index, attenuation coefficient, etc. —Preceding unsigned comment added by 91.99.166.67 (talk) 10:50, 10 May 2010 (UTC)

## Frequency and perception info in lead

There ought to be an overview of how frequency is relevant to your perception of, say, light and sound in the lead. I can't tell you how many audio-related pages link to this one, expecting it to explain how frequency is the property of sound that most determines pitch. Until just now it didn't. I've added a very brief explanation of frequency's relationship to pitch in the Physics of sound section.

But, I think this ought to be stated in the lead as well so that readers will know why they'd been linked to the frequency page right away.--Atlantictire (talk) 20:59, 26 April 2011 (UTC)

I think that's too much detail for the lead paragraph; most of the knowledge about pitch and color was worked out long before we had the ability to measure "cycles per second", and frequency isn't really a sole determinant of color; "white" is very important to color, but "white light" doesn't have a frequency, it has a spectral distribution over a whole range of frequencies. The color of a pair of socks is not uniquely determined by any particular "frequency" but by the complex interaction of light, the optical properties of the material, and the human vision system. We have sections just a short distance below the lead that explain in detail. I would suggest that any mention of color or pitch not imply that "freqeuncy" of light or sound is the unique determinant. We can't teach all of physics to someone standing on one foot, but we shuold at least avoid a quick 'n'dirty statement in the lead that is going to take paragraphs to unwind and correct later. Have you got a suggested wording? --Wtshymanski (talk) 16:14, 28 April 2011 (UTC)
Ah ha. Excellent points. To be perfectly honest, I am thinking of the needs of people who read articles on audio and I know nothing about optics, but it in broad overall principle it sounds vaguely similar to sound wave perception. Room acoustics and neurocognitive factors play a very important role in how pitch is perceived, but controlling for all that stuff, frequency is the property of sound waves that most determines pitch. Are there other properties of light waves (or whatever you call them!) that determine color, and are they as important as frequency? Sound pressure can affect pitch perception, but it's influence is secondary.
How is this: "Frequency is the property of sound waves that most determines pitch, and as a property light it plays an important role in determining color."--Atlantictire (talk) 17:08, 28 April 2011 (UTC)
Sure, try that in the article and let's see what consensus tells us. It's better because it doesn't implicitly equate frequency and color. --Wtshymanski (talk) 17:40, 28 April 2011 (UTC)
The trouble is, it's not right. It says "Waves, such as sound waves or light waves, are oscillations, and therefore they have a frequency (or frequency spectrum)." But there's no support for this; the Wave page says a wave is a propagating disturbance; there's no particular reason why a wave would be an oscillation, or be periodic, or have a frequency. And having a frequency spectrum is a much more complicated concept, which doesn't accord well with the topic, nor does it support the sentence that follows, which presumes the existence of a frequency. Dicklyon (talk) 15:14, 1 May 2011 (UTC)
Your suggested alternative wording is? Light waves and sound waves are propagating oscillations and I suppose then a subset of "waves". --Wtshymanski (talk) 15:40, 1 May 2011 (UTC)
I made a change in the lead already. Light waves and sound waves are propagating disturbances, and are waves, but are not necessarily "oscillations" in the sense that means periodic and having a frequency. Dicklyon (talk) 15:45, 1 May 2011 (UTC)
I tried again [1]...any better? --Steve (talk) 20:53, 1 May 2011 (UTC)
I'd prefer to have the lead stay simpler, and strictly truthful. To introduce Fourier transforms and spectra here is not a good idea; a section in the article about that would be OK. But it would be better not to say untrue things like "Any time-varying disturbance... can be alternatively described in terms of a frequency spectrum, given by the Fourier transform of the original signal." There are conditions under which the Fourier transform exists, and conditions under which it doesn't; it doesn't exist, for example, for a stationary noise signal, nor strictly for a sinusoid (you can extend it to include delta functions to allow the latter, but that doesn't help the former). And there are severe limits on the extent to which a Fourier transform has much say about a sound's pitch, too. I'd be happy to expound on these problems if you like. Dicklyon (talk) 21:40, 1 May 2011 (UTC)
OK. I'm not particularly happy with the paragraph but I can't think of any way to improve it. :-) --Steve (talk) 00:38, 2 May 2011 (UTC)
──────────────────────────────────────────────────────────────────────────────────────────────────── I would have thought any real sound or visual signal will necessarily have a Fourier transform;that non-transformable signals only exist in math texts. --Wtshymanski (talk) 01:58, 2 May 2011 (UTC)
If by real world you mean finite in duration and finite in amplitude, then yes, it will have a Fourier transform. But it won't be useful, in general, and in particular won't have any feature identifiable with pitch, for most sounds. Basically it's a periodogram, which is pretty badly behaved; it's sort of OK for light of a constant color, and perhaps of some use for a sound of a constant pitch, but not much good for a real sound like a song. Anyway, having a Fourier transform is still remote from having a frequency, and getting into spectrum in this article is probably outside its scope. Dicklyon (talk) 03:47, 2 May 2011 (UTC)
Let's see, there's nothing older than the Big Bang, and nothing farther than mumblety-million light years, so yes, I guess I do mean finite in time and in amplitude. I was more concerned with the condition of finite numbers of discontinuities, actually, but those other attributes help. We can't hear DC or see DC, at any rate; gotta be oscillating to be heard, and the ear is its own Fourier analzyer. I don't care to speculate on what other Wiki editors call the real world as my notions of what they consider real and notable seem to have low utility for predicting their behavior. Do we really need all that ponderous oscillation stuff in the lead? --Wtshymanski (talk) 14:06, 2 May 2011 (UTC)
The proposed alternatives have been to rely on Fourier transforms, or to rely on the assumption that all waves are oscillations that have a frequency. I don't see how either of those could be seen as an improvement. What else you got? What, by the way, is the frequency of the sound entering your ears (it's OK to truncate at your birth and your death). Dicklyon (talk) 15:08, 2 May 2011 (UTC)
Oh very good. This is exactly how we'd explain it to the first-year physics class. We don't need Fourier transforms at all (in the lead), and I'm not convinced there's no sound or light that aren't waves. But aren't you also concerned we've left out the relativistic corrections that are such an important feature of so many Wikipedia articles? We must beat the reader to death with every conceivable qualification and limitation in the lead; othjerwise there's the chance they won't be overawed with our smartness. --Wtshymanski (talk) 15:23, 2 May 2011 (UTC)
Wtshymanski, could you copy-and-paste some text, or link to an old revision of the article, that you really like? Then we can discuss whether or not it is misleading, and if so whether or not it can be fixed with rewording or links or footnotes or whatever. :-) --Steve (talk) 06:27, 3 May 2011 (UTC)
Good idea, climbing down the ladder of abstraction usually helps focus the discussion. I prefer something like [2]. We should not equate frequency of light with color perception, we should not go off on a tangent about non-oscillatory sounds (whatever that could be), and we must not drag in the whole mathematics textbook in the lead section. I don't like "helps determine", abstract concepts are not Boy Scouts helping little old ladies across the street. Freqeuncy is perhaps the major factor in determining (the perception of) pitch, but it's not absolute. --Wtshymanski (talk) 13:43, 3 May 2011 (UTC)
Well, I think I'll let you guys handle it. I'm too conflicted, as I spend a large part of my professional life in hearing research where I'm constantly trying to deconfuse people about frequency versus pitch, so this has become a hot button for me. My favorite quote: "...dehydrated cats and the application of Fourier analysis to hearing problems became more and more a handicap for research in hearing" (von Bekesy). Dicklyon (talk) 15:27, 3 May 2011 (UTC)

Dicklyon, I doubt you're conflicted in a bad way and I hope you reconsider.

The quote is:

P1 "The frequency of a sound wave helps determine its pitch, while the frequency of a light wave helps determine its color."

The main problem that I see is that if the sound wave is, say, five seconds of human speech, it doesn't really have a pitch and it doesn't really have a frequency. Another problem is that people who don't know how sound work will wonder what it means for sound to have a frequency. So then I thought, how about

P2 "The frequency of an oscillating sound wave helps determine its pitch, while the frequency of a light wave helps determine its color."

This sort of answers my first complaint above but not the second. Anyway, this isn't very good because "oscillating sound wave" probably makes people think of like tremolo or vibrato, which is totally different. Another problem is that, even if the waveform is exactly oscillatory, the oscillation frequency is not necessarily related to the pitch...for example when you play two pure tones together, the waveform oscillates at the beat frequency, but you can't hear the beat frequency at all if it's in the audible range. So then I thought

P3 "When air pressure oscillates sinusoidally, it corresponds to a sound wave called a pure tone. The frequency of the air-pressure oscillation determines whether the human ear can hear it, and if so, the frequency determinnes the pitch of the tone, with higher frequency giving a higher-register pitch. Likewise, when an electric field oscillates sinusoidally, it corresponds to an electromagnetic wave called monochromatic. The frequency of the oscillation determines whether the wave is visible light, infrared light, a radio wave, etc. In the case of visible light, the frequency determines the color, with lower frequency corresponding to red and higher to violet.

OK, now this is accurate I think...but maybe too many words and too many new concepts for readers ("what does sinusoidally mean?, etc...") Or maybe it's OK? Or maybe a better approach is to take P1 and just slap a giant footnote on it... I'll think more later. :-P --Steve (talk) 01:54, 4 May 2011 (UTC)

Oh yeah, P3 is the Wikiest one of all. And everyone knows the frequency of a sound must be determined at the Big Bang and never change until the end of time. Let's try and work in the Doppler effect and at least first-year relativity, too, while we're at it, and make it perfectly general. (To make it even Wikier, maybe add Tesla in somehow.) --Wtshymanski (talk) 02:30, 4 May 2011 (UTC)
For sound waves, the pressure can't change instantaneously - define "frequency" as "time rate of change of phase" and you can get the notion that an "instantaneous frequency" can be defined for every instant (ok, maybe not uniquely). Every sound you can hear is just a 1000 Hz carrier that started at 4:13 AM UTC, July 17th, 4350 BC, suitably modulated! --Wtshymanski (talk) 15:03, 4 May 2011 (UTC)
Wtshymanski, please stop being sarcastic. You can just say "P3 is too technical and readers will be lost". In fact I agree with that. :-) How about:
P4 "The frequency of a sound wave (an oscillation in air pressure) helps determine its pitch, while the frequency of a light wave (an oscillation in electric and magnetic fields) helps determine its color.[NOTE 1]
[NOTE 1]: This is a simplification, valid if the wave is sinusoidal (a pure tone for sound or a monochromatic light wave). For more complicated waveforms, the perception of pitch and color is related more specifically to the Fourier transform of the waveform over a short time interval.
I think this answers both of the problems I pointed out above. "Note 1" is a footnote and would go in a separate footnote section, like they do in this article-section [3]. --Steve (talk) 17:39, 4 May 2011 (UTC)
Not sarcasm, just another observation on how the group-think editing model usually produces unreadable prose; it's not confined to this article, it's a common Wikipedia fault. How about "The frequency of sound relates to its pitch, and the frequency of light is the most important factor in the perception of color." (as distinct from ampitude, say) or something like that. Never mind the waveforms and Fourier transforms, Aristotle and Newton had the gist of the properties of color and sound worked out well before the maths came along. --Wtshymanski (talk) 18:18, 4 May 2011 (UTC)
So you don't like the idea of having a footnote? Why not? I like how you made it sound more vague ("relates to"), that way people will continue to look for more details if they need to know more details.
Do you think it's a problem to say "the frequency of sound", when it's not obvious that sound has anything to do with oscillations? I mean, when you hear a long musical note, it sounds like a constant stream of sound, so isn't it weird to say it has a frequency? Frequency was just introduced in the previous paragraph as something related to periodic oscillations, so intuitively the concept of "frequency" seems unrelated to a constant stream of sound. Imagine you don't know how sound works, then you would read the phrase "the frequency of sound" like you or I would read the phrase "the frequency of a pencil".
On the other hand, I suppose it can be OK and sometimes necessary to have poorly-explained things in the introduction, which are explained better later in the article.
By the way, I have the same goal as you: Clear and pedagogical and easy-to-read and accurate text. I don't think many wikipedia physics articles achieve this, and I try hard to improve them bit by bit. I hope I'm successful most of the time, even if I sometimes make bad edits. Please stop bringing up the sorry state of wikipedia science articles in general, because it sounds like you're blaming me and Dicklyon personally for every bad science article. I doubt that's your intention, but still...let's please just discuss the frequency article. :-) Thanks, --Steve (talk) 01:16, 5 May 2011 (UTC)
Steve, I don't think it's possible for W to talk w/o sarcasm, based on my experience. If you go ahead and try something, he'll tell you if he doesn't like it, but he has a hard time being constructive. So go for it. I don't like footnotes, either, as they too often become a hiding place for unsourced interpretation and rambling. I think that if you have a short thing in the lead that mentions frequency of sound, as long as it doesn't strongly claim that sound has a frequency, should be OK. You can elaborate more carefully later. Dicklyon (talk) 05:04, 5 May 2011 (UTC)
──────────────────────────────────────────────────────────────────────────────────────────────────── If it were only two or three editors , you wouldn't necessarily get the group-think mush; it takes scores of editors to produce the Wikipedia effect at its highest level. It is useful to point out flaws in articles in general so that we can perhaps avoid the flaws in this article. Surely we can explain a basic concept like pitch and color without footnotes? If a relationship is so complex it can't be even mentioned without a forest of qualifications and explanations, maybe it doesn't belong in the lead section at all. "A little inaccuracy sometimes saves a ton of explanation." and I don't think obsessively qualifying the lead paragraph with every historical and relativistic factor helps the lucidity at all. And I've never said a non-sarcastic thing in my life, ask anyone. --Wtshymanski (talk) 13:23, 5 May 2011 (UTC)
I agree with Wtshymanski. A major problem with WP is intros that are mushy, or pedantic, technical, and loaded with qualifying phrases. "It is even more important [in the intro] that the text be accessible." (WP:MOSINTRO) I would say even considering footnotes in the introduction is an indication that it's getting too pedantic. How about something like: "Frequency is also a characteristic of waves, such as sound waves, radio waves, and light waves. It is used to describe the pitch of musical tones and the color of light." --ChetvornoTALK 16:13, 5 May 2011 (UTC)
I like that a little better, and maybe that's as close as we can get...color perception is distressingly complicated but we don't need to get into the problems of color perception in this very peripheral article. --Wtshymanski (talk) 16:52, 5 May 2011 (UTC)
Right. The majority of readers, the ones who need the introduction, are nontechnical readers who are looking for the simplest possible explanation. The techies will skim or skip the intro and go to the more technical sections below. --ChetvornoTALK 19:13, 5 May 2011 (UTC)
"Frequency is also a characteristic of waves" is true with a little stretching. And "It is used to describe the pitch of musical tones" is certainly true, since pitch is quantified as hertz. But "used to describe...the color of light" may be too much of a stretch, since color is not a one-dimensional thing like frequency, or like the simple conception of pitch. You often see confusions like "what is the wavelength (or frequency) of purple? of brown? etc." that we don't want to feed. Can we just leave out the bit about color? Dicklyon (talk) 00:38, 6 May 2011 (UTC)