Talk:A-weighting

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I've restored this page to it's proper meaning, moving content from Weighting filter which has also been restored to it's proper (more general) meaning. I've attempted to clarify the fact that this page is about A,B,C and D weighting, by refering to these early on, and explaining them more. I don't think it would be appropriate to call the page A,B,C and D weighting, as no one is likely to search for such a title! I have fixed the redirect pages for B-weighting etc to point here now rather than to weighting filter.

The important point is: although this page is about a family of weightings, it most certainly is not about 'weighting filters' in general, as they are not confined to the field of audio. Please do not merge again! --Lindosland 14:47, 15 September 2007 (UTC)

That picture of the ear seems to be totally unnecessarry, and a bit stupid, too. Csab 16:01, 12 October 2007 (UTC)

I disagree with Csab. It provides an opportunity for the caption text. Besides, the ear and hearing is what this is all about. Pzavon 01:53, 13 October 2007 (UTC)

Time to change name of this article[edit]

This article has been substantially changed in structure and contents over the last few months. As it now has sections dealing with the B, C, and D weightings as well as with A, it seems to me that a name change is needed. I suggest "Accoustic Weighting Networks" but would be delighted with something clearer and less technical if it were also reasonably descriptive of the article's contents. Any ideas? Pzavon 02:17, 8 November 2007 (UTC)

I strongly oppose such a change. What people will search for is 'A-weighting'. That is what is widely used, but since it forms part of a set their inclusion here is appropriate. The other weighting's in the set do not warrant their own page, in fact the whole set need to be seen in the context of each other. They therefore re-direct here. The title 'acoustic weighting networks is far too broad, as it includes many other weightings used in broadcast, acoustics and telephony. Some of these, like 468-weighting and phsophometric weighting already have full pages and links from here. --Lindosland (talk) 17:20, 21 November 2007 (UTC)

Then let's find another way to deal with this. If C-Weighting does not deserve its own article, neither does A-Weighting. If C-weighting can redirect here, then so can A-Weighting. THIS article is clearly no longer only about A-Weighting and needs a better, title that is more correctly descriptive of its contents. How about "Noise Measurement Weighting Networks"? Pzavon (talk) 02:47, 22 November 2007 (UTC)
This is simply not true. Many articles contain sections that could become articles in their own right, but they are kept as a unit because they are closely related, and hence benefit from a common introduction and other common material. The various weightings known as A,B,C,D share an important commonality - they are a related set of curves defined in a single international standard document. "Noise measurement weighting curves" is not a good title as it would have to include a lot more curves than the ones here. There is already an article on Noise weighting, which links to this and other curves (Psophometric, ITU-R 468 etc). A-weighting is a phrase that is referred to very frequently, being the only one of the set of curves in the standard described in this article that has achieved ubiquitous use in many areas. It therefore deserves to be the title of this page. 'A-frequency weighting' is a clumsy phrase that I have never seen or heard used - I will therefore revert it. --Lindosland (talk) 16:51, 7 April 2008 (UTC)
"The various weightings known as A,B,C,D share an important commonality - they are a related set of curves defined in a single international standard document. " That is precisely why the article should have a title that covers all of them. If you don't think "Noise measurement weighting curves" is an appropraite title, please suggest something else, because I'll me changing the title pretty soon. Pzavon (talk) 02:23, 8 April 2008 (UTC)
I can't understand what you think is gained by changing the title. An encyclopedia needs articles about things people are likely to want to look up. They are very likely to want to look up 'A-weighting' or 'A-weighted'. They are pretty unlikely to look up 'noise measurement weighting curves', and if they do then they are probably interested in all such curves, in which case this is not the best page for them - they want "noise weighting curves" which will show them the choice available, acting effectively as a disambiguation page. A more correct title for this page would be 'IEC61672:2003 noise weighting curves', but who's going to look that up? In any case, that title would not be correct, since that is only one of many standards that define the same curve, since these curves have been defined in many international standards in different countries (BS ISO ANSI etc). In fact the original standard that defined the curves is now obsolete. So, yes, you could go for 'Noise weightings A,B,C, D,E and Z as defined in IEC61672:2003 and other international standards'. Not very attractive though surely? The one thing that characterises all these standards, and which started them all off, and is quoted very widely indeed is 'A-weighting'. I hope you will understand this and leave the title alone. You could criticise many other articles as not strictly describing what they are about. Take Lamarckism which has a redirect from Neo-Lamarckism, or Industrial revolution which some have criticised as refering to a specificy western revolution. The latter is accepted because most people looking up the term will be using it as shorthand for 'the nineteenth century industrial revolution which began in Britain, and spread to the Western World.'--Lindosland (talk) 16:21, 9 April 2008 (UTC)
There will still be an article on A-weighting. It will be this one. There will still be an article titled A-weighting, which people will find in searches. It will just redirect here. I strongly support this move proposal. — Omegatron (talk) 01:43, 10 April 2008 (UTC)
No there won't be an article titled A-weighting, there will be a redirect of that title to this article under a name which I am suggesting will be highly innapropriate for the reasons I have given. The title 'Noise measurement weighting networks' is very bad for three reasons. Firstly, what do networks have to do with it? Yes, weighting can be done with networks, but it can also be done in DSP as pure calculation, and these days it is commonly done that way. Secondly, there are and have been many many noise weightings, and to try to explain everything about all of them, their history, their application and their specification on one page is to add confusion and limit future development. Thirdly, not all 'noise weighting' is about measurement. A-weighting is, and ITU-R 468 noise weighting is, and psophometric weighting is, but then there is noise weighting for noise shaping in digital audio. And not all noise weighting is about audio, as noise weighting can be used in video, and EMC measurement, and infrasound measurement, and radio astronomy - it's a big topic, and we have a page already on 'noise weighting' that acts as a disambiguation for the subject. Renaming this page, which is well established, would be a big change, and upset many wikilinks that would have to be changed. It should not be done on a consensus of two, especially as I have seen no reasoned answers to my objections. I hope to create articles about Zwicker, and more advanced weighting methods that have recently been described to cope with all levels and spectra by simulating human hearing. We will then have maybe six articles or more on different methods, all worthy of their own space. I suppose the only alternative title I would accept as properly describing this page is 'A, B, C, D and Z-weighting' but it's too cumbersome and problematic (do you include the commas or not? The dash?) It's not worth the hassle of all the changes to redirects and links. --Lindosland (talk) 10:09, 11 April 2008 (UTC)
Oh, and let's not forget the fundamental fact that this page is not even about NOISE weighting anyway! The A-weighting curve was invented for sound level measurement, and defined in a standard relating to sound level measurement. It is based on pure tone audiometry, not noise, and though it is now commonly used for noise measurement it is well known that it is not really suitable for that purpose. The other curves are not featured in all the standards, so the point about A-weighting is that it is the common feature in many standards and many applications, and the starting point historically. --Lindosland (talk) 10:19, 11 April 2008 (UTC)

Use of the gain functions[edit]

It remains completely unclear how the gain functions in the article are used. They are displayed as functions G(s). But what is s and what is its unit? The frequency (Hz)? Or any function of it (e.g. the wavelength or wave number)? Please clarify this because the reader cannot be expected to have expert knowledge.--SiriusB (talk) 22:56, 2 February 2008 (UTC)

I have added the weighting functions of the frequency for A, B and C from [1] (these are what most readers are probably looking for rather than for complex transfer functions), where one can guess how frequency weighting is related to those transfer functions. However, I do not have translated D into a weighting function yet since the formula is much more complicated and has to be tested before posting. Maybe I find time do to this, but perhaps someone else may add it from another source.--SiriusB (talk) 10:30, 27 February 2008 (UTC)
Update: I have added a formula from [2] that lists an algorithm for all four filters. It also contains a graph that is well reproduced by the formula (tested!). However, the resulting graph (as well as that shown in the paper) differs from that in the article for frequencies above about 10 kHz. Since I have found the same graph in several other sources, we should think about replacing the graph in the article by an updated one. Since I didn't find any tool so far that creates valid SVG images from a graph (maybe Gnuplot's SVGs are valid, but, however, are not properly displayed in any browser I have tested) may I ask the original author of the graphs to redraw the SVG with the new formula?
In addition, someone should validate the transfer function for D. I have tried to convert it into a weighting function (as far as I can see one has to calculate the absolute value of the complex coefficients where s=2i*pi*f is the imaginary part), but didn't get the correct function (but a function that looks similar to the graph). Maybe the D transfer function is wrong.--SiriusB (talk) 13:06, 28 February 2008 (UTC)

The Graphs are Correct[edit]

I drew the graphs in this article (and several others) very carefully, and I believe they are correct. When I decided to start manufacturing audio test equipment in 1978 (I founded Lindos Electronics) I was for a while misled by graphs that appeared in various publications that differed. This was particularly true of the CCIR-468 curve which people seemed to have their own variations on. So I obtained the standards and got to the truth. Please don't make the mistake of drawing graphs based on a poll of what is out there - much of what is out there is simply wrong because the standards are very expensive (and guarded from a copyright point of view) and so few people have them.

Almost all audio standards use weighting curves that are defined in terms of a table of values with tolerances. They do not concern themselves with the means of realisation. At first this surprised me, but it makes some sense. You build the filter how you like, and check it against the table. I would be interested to know where those equations came from in the article. As far as I am aware they are not from the standards, and so should be quoted only as 'a possible realisation' that meets the requirements laid down.

I've just pulled out BS6402 (Sound Exposure Meters) and it lists a neat table of values for A-weighting from 10Hz to 20000 Hz. This table occurs in many other standards. Looking at the higher frequencies it reads:

1250Hz +0.6 +/-1.5 1600 +1.0 +/-2.0 2000 +1.2 +/-2.0 2500 +1.3 +/-2.5 3150 +1.2 +/-2.5 4000 +1.0 +/-3.0 5000 +0.5 +/-3.5 6300 -0.1 +/-4.5 8000 -1.1 +/-5.0 10000 -2.5 no tolerance given 12500 -4.3 16000 -6.6 20000 -9.3

A note explains that since testing at the higher frequencies is not required no tolerance is given. So others may have their own way of realising these filters but it is the values in this table that are difinitive. I have realised weighting filters in many ways. A-weighting is easy and can be done with a purely R-C network without any second order sections. 468 weighting, with its 0.2dB tolerance at 6k3Hz is hard when repeatable manufacture is required, and I have used sections with zeros as well as poles to realise this simply with minimum sensitivity to component variation, without going to the 6-pole filter that is given as an example in that standard. If anyone can show that my graphs are wrong with reference to any STANDARD document, please quote the details.

I would add that as far as I am concerned the standards are innadequate, because they do not adequately reflect the rapid rolloff in our hearing around 20kHz and do not even specify any sort of falling response above 20kHz. It is therefore possible to make an A-weighting filter that complies with the standard but gives quite different readings from other filters that also comply when noise at 20k and above is present, even at quite low levels. The ITU-R 468 noise weighting filter is much better in this respect, with a high-order rolloff. I have made this point in many places and it is generally agreed that the A-D weightings should always be used with a steep low-pass filter around 20k for consistent results. I think the curves are overdue for replacement, especially now that we have revised Equal loudness contours standardised a few years ago. --Lindosland (talk) 10:37, 24 June 2008 (UTC)

Could you please repost the picture in a file format supported by Internet Explorer? .svg is not a natively supported image format and the pictures are all screwed up. This would be fine if I was the only one using IE, but such is not the case. The whole world is on IE and it would be nice if we could see the pictures. Thanks. —Preceding unsigned comment added by 66.216.131.162 (talk) 01:43, 16 January 2009 (UTC)

The graph is screwed up, but I usually don't have a problem with svg format (and I do use IE) so I think perhaps there was a problem in converting the graph to the svg format. It certainly needs fixing, but I don't think the choice of format is to blame. Pzavon (talk) 03:24, 16 January 2009 (UTC)
I'm not using IE and the graphs are a real trainwreck 80.171.39.211 (talk) 22:39, 8 February 2009 (UTC)
I've tried it on several browsers and the text by the axes is not formatted correctly. There are words on top of words. Is there any reason this can't be saved as a standard jpg or bitmap? 74.92.147.125 (talk) 20:56, 2 March 2009 (UTC)

At User:Lindosland: Do you know any method to extract the tabulated values of the data points out of an SVG image? My intention would be to create an interpolation table from these (or other) SVG graphs in Wikipedia. I recently found that Gnuplot 4.2+ seems to create valid SVGs and Opera/Firefox do correctly display them. Thus I started to re-create my graphs as SVG, and where it is possible I include the underlying formulas or even the Gnuplot script. However, I've never thought about extracting data from an SVG graph. Is there any way to do that automatically (i.e. not by just measuring the reference points by hand)?--SiriusB (talk) 19:29, 8 March 2009 (UTC)

Incorrect usage of A-weighting[edit]

There seems to be a lot of discussion in this article about how A-weighting curves are often used in situations in which they are not well-suited. There has to be at least 10 times where the author notes that A-weighting curves are often used, but the results are substandard because an ITU-R 468 curve or some other curve would have been so much better. However, very few of these somewhat controversial statements are backed up with a citation. Unless a reference to a published source can be produced, then these statements are only the opinion of the author. In any case, if A-weighting is truly an obsolete standard (according to valid published references), then I think it should be said once towards the top of the article. The rest of the article should deal with what A-weighting is, not all of the different ways in which it is commonly used in non-ideal situations. At this point, this article is more about ITU-R 468 than it is about A-weighting. Remember, this is an encyclopedia, not a technical blog. 74.92.147.125 (talk) 20:44, 2 March 2009 (UTC)

You make a good point. Perhaps you can do some editing. Pzavon (talk) 02:51, 4 March 2009 (UTC)
I was responsible for many of those 'opinions', some years ago, and if I were starting again now, after some years of Wikipedia experience, I might look harder for citations. However, I do stand by what I wrote, and it is not just my opinion - the problem is that since I have been involved in this topic professionally for over thirty years and know of no-one who has taken a deeper interest in it, much of what is written is by me. I was told early on that I cannot cite my own work, and removed many references in response to (quite properly made) objections. I did leave one reference to material in 'the Audio Engineers Reference book' which was written by me but is surely of high standing.
Might I suggest that one simple way out is for other editors to read my writings at:
http://www.lindos.co.uk/cgi-bin/FlexiData.cgi?SOURCE=Articles
http://www.lindos.co.uk/cgi-bin/FlexiData.cgi?SOURCE=Articles&VIEW=full&id=1
http://www.lindos.co.uk/cgi-bin/FlexiData.cgi?SOURCE=Articles&VIEW=full&id=2
http://www.lindos.co.uk/cgi-bin/FlexiData.cgi?SOURCE=Articles&VIEW=full&id=10
and put in links and citations as appropriate. You can do this, but under Wikipedia rules I cannot!! I think they represent some of the best information available, and Lindos electronics is a well-respected and very well known manufacturer of audio measuring equipment with a long involvement especially in broadcasting where noise measurement has an important history.
I do not think I have suggested that A-weighting is 'obsolete'. As a standard it certainly is not, but it is a fact that it is widely seen as having severe weaknesses and limitations, especially when it is used widely for purposes for which it was not originally intended, and I don't think it is out of place to make those knnown limitations clear here. --Lindosland (talk) 12:17, 20 March 2009 (UTC)
A-weighting is a curve defined in various standards documents. Because of its long history there are many relevant standards, some out of date, but as far as I am aware the specification is in the form of a table, not an equation. The equations given in the article appear to be from a web article, and I suspect they have been devised by someone in relation to a specific filter realisation rather than coming from standards. They may be useful to include, but unless someone can cite their source in a standard I think it should be made clear that they are 'unofficial'. Most standards define weightings in terms of tabulated values at set frequencies with tolerance limits at each frequency, leaving the method of implementation open to the designer. There is not one filter realisation that meets the specification, but many. --Lindosland (talk) 14:29, 20 March 2009 (UTC)


Sounds like someone has an axe to grind (or a product to sell?) A-weighting is used by a lot of people, and I don't really think the dismissive tone of this article is appropriate. It probably wouldn't read like this if it we're dominated by the contributions of a single person. —Preceding unsigned comment added by 71.167.62.224 (talk) 01:03, 16 July 2009 (UTC)

Original research[edit]

Though the noise level of 16-bit audio systems (such as CD players) is commonly quoted (on the basis of calculations that take no account of subjective effect[original research?]) as −98 dBFS

This is not OR. The figure is calculated directly from the bitwidth, as explained in DBFS#Dynamic range. 95.222.120.117 (talk) 12:59, 29 May 2009 (UTC)

That says nothing about "subjective effect". —Preceding unsigned comment added by 71.167.66.107 (talk) 21:19, 14 July 2010 (UTC)

dBrn - too funny![edit]

One of my greatest pet peeves in information technology is the unbelieveably broad range of exceptionally poor proportional fonts that exist - as well as the propensity for individuals (like Wikipedia) to choose really bad ones. Wikipedia, for example, chooses a font for article titles in which the capital "i" and the lower-case "l" are completely indistinguishable. So, for instance, the ILyushin IL-2x aircraft all have pages on Wikipedia titled "llyushin ll-2x" as far as the reader can tell. Another annoyance is that a significant number of proportional fonts (including the body text font selected for Wikipedia pages) make it *almost* impossible to discern the difference between the lower-case letter "m" and the pair of lower case letters "rn". So imagine the humor when upon close inspection I confirmed that in place of the phrase "dBm adjusted" on this page the phrase "dBrn adjusted" appears! And how much more humorous it became when I realized that this had been read for months if not years unnoticed by any number of people. Please fix. --65.202.227.148 (talk) 21:34, 16 December 2009 (UTC)mjd

It is unfortunate that they look so similar, but dB(r n) is a real unit and it is different than dBm. See dBrn page for details. --Aandroyd (talk) 17:13, 28 December 2010 (UTC)

Is the Animation/Video really necessary[edit]

For the image titled: "Video illustrating A-weighting by analyzing a sine sweep," is an animation really necessary? I do not see any insight gained by having an animation versus a static image. Anyone agree? —Preceding unsigned comment added by MaverickPS (talkcontribs) 08:41, 18 July 2010 (UTC)

I added the animation a while ago and think it is a useful contribution, but if you disagree by all means remove it and replace it with something better. Please note that the video contains audio (the sine sweep), you may have missed that and without the sound the animation is indeed meaningless... --Mikael Ogren (talk) 12:39, 17 August 2010 (UTC)

Distance[edit]

That 1 metre or 3 feet is used is verified here: http://www.comairrotron.com/acoustic_data_comparison.shtml but I don't know if it is allowed to insert a link to a manufacturer's site. Says "In our industry, this distance is typically either three feet or one meter.". Definitely better to have this source in the talk page than none at all. —Preceding unsigned comment added by 217.209.36.180 (talk) 05:45, 8 December 2010 (UTC)

Dead link[edit]

During several automated bot runs the following external link was found to be unavailable. Please check if the link is in fact down and fix or remove it in that case!

--JeffGBot (talk) 22:06, 19 June 2011 (UTC)

Errors in the transfer functions for A-weighting[edit]

The original reference [6] in A-weighting should be http://www.ptpart.co.uk/noise-measurement-briefing/. The imaginary unit i in the poles within the section A-weighting#Transfer function equivalent is wrong. (See the original reference http://www.ptpart.co.uk/noise-measurement-briefing/.) TZawada (talk) 10:21, 17 April 2013 (UTC)