Talk:Band-pass filter

Untitled
Tihe page history for this article has been merged from three articles on the same topic. It probably doesn't make a lot of sense now. Please could someone who understands the content of it merge the three in properly. Thanks. Angela 02:42, Sep 28, 2003 (UTC)

The article says that a band pass filter is USUALLY, if we are not going to spell out exceptions we should remove that qualificiation.

Discard "Gibbs phenomenon" reference
The rippling in the frequency response of a filter has ABSOLUTELY nothing to do with the Gibbs phenomenon (the so-called "overshoot" response in the time domain to a filtered step function). The "ripples" in the frequency domain for some filters (e.g. Chebyshev filters) are a design choice, unlike the "Gibbs phenomenon" which is unavoidable mathematically.... Aargh. 90.17.171.36 14:41, 15 June 2007 (UTC)Gerard

Thanks to whoever fixed the article to remove that unfortunate analogy with the "Gibbs phenomenon". 90.23.13.141 15:02, 10 July 2007 (UTC) Gerard

The example;
What order of filter is the example in the article? -- &infin;Wirelain 03:56, 10 July 2006 (UTC)

Not all bandpass filters have a bell shape. scoofy 20:13, 7 April 2007 (UTC)


 * True, and the word "bell" is nowhere in the article. But I agree the example figure is misleading and atypical, and the caption is complete nonsense. Dicklyon 01:16, 8 April 2007 (UTC)

^^ are you kidding? Obviously you have no idea what a bode plot is. The graph should contain a logarithmic frequency axis. I agree the graph is misleading in its bell shape, however, the caption clearly states that is only symbolic. The actual graph would have much sharper corners at both the high and low cutoff frequencies, however, as a simple, symbolic graph it is more than adequate. —The preceding unsigned comment was added by 137.104.249.250 (talk • contribs).


 * I don't see any indication that it should be a Bode plot. But as I said, it's misleading and atypical, and therefore really NOT "more than adequate". It's particularly inadequate if it gives wrong impressions. Dicklyon 21:22, 25 April 2007 (UTC)


 * The plot has been replaced with one that is less bell shaped and more bandpass shaped. It is not a Bode plot.  The ordinate is linear, and the abscissa is unspecified. Dicklyon 07:17, 28 June 2007 (UTC)


 * Square shaped bandpass can be obtained by using crystal filters —Preceding unsigned comment added by 193.71.218.226 (talk) 11:21, 9 April 2010 (UTC)
 * No filter class can produce square filtering - only close approximations to it.  Sp in ni ng  Spark  11:51, 9 April 2010 (UTC)

Wah Wah
Since Wah pedals are probably the most famous implementation of a Bandpass filter; shouldn't they be mentioned? —Preceding unsigned comment added by 143.239.7.1 (talk) 15:48, 27 October 2007 (UTC)


 * Sure they should; but not without a source. Dicklyon 17:05, 27 October 2007 (UTC)
 * The wah-wah pedal is a bandpass filter with that is also tunable. "Most famous" is nonsense except among a few electric guitarists and must not be claimed in the article. Cuddlyable3 (talk) 09:28, 2 August 2011 (UTC)

Bandpass Formulas
I see that other filter pages have formulas. Why doesn't this one. I was looking to see if the formula for the center frequency uses the one I discovered in the early 80's. I have not seen it anywhere, yet. The formula is Fo=√FlFh (sorry, new to wiki don't know how to make sqrt look correct). ClydeCoulter (talk) 05:58, 1 October 2009 (UTC)
 * $$\textstyle \sqrt {f_1 f_2} $$ is the formula for the geometric mean of the two end frequencies. Center frequency more usually means the arithmetic mean $$\textstyle \frac{f_1 + f_2}{2}$$. Both of these, in general, will be different from the resonant frequency of the resonators which depend on filter design.  Sp in ni  ng  Spark  06:42, 1 October 2009 (UTC)
 * $$\textstyle \sqrt {f_1 f_2} $$ is the logorithmic center which does apply to a simple bandpass filter. The older usage of calculating the center frequency using $$\textstyle \frac{f_1 + f_2}{2}$$ is way off in the audio range of frequencies.  This could be discussed on the bandpass page with examples. (thanks for the example of markup for these formulas) ClydeCoulter (talk) 11:04, 1 October 2009 (UTC)
 * It depends on your application. FM for instance, is usually aiming for a linear deviation of the carrier, arithmetic mean is the most applicable concept.  In audio you are probably looking for the centre-frequency which has an equal number of octaves either side; that would be the geometric mean.  There are many other possibilities for mean.  Sp in ni  ng  Spark  20:43, 3 April 2010 (UTC)


 * Yes, someone, I guess me, ought to put up the formula in terms of the convolution with the sinc function. It is used in textbooks like all the time.200.55.128.88 (talk) 18:22, 5 November 2014 (UTC)

Erroneous use of Kilroy
Hey all, as can be seen on the RLC circuit page, http://en.wikipedia.org/wiki/RLC_circuit, Kilroy is actually a band-STOP filter. Is Pynchon wrong, or was this added to the wrong page by mistake? I'm removing the Kilroy reference until it can be decided, as it could lead to confusion w.r.t the circuit.


 * Yes, it looks like Pynchon was in error, unless that circuit fragment was used in a shunt leg. But check the ref to V; it's on the right page.  We can still use it, as long as we attribute what he said, rather than repeating the error as fact.  So I fixed it.  Dicklyon (talk) 06:18, 29 May 2010 (UTC)


 * Perhaps he meant to say "Kilroy stopped here".  Sp in ni ng  Spark  11:49, 29 May 2010 (UTC)

Kilroy Reference Irrelevant
Can someone please remove this reference from the article. It is completely irrelevant and only serves to create confusion. This article is scientific in nature and "fun factoids" and pop-culture trivia of this nature have no place. Do we see subsections about flux capacitors and the movie Back to the Future in the capacitor or memristor articles?

Not only is the circuit drawn in a non standard way, with curved connections, it also misrepresents what the article says it is, rather than giving a disclaimer that it is not a true bandpass filter. The curved connections and drawing of the circuit also look too much like the actual bode plot of the filter, which also creates confusion. When researching for my thesis, I came upon this article and now I'm quite annoyed that this is the first time a Wikipedia has really come off to me as unprofessional and unreliable. Please keep to the standards and the owner of this section or someone who is comfortable with editing the article should delete it. --Doornatab (talk) 16:45, 8 May 2011 (UTC)
 * I agree with you, and removed the section. The item is still mentioned at Kilroy was here which is reasonable, but the erroneous claim (however well verified in a novel) is not relevant to an understanding of this topic, and is not helpful to this article. Johnuniq (talk) 03:36, 9 May 2011 (UTC)


 * I can see that it might be "unhelpful", but not irrelevant. The relevance is that Pychon described the schematic as a bandpass filter.  There's a reliable secondary source in addition to the appearance in the novel.  How does it create confusion?  Removing it just because you (Doornatab) see it as unprofessional is not provided for in policy or guidelines that I know of, and it's not clear what you mean by unreliable here.  There are no owners here, so anyone can remove it, but more supportable reason would be needed, I think.  So I reverted the removal.  Dicklyon (talk) 05:20, 9 May 2011 (UTC)
 * Are you suggesting there is some merit to the claim that the Kilroy was here image arose from a circuit diagram? Or, do you think it is an obviously wrong but harmless anecdote to enliven the article? It appears that Pynchon's only comment about Kilroy was a very short sentence in a novel—not even an assertion of truth, but a passing thought that the author may or may not have believed. What is certain is that the diagram is not a band-pass filter, and if there were some encyclopedic reason to keep the anecdote, a sentence would need to be added explaining that Pynchon was wrong, and that the diagram does not portray a BPF. Also, articles do not include every verifiable factoid—there needs to be a reason to include the material. Johnuniq (talk) 07:38, 9 May 2011 (UTC)


 * How is an anecdotal reference to a bandpass filter from a non-credible source of electronics/science (its in a novel, not a scientific work or text) relevant to information about bandpass filters? If we take all anecdotal references to a particular subject, the focus of the article is lost.  With this particular article being so small, with only 3 figures, one of which is not even a bandpass filter related figure, this subsection removes focus from what a bandpass filter is.  I also have to agree with Johnuniq that this subject is much more appropriate in the Kilroy was here article, so why can't it be mentioned there only?  If it is so important that people know that you can draw a circuit to look like "Kilroy was here", can you not just put a link to the "Kilroy was here" article in the see also section?  Also, please address the fact that the schematic is not representative of what the article is about.  With the way the subsection is written and the caption of the figure, using Pynchon as a source, it is actually calling the figure a bandpass filter.  Any reader who has little knowledge on electronics, filters, or who Pynchon is and what this novel he wrote is about, can easily be misled by this.--Doornatab (talk) 12:18, 9 May 2011 (UTC)


 * No, I'm not suggesting that there's merit to the claim. I also don't think it's obviously wrong.  But these opinions don't matter.  As to whether the circuit is a bandpass filter, that depends entirely on where you put an input and where you take an output; and it really doesn't matter.  Without a source to that effect, there's no reason to say that Pynchon was wrong.  There is a reason to include it, which is that it is a reference in popular culture that has been commented on in a reliable secondary source.  I'm not in favor of the proliferation of pop culture items that are either unsupported or supported only by a primary reference, but this one is one of those rare legitimate ones, on topic, and verifiable in a reliable secondary source.  Notice that our text does not say that it's a bandpass filter, only that Pynchon said it was; I don't see why you've been misled to think otherwise.  Dicklyon (talk) 15:05, 9 May 2011 (UTC)
 * Going meta on this for a moment, there's a good reason to have such a popular references section. It estabishes a certain standard that makes it much easier to defend against the more common popular references crap that tends to accumulate.  It's easy to point to it and say, see, this one is from a secondary source, your new addition is not, so out it goes.  Also, if you take this out, I guarantee that you'll see it reappear repeatedly, but without the citation to the secondary source, so you'll create an ongoing maintenance problem.  The way it is has been stable, due to the sourcing.  Dicklyon (talk) 15:08, 9 May 2011 (UTC)

I am neutral on whether to keep this or not, but I just have to comment that all this criticism of the technical accuracy of the Kilroy circuit is rather silly: it is not meant to be a real circuit that actually works for goodness sake. By the way, when I took my graduate exams (admittedly a long time ago - sometime in the bronze age right after they invented copper wire) rounded corners on circuit diagrams were not only not wrong, but were a requirement.  Sp in ni ng  Spark  18:21, 9 May 2011 (UTC)
 * So then why show a circuit diagram if it is not meant to work? When I go to the bandpass filter article, am I going there to read about bandpass filters or am I going there to read about some trivial reference with inaccurate schematics? I find this subsection is biased in that the author finds it humorous or special for knowing the reference; it adds no value to the article while at the same time misleads the reader in understanding what a bandpass filter is.  Let me put it this way, I saw the diagram and saw the caption that some person "Pynchon" declares it to be a bandpass filter.  I immediately didn't recognize how it could be a bandpass filter, but I don't work with analog filters every day, and so I actually had to study this "Kilroy was here" diagram for a minute to make sense of it and to verify to myself that it was not even a bandpass filter.  I was only to realize that it was, for lack of a better term, a "geek" reference.  Should Wikipedia users expect to question and invalidate the information provided on every article?  I thought this was the kind of stigma that people wish to remove from Wikipedia.  Talk about misleading and a waste of time.--Doornatab (talk) 19:11, 9 May 2011 (UTC)


 * @Dicklyon ...As to whether the circuit is a bandpass filter...:
 * This article is about band-pass filters, so of course it matters what information is displayed. I understand what you're saying about where you put an input, but in this case the diagram cannot be a BPF in any configuration (without additional components), and the diagram (while not intended to be taken seriously) is drawn in a manner that demands the conventional interpretation (input at left, output at right, common incorrectly omitted). The claim that without a source there is no reason to say that Pynchon was wrong is hard to follow as the corollary would be that any nonsense in a novel can be added as a factoid to any article provided no reliable source has contradicted the particular statement. I see that even the article on the book includes the unsourced "Technically, a band-stop filter", so it is more accurate than this BPF article!
 * ...reference in popular culture that has been commented on in a reliable secondary source...:
 * That is not correct. The source is a literary critique ("this study analyzes Pynchon's fiction in terms of its radical dimension, showing how it points to new directions in the relationship between the political and the aesthetic"), and completely fails WP:RS for any comment regarding (1) band-pass filters, or (2) the origin of "Kilroy was here". The source simply quotes and comments on Pynchon's reference to Kilroy. The source does justify including information on Pynchon in Kilroy was here.
 * ...if you take this out, I guarantee that you'll see it reappear repeatedly...:
 * I have some sympathy for this approach, but of course it is totally wrong: we don't insert undue conspiracy theory nonsense into articles on politicians on the basis that removal will cause it to "reappear repeatedly".
 * Reasons to remove the Pynchon material include that it does not assist any understanding of the topic of this article; the diagram would mislead or puzzle many readers who actually wanted information on BPFs, because it is not a BPF; the material trivializes the topic. Are there any reasons to include the material? Johnuniq (talk) 02:58, 10 May 2011 (UTC)


 * I don't see the problem. Neither our article nor the cited secondary source makes any claim that that is a bandpass filter, nor that it is the origin of the Kilroy.  They merely report that Pynchon said that in his novel, a work of fiction.  I don't think there are any questionable statements here.  Furthermore, that circuit absolutely can be a bandpass filter; put the input across the far ends (differential input through the resistors) and take the output across the parallel tank circuit (differentially again).  Do I think that's what he meant?  No, not really; I think he invented a story about a fragment of a circuit.  So what?  And have I read the book?  No, I  haven't; but I've look at the picture.  Dicklyon (talk) 03:14, 10 May 2011 (UTC)
 * OK, I just noticed a problem there; I don't actually have, nor have I seen, the cited secondary source; but the primary source disagrees with our caption, because it says Kilroy came from a "part of a bandpass filter". I've updated the caption to reflect that, which may make it less objectionable to you.  Also I found another source: ; this one, however, makes a claim that is very questionable, that Kilroy came from a BPF schematic, and cites Pynchon's fiction as the source; so I would definitely agree that it should not be treated as a reliable source.  Dicklyon (talk) 03:22, 10 May 2011 (UTC)
 * I see the debate above about the accuracy of this quote about Kilroy. As others have said it misses the point. It has no place in a serious article on an important concept. Especially in an article that is so thin on detail anyway. Can we just remove it now? Billlion (talk) 13:30, 4 January 2013 (UTC)

SQRT(2)/2 is not -3 dB
I am referring to the drawing of the bandpass filter at the beginning of the article. SQRT(2)/2 = .707. -3 dB = 1/2. This can be verified by doing the math. I think some clarification is required. Stewartm001 (talk) 15:34, 22 December 2011 (UTC) Mike


 * The 0.707 is amplitude, corresponding to 0.5 power ratio, or almost exactly -3 dB. Dicklyon (talk) 18:21, 22 December 2011 (UTC)
 * Amended to 3.01 dB in the article to give a cue that this is not inherently an integer. (It can be calculated as ten times the base-ten logarithm of 0.5.)
 * —DIV (1.145.54.45 (talk) 05:07, 30 November 2022 (UTC))
 * Oops. I got mixed up.  Actually I made that amendment in the Passband article.  The same amendment could also be made in this article.  —DIV (1.145.54.45 (talk) 05:10, 30 November 2022 (UTC))
 * 3.01 is no more exact than 3 so I don't see the point of this Spock-like over-exactness. The difference amounts to only about a quarter percent of the power level.  That is of no significance to engineers in the field and possibly not even measurable with the equipment available.  Of course, this would be significant and measurable in a standards laboratory or some esoteric research, but such applications would hardly be expected to be using engineers' clumsy decibel representation. SpinningSpark 09:22, 30 November 2022 (UTC)
 * Why are you repeatedly adding a diatribe about blocking policy to your posts and edit summaries? Is this some kind of trolling? SpinningSpark 09:22, 30 November 2022 (UTC)
 * Agree. 1.145.54.45, this is not the place to lobby for changes to policy. Deleted it. --ChetvornoTALK 17:10, 30 November 2022 (UTC)

Recent edits to examples
It seems to me the ungrammatical and uninformative "Optical band-pass filters are of common usage." doesn't belong at the top of the Description section. An optical filter might be a good introductory example in addition to the tuned circuit to explain bandpass filtering to general readers; a colored filter allows a restricted band of light frequencies from a white light source through, resulting in colored light. But more needs to be said than the above. -- Chetvorno TALK 21:49, 17 May 2014 (UTC)


 * I agree with that, and I think Billion does too, he just has not looked at the result of his own edit. His first edit here moved that phrase down. He seems to be under the (completely wrong) impression that I put it back and reverted me.  What he has actually done, is not only restore the original problem but also create a new one by conflating optical filters with a description of very long period filters used on weather data.
 * My edits actually fixed both problems and also gave a better description of optical filters. As he has stopped responding on his talk page, I am just going to revert him.  Hopefully, if he has another problem we haven't seen he will respond here.  Spinning  Spark  00:32, 18 May 2014 (UTC)
 * It is much better now and sorry for the edit confusion. It is interesting that the interpretation of band pass filters in optics is "filters" in the traditional sense of coloured partially transparent media. It is quite right but I was thinking of band pass filters in photonics that have more in common with filters in analogue electronics and DSP in the way they are designed. I have seen such things in a lab, and helped people who model them mathematically, but I don't know how widespread their use is, for example in IR for communication. I suspect quite common now and maybe worth a mention? Here is an example from the literature http://ieeexplore.ieee.org/xpl/articleDetails.jsp?reload=true&arnumber=1161607. Billlion (talk) 07:44, 18 May 2014 (UTC)
 * You are more than welcome to add something. I think it is fairly safe to assume these are notable now, they are finding their way into texttbooks.  This one is in its second edition.  I would be cautious about saying that they are actually in practical use.  I am retired now and too out of touch to know, and all the sources I've looked at talk about the benefits they could have rather than do have.  Spinning  Spark  08:12, 18 May 2014 (UTC)
 * Just to add my two cents: I'd like to see a better basic explanation for general readers. The article should explain what a "filter" is, the transfer function, that bandpass filters are used in electronics, acoustics, optics, and digital filters, and contrast the bandpass with the lowpass and highpass.  Bandpass filters in electronics, acoustics, and optics are used for two basic purposes; picking out a frequency or frequencies from a composite signal, and generating a signal at a specific frequency in oscillators.   The one-sentence introduction does not comply with WP:LEAD as a summary of the article.  I think the photonic filter and the example of computer filtering of weather data give a rather WP:UNDUE emphasis on these technologies.  Before these examples I'd like to see more common examples, such as the ubiquitous IF filter in receivers, crystal filters, active filters in audio graphic equalizers, the phase-locked loop, the microwave cavity, dielectric resonator, and dichroic filter.  Acoustic resonators are bandpass filters that generate the tones in musical instruments.  -- Chetvorno TALK 12:25, 18 May 2014 (UTC)

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