Talk:FM broadcasting

message: This article used to have a lot of US-specific material.  To fix that, the original article was moved (along with its history) to FM broadcasting in the USA, then the non-US specific material was restored here. Therefore much of the editing history is now at the new article. --Tony Sidaway|Talk 23:32, 14 Mar 2005 (UTC)
replies: text:  January_5 FM radio is demonstrated to the FCC for the first time -- So. WHERE is the story? See also: frequency modulation and FM band there is NO INFO there!  85.197.25.108 (talk) 22:01, 1 September 2009 (UTC)
thread_title: History

message: I've linked to a number of terms (mostly used in the first paragraph after the introduction) which are technical jargon and undefined in the article. Some of those links probably don't go where they should. 
I know a fair amount about radio, certainly well beyond what the average person knows, and I find major portions of this article fairly incomprehensible. It was obviously written by someone who knows the subject and is used to communicating with engineers, not with nonspecialists. Because of this and the undefined terms, I nearly slapped a "clarity" tag on the page. But maybe I'm just having a bad day. In any case, I suspect this article reads like a lot of the mathematics articles here - mostly obscure to those outside the high priesthood. --24.237.89.66 15:00, 6 January 2006 (UTC)
thread_title: Definition of terms, clarity

message: Can anyone explain why 19 KHz was chosen as the pilot tone frequency for FM stereo and why it is necessary to have a such a wide (4KHz) guardband around the pilot tone. Surely a higher pilot tone frequency and/or a tighter guardband spec could be used to improve the audio bandwith beyond the 15KHz limit ?
Also I have heard there were/are rival systems to the Zenith/GE system. Does anyone know how these worked when/where the were/are used and how well they worked ?—Preceding unsigned comment added by 87.113.88.39 (talk) 19:32, 22 July 2006 (UTC)
thread_title: Zenith/GE system Pilot tone system

message: Basic stuff about frequency modulation, that is not specific to FM broadcasting, surely belongs in the article about frequency modulation. It should not be duplicated here. This article should describe FM as applied to broadcasting, and not FM in general, IMHO. Therefore basic stuff about wide versus narrow FM, Carson's rule, etc., belongs there. Harumphy 15:49, 23 July 2006 (UTC)
thread_title: Basic concepts

message: The wide versus narrow thing is  too simplistic, because in practice there is a wide variety of systems using a whole range of parameters which do not fit into narrow and wide camps. Where is the boundary between narrow and wide? How many kHz? Is an outside broadcast link, using 10 kHz peak deviation in a 50 kHz channel assignment to carry about 12 kHz of audio bandwidth wide or narrow? It may make more sense to talk of the modulation index, but again this belongs in the general FM article, not the FM broadcasting one. Harumphy 15:49, 23 July 2006 (UTC)
thread_title: Wide and narrow

message: Why is 87-108 (roughly) used for civilian FM broadcast? Who chose these frequencies? --81.105.251.160 01:53, 6 August 2006 (UTC)
thread_title:  Why 87-108 

message: This article is focused on "FM Broadcasting", and, largely the technical details of the science. I propose that the section entitled "non-broadcast uses" be moved to its own article or deleted. In truth, there are many other uses of frequency-modulated RF carriers than broadcasting. Wireless two-way communication, amateur radio, and occasionally data communications (though FM is an inefficient use of spectrum for packet-type radio). It may be of more use to have a section under "[Frequency Modulation]" on "application" rather than a "non-broadcast" section under the "broadcasting" article.--Gdickinson 02:08, 12 August 2006 (UTC)
thread_title:  Why "Non-Broadcast Uses?" 

message: The article states:
Stereo FM signals are far more susceptible to noise and multipath distortion than mono FM signals. This is due to several factors, including the following:
the addition of the two sidebands of the difference subcarrier to the baseband signal increases the noise bandwidth of the signal by a factor of three (9.5 dB) as compared with a mono signal. 
as mentioned above, the pre-emphasis is applied to the audio signals before encoding. This results in the pre-emphasis acting in the wrong direction on the lower sideband of the difference subcarrier, i.e. decreasing the level as the frequency rises, which will have a further deleterious effect on the S/N of the difference signal. 
*This is quite obviously completely incorrect.
:The pilot tone is 10 percent, leaving 90 percent available for information. That is a -0.915150 dB reduction in available information (signal) over monophonic operation. Further, on the average, fifty percent of this information is in the subchannel, that's an additional -6.020600 dB reduction in information. The sum of these two shows the reduction of the available S/N over a mono signal is -6.935750 dB.
*Then, the argument of the 23 kHz to 53 kHz information having pre-emphasis in the wrong direction is further incorrect. This information in the subchannel cannot be broken up in such an illogical way. The subchannel contains a pair of sidebands, with the originating carrier suppressed at least 40 dB. This L-R information exists in both sidebands. They exists in a phase-linear, flat-frequency-response portion of the supersonic audio spectrum. Guessing that baseband preemphasis somehow affected this is not supported by mathematics or information theory. At one time in the United States, there were three FM Stereo generators available, that compiled with the FCC Rules and Regulations. All three were designed by me. The January, 1974 Broadcast Engineering magazine, on page 25 starts a three-page article that I wrote as an expert. --LymanSchool 03:41, 28 December 2006 (UTC)
replies: text: It probably isn't all that helpful to argue about the S/N disadvantage of stereo signals, because there are so many variables that would need to be defined first. First, are we talking about S/N in the M channel, the S channel, or each or the L & R channels? Is the pre-emphasis 50 or 75 uS? Are we talking about unweighted or weighted noise? If the latter, A-weighted RMS, ITU-R 468 or something else? I suggest we should identify the sources of stereo noise without quantifying them. Harumphy 12:19, 28 December 2006 (UTC)

text: I believe the idea is that adding noise to the FM signal has an unusual relationship to the sidebands, and so to the decoded signal. But there is another way to look at the FM stereo signal, which shows that there is no such change. You can consider it as alternating between L and R at 38kHz. Added noise will add equally to the two channels, and deemphasis will then be applied. Gah4 (talk) 01:24, 6 December 2015 (UTC)
replies: text: Also, there is the Capture effect which reduces or eliminates noise due to weaker signals at the same frequency.  This is more than just the bandwidth increase, though that helps, too. Gah4 (talk) 23:55, 19 February 2017 (UTC)
replies: text: Well there is another consideration, that noise makes it harder to extract the pilot signal.  For one, that causes receiver to switch in and out of stereo mode.  Gah4 (talk) 22:16, 8 November 2018 (UTC)
thread_title: Wrong technical information about FM Stereo

message: I added a small section about ITU conferences; don't you think we should expand that section? I can do it, if we think we could do it. [Hamlet 26 Mar 2007]—Preceding unsigned comment added by 87.9.44.55 (talk) 21:57, 26 March 2007 (UTC)
thread_title:  Conferences about FM 

message: Would it be out of line to mention some commercial things under Small-scale use of the FM broadcast band? Specifically, Mr. Microphone under FM radio microphones and the Ramsey series of FM transmitter kits either under Microbroadcasting or pirate radio? I think they are both notable, but the Ramsey link in particular might be against WP:EL or WP:SPAM.--Mdwyer 20:27, 26 April 2007 (UTC)
thread_title:  Commercial References 

message: "A new device named IM cancelled high frequency clipper is able to give a heavy audio clipping at high audio frequencies with low ear annoying."
English, please!  --24.170.176.52 11:14, 29 July 2007 (UTC)
thread_title:  Um, what? 

message: IMHO it would be worthwhile to add an extra paragraph comparing FM quality (example: 50-16000 Hz, 60 db S/N) to AM quality (50-10000 Hz) and CD quality (20-20000 Hz) audio.   I actually came here hoping to find that information, and was surprised to see it's not listed, since the opening paragraph labels FM as "hi-fidelity".  Is it?  I don't see any numbers to back it up.  Thanks.  -  Theaveng 16:48, 27 September 2007 (UTC)
replies: text: By itself, there's nothing to say that FM is higher or lower fidelity than AM, SSB, or what-have-you. It all depends on the S/N ratio and bandwidth of the channel (so, for FM, the modulation index). While it's true that broadcast FM has lots more baseband bandwidth and fidelity than broadcast medium wave AM, that's more a function of the channel bandwidth consumed than the fact that the modulation is FM. Perhaps no one has been willing to write the explanation yet. Feel bold?  - Atlant 23:32, 27 September 2007 (UTC)
replies: text: This article is not about "FM" in general, but specifically about the FM Broadcasting technology, and thus can be stated to have a certain measurable sound quality for the ~200 kilohertz wide channels used in Europe and the U.S., versus the ~10 kilohertz wide channels for E.U. or U.S. AM radio.  -  Theaveng 12:22, 21 October 2007 (UTC)

text: I, too, came seeking numerical data on the nominal fidelity of FM audio broadcasting, especially for comparison to other (not necessarily RF broadcast) transmission methods, for an SDR project. Perhaps, what's needed are separate articles; one for the technical (implementation) aspects, and others for the cultural and historical significance, else a basic overview article which then points to more specific sub-articles like is done for other large and/or complex topics. — Lee Carré (talk) 14:37, 15 May 2019 (UTC)
replies: text: I don't think you will ever find any valid numerical data or anything else definitive about the audio quality of FM broadcast.  Audio quality is highly subjective.  What I think sounds great may mean nothing to someone else.  Compare it with vinyl records/CD recordings.  You could easily produce technical data that shows CD is better than vinyl, but many people will not accept it.  Hence the current resurgence of vinyl.Davidbstanley (talk) 17:54, 15 May 2019 (UTC)
replies: text: The assumptions on which your response seems based, are false, as relating to the intent behind my previous. Metrics such as SNR, dynamic-range (or equivalent bit-depth), frequency response, THD, and so on, are quite objective. I won't become ensnared by the ‘CD versus vinyl’ pseudo-debate, either. Part of the ‘resurgence of vinyl’ is actually because of the so-called Loudness War, but that's rather a problem with mastering rather than the specific format in question; CDs offer greater dynamic range than vinyl, due to physics. The same audiophools who claim that vinyl is superior to CDs in fidelity (regardless of their preference for listening source) tend, in my experience, to also claim that vacuum-tubes are superior to transistors. I have a fair bit of experience with audio tech, including having worked (for pay) as an AV engineer. By your argument, the ‘quality’ (though, I didn't use that word; I specifically chose “fidelity”) difference between a band-limited (often highly compressed) voice channel (such as is featured commonly within the PSTN) versus a lossless/raw source input (eg from a microphone into a preamp) is purely ‘subjective’. Nonsense. For example, during setup for a gig, it was permissible to play CDs over the audio system, but not audio-broadcasts (via any modulation), because even FM would make the audio system sound crappy compared to playing a CD (or equivalent/better, these days). Compare the equivalent absurdity of claiming that the fidelity of 240i versus 1080p is entirely ‘subjective’. I say that, even allowing for cases where greatest fidelity isn't the priority; if 240p is adequate, then I'll take the reduction in byte-count over the excess fidelity. The professional audio world (eg live gigs, recording studios) pays no attention to the opinions put forth by uninformed audiophools; the latter is oft regarded as laughably clueless. Learn from Monty of Xiph: Digital Media Primer. The very reason why FM became popular, for audio-broadcast, was its clearly superior fidelity compared to AM. — Lee Carré (talk) 01:26, 1 June 2019 (UTC)
thread_title: Addition: FM Audio Quality comparison

message: Removed clearly unencyclopaedic references to research by Oscar Bonello that don't enhance the overall article. He may well have important work, but unless it is referenced by wider works on radio, it's promotion here is inappropriate. Martyvis (talk) 10:11, 11 March 2008 (UTC)
thread_title:  Removal: Oscar Bonello research promotion 

message: The particular point of view of Mr Martyvis is dangerous for the Science. If every time a researcher shows the results of a published investigation ( accepted for the reviewers of the Journal) we  say "Discard it because Newton is promoting the Gravity Laws" probably the Science Books will be only blank pages...
As Mr Theaveng said, above this lines; " This article is not about "FM" in general, but specifically about the FM Broadcasting technology"  Then, there are two main questions to solve
1) How we can use pre-enphasis with music of high sound density above 5 KHz (like a CD recording) instead of the sound material used by Armnstrong in 1933 ?  We indicate where to find this answer
2) Yet more complex (and frequently asked by my pupils at University) Why a signal that has ever the same power (in FM the amplitude remains the same) is able to get longer transmission distances when the audio is processed ?  This is not a minor point because the FM commercial sucess is vinculated to the coverage area. For the first time the JAES march 2007 paper solves this aparent paradox using Mathematics.
I feel that both contributions are pertinent (complements the knolewdge about FM Broadcast) and are scientifically founded and accepted for the scientific community
Otherwise you can read my curriculum to see that at my 68 years old I do not need "promotion" like a young film star...
Oscar Bonello (oscar@alsolnet.com )  —Preceding unsigned comment added by OscarJuan (talk • contribs) 23:34, 15 March 2008 (UTC)
replies: text: By 'rigorously demonstrated', he appears to mean mathematically proven. Big deal. There has been ample empirical evidence for around 30 years, and the sudden arrival of a mathematical proof for what has been obvious, intuitive common knowledge amongst broadcast engineers for decades is neither important nor even interesting, except perhaps to other mathematicians, the paper's author and his mum. There's no consensus for these comments' inclusion and only one editor who wants them in, so I'm going to remove them. Please do not reinstate them until and unless there's a consensus here to do so. --Harumphy (talk) 16:07, 3 May 2008 (UTC)

text: side note, not related to this discussion: Galileo trial was about heliocentrism vs geocentrism, while the "flat earth" seems to be mostly a recent, modern myth. --Gabriel Bouvigne (talk) 08:11, 23 May 2008 (UTC)
thread_title:  Restore the Oscar Bonello work 

message: The article says Multiband audio processing improves the coverage area of an FM stereo station, however, this knowledge was never rigorously demonstrated prior to the work of Oscar Bonello. with a reference to a 2007 paper.    I must admit I know nothing about this subject, but it looks a bit strange that such a basic fact about such an old technology was never considered in a scientific paper before.    --The very model of a minor general (talk) 13:52, 3 May 2008 (UTC)
replies: text: By 'rigorously demonstrated', he appears to mean mathematically proven. Big deal. There has been ample empirical evidence for around 30 years, and the sudden arrival of a mathematical proof for what has been obvious, intuitive common knowledge amongst broadcast engineers for decades is neither important nor even interesting, except perhaps to other mathematicians, the paper's author and his mum. There's no consensus for these comments' inclusion and only one editor who wants them in, so I'm going to remove them. Please do not reinstate them until and unless there's a consensus here to do so. --Harumphy (talk) 16:07, 3 May 2008 (UTC)
thread_title: Fact

message: Is unfortunately for the Wikipedia future to know that:
- " I must admit I know nothing about this subject, but ... "
- " I am not a radio technical expert my any means..."
- ... and the sudden arrival of a mathematical proof for what has been obvious, intuitive common knowledge amongst broadcast engineers for decades is neither important ... "
Usually when a person recognizes itself as ignorant of some question he do not writes a single line  at any paper cyclopedia (only the best people in each field writes for the Encyclopedia Britannica by example). Usually the people that do not know about an issue the best he can do is to learn. After 30 year teaching at University I used to do the job of converting people to the full knowledge... But what can we do with you my dear friends?
Only to say:
1) About "Clearly you have a NPOVon this then?" Please read the Wiki rules. A person can write about his own work if this is published by a recognized scientific journal
2) About: "it looks a bit strange that such a basic fact about such an old technology was never considered in a scientific paper before. "  Please give me examples of previous publications. I let you know that before publication of a Paper, the most brilliant engineers of the AES Journal (New York, USA) revised all international literature in English, French, German, Italian, Spanish, Japanese and Russian. If you know a published proof previous to mine, please write it in this same page.
3) About "the sudden arrival of a mathematical proof for what has been obvious" Please note that in Science nothing is obvious. Example: It appears to be obvious during centuries that the Earth is flat, not round. Remember the Galileo trial ?  Do you know about the last Fermat theorem?  Do you know about the Tales theorem?
About specifically the FM statements. Can you explain me what is the reason that  the audio processing improves the coverage area if the power of an FM modulated signal is the same not matter the modulation percentage ?
Please explain me it !
* Robert Orban has already explained it better than I can, many times over many years. I read his papers avidly over 20 years ago when I worked as a broadcast engineer. Are you not familiar with his work? BTW, if you restore your work without consensus here first you risk being blocked for edit-warring.--Harumphy (talk) 08:20, 23 May 2008 (UTC)
replies: text: side note, not related to this discussion: Galileo trial was about heliocentrism vs geocentrism, while the "flat earth" seems to be mostly a recent, modern myth. --Gabriel Bouvigne (talk) 08:11, 23 May 2008 (UTC)
thread_title:  Prof Bonello opinion

message: In the past I just added the algebric forumala with which the Matrix DECODER acts.
I ask myself why you deleted it. It's not an industrial secret and it's even very known. Simply it was not written here in Wikipedia.
I worked in Broadcasting for a decade and I was member of S.M.P.T.E.
What I written, it' sjust the matrix Law that normally governs ( or governed in the past ) de decoding of a Stereo Signal.
What's wrong with it ? Who's the "teacher removed it" and why ?
I repeat HERE that Law:
BEFORE the multiplex era, it was transmitetd the SUM ( L+R ) and the difference ( L-R ) as written in the article.
The operation needed in order to give back L and R it was ( and it's even quite intuible, come-on! ):
* (L+R)+(L-R)=2L
* (L+R)-(L-R)=2R
Of course to obtain L and R now 
* L=0.5(2L)
* R=0.5(2R)
But it'useless.
Now, why this information was deleted ? What's wrong ?
Iw2mln (talk) 12:59, 19 August 2010 (UTC)
replies: text: I assume you mean this edit of mine: . If so, my aim was to simplify the explanation by cutting it down to its bare essentials. There's nothing 'wrong' with the matrix formulas, they just seemed, for an encyclopedic overview of the subject, an unnecessary repetition of information already given.--Harumphy (talk) 09:23, 21 August 2010 (UTC)
replies: text: yes it was exactly what you linked.I assumed that to give a clear formula, without diminishing the value of the explanation, was just better, in order to give an immediate idea. If you have a look in "Dolby" chapter, there are also forumlae. Just fro mthe latin "Formula" means: the shortest form. And I find it extremely efficient, where words are creating some confusion, sometimes, due the differences in languanges. Being Wikipedia an Enciclopedia that gives very deep details on arguments treaten, I thought it was useful to write clearly down even this formula once forever. Am I so wrong ?Iw2mln (talk) 20:17, 22 August 2010 (UTC)
replies: text:  The terms 'sum' and 'difference' are already defined in the article as meaning L+R and L-R, so I'm not sure where the confusion would arise. I agree that sometimes maths is the ideal language, but I don't think this is such a case: the concept we're describing is simple enough for prose. Clearly we have a different view and probably are not going to convince each other, so what does anyone else think?--Harumphy (talk) 22:40, 22 August 2010 (UTC)
thread_title:  Why did you delete? 

message: FM is currently a redirect to frequency modulation. That said, an non-exhaustive survey suggests that majority of incoming links are really referring to this article ((FM broadcasting) instead.
User:Georgia guy and I have been having a conversation over at Talk:FM about where the FM redirect should point.
If folks have a moment to read the conversation so far, we'd love some additional thoughts from other involved Wikipedians. Thanks in advance! —mako๛ 05:46, 27 September 2011 (UTC)
thread_title:  Target of [[FM]] Redirect 

message: It is also the name of a band.  — Preceding unsigned comment added by 173.243.32.188 (talk) 22:45, 14 May 2012 (UTC)
thread_title:  It is the name of a bar 

message: The following statement appears in Comparison of analog and digital recording:
:Analog FM broadcasts rarely have a dynamic range exceeding 50 dB, though under excellent reception conditions the basic FM transmission system can achieve just over 80dB.
I don't find any support for that in this article or any discussion of audio performance. It would be a welcome addition here. -—Kvng 16:11, 7 December 2012 (UTC)
replies: text: Sounds believable, though. About 50dB was usual for vinyl records. If you get much more, it gets lost in the background noise around the listener, especially in a car. Even if the source has more, it is likely compressed before broadcasting. Rock music starts out with low dynamic range, so maybe isn't changed. See Loudness war.  Gah4 (talk) 01:02, 6 December 2015 (UTC)
thread_title:  Audio performance 

message: Note that just adding the DSB-SC doesn't increase the modulation index. The sum is never more than the maximum of the left and right channel inputs.  It is reduced to allow for the 10% of the pilot, which does add. I suspect that the bigger problem is not enough signal to recover the pilot properly. Gah4 (talk) 00:57, 6 December 2015 (UTC)
replies: text: Continuing this, is there a reference for the 0.9 on the sum and difference signals?  That is, do stereo FM transmissions reduce their signal by 10%? In some cases, this might make them less competitive, where being louder is better.  Unlike AM, there isn't a sharp physical limit to modulation index.  The channel has 200kHz bandwidth.  I suspect that there is no 0.9, but don't have a reference. Gah4 (talk) 22:28, 11 January 2017 (UTC)
replies: text: See where it talks about 45% (for one channel alone) in this spec.  I think that's equivalent to the 0.9.  Not clear what "range is somewhat reduced" meant. Dicklyon (talk) 00:26, 12 January 2017 (UTC)
replies: text: Thanks.  Note that it does allow for up to 110% (82.5kHz) when other subcarriers are included. Also, I don't see that the 45% (or 90%) goes away for a monophonic signal. Gah4 (talk) 01:34, 12 January 2017 (UTC)
replies: text: The other appendix, on monophonic, doesn't have such a scaling.  Without needing to leave room for the subcarrier, 100% max modulation seems to be what they're saying.  Dicklyon (talk) 01:42, 12 January 2017 (UTC)
replies: text: I now added a reference to the FCC document, which more or less seems to be the same. There are complicated rules related to other (SCA) carriers, which are not easy to follow, but as with your reference, the 110% including all subcarriers seems to be there.  Gah4 (talk) 01:55, 12 January 2017 (UTC)
thread_title:  This is due to the need to lower the modulation index of the main (sum) signal to accommodate the presence of the 38 kHz DSB-SC (double side-band suppressed-carrier) subcarrier and 19 kHz pilot tone. 

message: [quote]
Quadraphonic FM[edit]
In 1969, Louis Dorren invented the Quadraplex system of single station, discrete, compatible four-channel FM broadcasting. There are two additional subcarriers in the Quadraplex system, supplementing the single one used in standard stereo FM. 
[\unquote]
It never ceases to amaze me:
THAT QUADROPHONIC system, is actually "flawed" - and is also incorrectly named as a quadrophonic system
Oh yes.. it "does" utilise a type of four channel matrix.
BUT one totally different to the one discovered to "naturally exist" in ANY standard 2ch FM or any other type of stereo recording/broadcast.
SINCE 1965.
As well as for many years prior to that date.
In 1965.
A natural quadrophonic system was discovered to actually exist - IN NATURAL "stereo" AUDIO.
1/ L ch;
2/ R ch;
3/ SUMMATION of L+R = CENTRE FRONT MONO = standard FM MONO as well as previously used AM MONO:
4/ The "differential" which naturally "exists" between the difference of the R/L channels, which inversely super imposed on each other, to "self cancel" the summated EQUAL signals / sounds and to amplify the difference.
ie:
The fourth channel is DIRECTLY OPPOSITE the centre front, and is thus the TRUE centre rear.
THAT was always possible, right from the outset of the first usage of two channel stereo in 1934.
It just took on a whole different meaning - when utilised differently.. in 1965.
When it formed the basis - of discovering 25 channel surround sound.
A system utilised since 1965 COMMERCIALLY.
An all ANALOGUE "multiple channel surround sound system
Playable DIRECT off the back of any "normal" 2ch grounded earth return speaker system amplifier's outputs of a L+R and the speaker return cable being the E (earthed "chassis/ground-return") 3 wire "wiring" method.
Any two channel stereo amplifier system, which is able to utilise a 3wire feeder to feed two high potential L+R signals, whilst both channels utilise the SAME common-grounded-earth-return "wire", to return back to the amplifiers chassis/speaker -ve terminals, whereby the metallic chassis of a vehicle, or a common grounded wire in a building, IS and thus enables - the two speaker circuit's to return, back to the amplifier's speaker output 0v (-ve) terminals, is in fact  a multiple channel amplifier USED as just a standard 2ch speaker output device.
Since the inception of stereo (2ch) outputs in 1934 FRONT / LEFT / RIGHT / REAR (natural quadrophonic has been totally possible).
To state that someone "discovered" quadrophonic in 1969, AND that it was thus the quadrophonic of FM transmissions..? Was not strictly true.
Oh sure, someone found an alternative four channel FR / RR/ FL /RL "system" - but that type of sytem utilises a different decoding method to that NATURALLY FOUND, within any true 2ch stereo signal.
The true quadrophonic FRONT/LEFT/RIGHT/BACK system is a natural effect of summation and differential.
As fully explained by some OTHER audio expert earlier here in "talk"
Re:
https://en.wikipedia.org/wiki/Talk:FM_broadcasting#Why_did_you_delete.3F
As a NATURAL "FRONT/BACK/LEFT/RIGHT" "true quadrophonic" has and always will "exist" in any medium, or recorded sound format, or FM Radio stereo broadcast signal.
(irrespective as to the modern (digital thinkers) definitions of: FR/RR + FL/RL is somehow NOW having to be the NEW normal "normal quadrophonic".
No - that is just a variant. It isn't the natural method of obtaining true quadrophonic, that has existed since 1934, when stereo was first discovered to be usable.
And- the summation/ differential (natural) quadrophonic method, of obtaining FOUR different discrete autonomous channels, is:
Easily obtained anywhere, from ANY format (or recorded medium/playback method ever devised) of a "playable" 2ch stereo AUDIO SOUND.
Sorry.
But that "fact" is in existence now, and has been utilised commercially, since 1965.
Provable beyond any shadow of doubt, by a 1968 hand built electric filament "globe" LIGHTING display panel - which, when ELECTRICALLY connected via three single wires ONLY (or as two ch stereo, using two speaker "twin twist" supply cables with their earth returns electrically BONDED together):
"That system will "automatically" provide up to, and including, NINE "full frequency" (discrete & semi independent / autonomous) channels, of quadrophonic audio.
Direct off the 2ch speaker output terminals of a standard 2ch OUTPUT DEVICE, such as an amplifier:
To thus play any 2ch stereo medium, in NINE channel "analogue" surround sound (naturally) via any source.
Such as shown AND heard, in this irrefutable video (playing on Facebook) which utilises the correct audio track, which thus produces the "electrical currents" for driving these ten filament globes - to partial or full ELECTRICAL brightness, (as that circuit is wired to the MES Bakelite bases, which hold the ten small lights).
re:
https://www.facebook.com/keith.clare1/videos/112660602154778/
(visually showing HOW this electrical current is originally intended to power speaker voice-coils, when normally sent OUT into the stereo system's "own" two speaker voice coil circuits.)
Thus having digital audio experts whom disagree (here - who don't know how to HEAR = with their eyes), is tantamount to:
Just stating that "it isn't possible", to get ANY multiple ANALOGUE audio stereophonic channels, effective, from audio supplied via L/R stereo systems (or amplifiers)?
Which is also akin, to one putting (audio) blinkers on your ears, AND on your thinking:
By "stating" the NATURAL (analogue) audio "sound" is impossible (similar to still calling the world NOT ROUND - BUT FLAT).
?
Unfortunately for the "Nay-Sayers":
Since 1999 there has even been a NZ Company - selling and installing just such a system.
(being the one "discovered in 1965", that does exist AND OPERATE, as a fully functional commercially viable "analogue" multiple channel surround sound system).
There is NOW way too much verifiable proof, to "include it all here"
So - if you want it, then go get it yourself:
Put this keyword into any halfway decent internet "browser"  and discover for yourself.:
@QUIXNZ
And that a NZ Company has been since 1999, manufacturing a commercial method/ product - providing analogue surround sound, the 1965 way.
The same New Zealand Company (which uses that system), whose NZ owner "discovered/invented" - a NATURAL quadrophonic system, suitable for the masses. 
(ie: "The masses" = the general public ... world wide)
A system so easy as to be UNABLE to be found, by so-called audio experts who went "digital" (after a certain Ray D, found that he could suppress high end audio "noise" by inserting something he called noise reduction technology, "basically a capacitor", into tape players/ recorders, to avoid the user hearing high frequency TAPE HISS).
Digital audio can also be FURTHER analogue decoded, into multiple channel surround sound, in higher channel numbers than the digital medium provides.
By the exact same system:
Found / discovered/ invented - in 1965, being a full (4) FOUR YEARS "quadraphonicly speaking", before this article's so called QUADROPHONIC invention date of 1969.
This "section" should NOT be titled as:
QUADROPHONIC
But as:
QUADRAPLEX
As:
The Inventor: Louis Dorren, in 1969, did in fact NOT invent a QUADRAPHONIC SYSTEM - but a "Quadraplex" system. (two entirely different operating principals)
THERE IS A HUGE DIFFERENCE BETWEEN THOSE TWO WORDS.. and (thus) their actual technical meanings COMPLETELY differ as well, too.
115.188.58.240 (talk) 23:20, 9 August 2016 (UTC)
thread_title:  Re: Quadraphonic FM[edit] 

message: The article indicates the the stereo subcarrier is sine(4*pi*pilot).  The quadraphonic section indicates that the  (left-right) part is on a cosine subcarrier.  This is the part that will be decoded by stereo receivers, so should be sine.  Is there a reference for the details of the quadraphonic signal?  Maybe the patent number? Gah4 (talk) 07:26, 19 October 2016 (UTC)
thread_title:  Quadraphonic phase 

message: It's shown in this picture https://upload.wikimedia.org/wikipedia/commons/thumb/c/cd/RDS_vs_DirectBand_FM-spectrum2.svg/600px-RDS_vs_DirectBand_FM-spectrum2.svg.png but I can't find any information about the service it provides. Is it audio? Is it data? Of the extra services provided in the FM band, only RBDS and DirectBand have any explanation on Wikipedia. In fact, not only can I find no info on Wikipedia about Audos, I can't find any information about it anywhere else on the internet at all. And I just looked it up in Google. If somebody here knows what it is, please post the info. Thanks in advance. Benhut1 (talk) 11:27, 19 February 2017 (UTC)
replies: text: 67kHz used to be SCA, I don't know about DirectBand, and also never heard of Audos.  Is it a company? Gah4 (talk) 23:26, 19 February 2017 (UTC)
replies: text:  has a similar graph, copied from Wikipedia, saying audio in that spot. Gah4 (talk) 23:35, 19 February 2017 (UTC)
thread_title:  What's the Audos Subcarrier? 

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thread_title:  External links modified 

message: I removed a  note because I think it isn't needed, but because I can't figure out what it applies to.  The nearest statement is obvious enough (from inverse square law), but earlier statements in the paragraph might need one.  Gah4 (talk) 23:57, 22 November 2017 (UTC)
thread_title:  {{citation needed|date=June 2016}} 

message: Anyone know the frequency tolerance for FM carriers?  At one point the article says exact multiples of 100kHz, but there is a tolerance on them. As well as I remember, 1kHz, but that might be TV or something else. Gah4 (talk) 20:01, 20 August 2019 (UTC)
replies: text: OK, I found it.  (It isn't always easy to find things in fcc.gov.)  It seems to be 2kHz for over 10 watts, and 3kHz for 10 watts or less. I don't know about other countries. Gah4 (talk) 20:12, 20 August 2019 (UTC)
replies: text: +/-2kHz in general.  That is the spec here in the UK and I am pretty sure it is in the ETSI specs somewhere. There is separate spec for frequency drift over time which is 200-300Hz depending on what standard you look at.Davidbstanley (talk) 21:19, 21 August 2019 (UTC)

text: The 'worldwide view' is that tolerances for all radio services are listed in Appendix 2 to the ITU Radio Regulations. For FM broadcast transmitters it's 2kHz if the power is greater than 50W. If it's 50W or less, it's relaxed to 3kHz. National regulations may be tighter. Harumphy (talk) 20:09, 24 August 2019 (UTC)
replies: text: The reason for the question was the work "exact" in multiples of 100kHz. Maybe I can just remove exact. Gah4 (talk) 15:23, 26 August 2019 (UTC)
replies: text: Make sure not to confuse the spacing which is an exact multiple of 100kHz or 200kHz with the tolerance which I think most would understand to be the accuracy of the average (or un-modulated) carrier frequency.  The spacing is a specification, so it can be given as an exact figure, just like the licensed frequency.  The actual frequency of a real transmitter will have an error or tolerance, which should typically be within 2kHz of the licensed frequency. Having said all that, the edit you made in the article is perfectly reasonable! Davidbstanley (talk) 21:06, 26 August 2019 (UTC)
replies: text: Yes, I could have said assigned frequency or licensed frequency instead.  That seemed to be the complicated way to get the idea across.  It gets interesting with digital tuners, which will only tune to the appropriate values (within tolerance).  Take one to another country, and you are stuck!  Thanks.  Gah4 (talk) 22:30, 26 August 2019 (UTC)
replies: text: There is a real issue with exporting radios between different markets.  It is not mentioned in the article and probably should be.  It is a particular issue with vehicles exported from the US.  I know of stations in a some countries that have changed frequencies to odd multiples of 100kHz because of this. Davidbstanley (talk) 06:55, 27 August 2019 (UTC)
thread_title:  tolerance 

message: The article says: a 75 µs audio pre-emphasis, a technical innovation that became part of the original FM Stereo Multiplex Standard.  Was preemphasis really not added until the stereo subcarrier was added?  That would make the signal not compatible with existing mono receivers, which I don't think they would have done. Gah4 (talk) 07:14, 21 December 2019 (UTC)
replies: text: I had also wondered about that, but I do not know the answer.  Some old documentation is needed.  The old fashioned tone control used on many radios would have sufficiently dealt with the boost in high frequencies though.Davidbstanley (talk) 08:19, 21 December 2019 (UTC)
replies: text: this one seems to indicate that the 75us preemphasis existed previously, though maybe not enough to be a WP:RS. Gah4 (talk) 10:10, 1 January 2020 (UTC)

text: It's not worded very well. Pre-emphasis has always been used with mono FM in the 87.5-108 MHz band. Stereo came later and needed to use it too, if only to maintain compatibility with mono receivers. Harumphy (talk) 14:05, 2 January 2020 (UTC)
replies: text: Though it is fair to assume pre-emphasis has always been used, there really needs to be some document that says that.  The engineering handbook does sort of say that.  Another way forward would be to get some receiver circuit diagrams that pre-date stereo and look for the de-emphasis components. Davidbstanley (talk) 20:19, 2 January 2020 (UTC)
replies: text: Here's a BBC research paper that shows that 75us in the US and 50us in the UK had been adopted by January 1946: https://www.bbc.co.uk/rd/publications/rdreport_1946_04 Harumphy (talk) 11:48, 3 January 2020 (UTC)
replies: text: Excellent.  To me that paper is all that is needed to improve the pre-emphasis section of the main article and to use as a reference.  If no one else beats me to it, I will have a go when I get a chance. Davidbstanley (talk) 17:24, 3 January 2020 (UTC)
replies: text: I thought about doing it last night, be then kept on reading the paper.  Other than a bad typewriter that makes e look like o, it is pretty interesting to see what they thought and knew back then.  It would be nice to have an FCC reference way back then, also, but I don't know where to find those. Gah4 (talk) 18:33, 3 January 2020 (UTC)
replies: text: I have made some edits and also have added a sentence which cites the BBC paper.  It is a fascinating read considering its age and just how much they knew, understood and got right. Davidbstanley (talk) 21:51, 3 January 2020 (UTC)

text: this one is the schematic for a mono tuner. Note that in the later mono, early stereo days, it was usual to supply a "MPX output" which is before the de-emphasis.  (Which I just remembered, seeing it on that one.) This allows for an external stereo decoder.  The filter after the MPX output looks like 68us, but there might be other capacitance around that the designers include. In any case, the reason for MPX output was to bypass the de-emphasis, which means it was there to bypass. Gah4 (talk) 20:39, 2 January 2020 (UTC)
replies: text: Discussion about field strength from 1946 had me wondering about more recent measurements on field strength.  I then found this one which describes more modern field strength measurements. This might also be a good reference for the article. Gah4 (talk) 02:26, 4 January 2020 (UTC)
thread_title:  preemphasis 

message: A discussion is taking place to address the redirect :Noise reduction in radio broadcasting. The discussion will occur at Wikipedia:Redirects for discussion/Log/2020 August 20#Noise reduction in radio broadcasting until a consensus is reached, and readers of this page are welcome to contribute to the discussion.  Steel1943 (talk) 06:54, 20 August 2020 (UTC)
thread_title:  "Noise reduction in radio broadcasting" listed at [[Wikipedia:Redirects for discussion|Redirects for discussion]] 

message: The image claims to show DirectBand subcarriers.  However, I believe that it is in fact showing the HD Radio carriers.  As such it either needs changing or deleting from this article.  It makes the same claim and error in the DirectBand article. Davidbstanley (talk) 21:04, 13 March 2023 (UTC)
thread_title:  FM station subcarriers on SDRpp spectrogram