Editing Stereophonic sound (section)

===Radio===

====Early experimentation====
The earliest approach to stereo (then commonly called ''binaural'') radio used two separate transmissions to individually send the left and right audio channels, which required listeners to operate two receivers in order to hear the stereo effect. In 1924 [[Franklin M. Doolittle]] was issued U.S. patent 1,513,973<ref>{{patent|US|1513973}} "Radiotelephony". Patent issued November 4, 1924, to Franklin M. Doolittle for application filed February 21, 1924.</ref> for the use of dual radio transmissions to create stereo reception. That same year Doolittle began a year-long series of test transmissions, using his [[medium wave]] broadcasting station, [[WPAJ]] in New Haven, Connecticut, which was temporarily authorized to concurrently operate a second transmitter. Left and right audio was distributed to the two transmitters by dual microphones, placed about {{convert|7|inches|cm}} apart in order to mimic the distance between a person's ears.<ref>[https://books.google.com/books?id=onFEAQAAIAAJ&pg=PA867 "Binaural Broadcasting"] {{Webarchive|url=https://web.archive.org/web/20240806001647/https://books.google.com/books?id=onFEAQAAIAAJ&pg=PA867#v=onepage&q&f=false |date=August 6, 2024 }} by F. M. Doolittle, ''Electrical World'', April 25, 1925, pages 867–870. The transmitting wavelengths of 268 and 227 meters correspond to frequencies of 1120 (WPAJ's normal frequency) and 1320 kHz respectively.</ref><ref>[https://commons.wikimedia.org/wiki/File:Stereoscopic_or_Binaural_Broadcasting_in_Experimental_Use_at_New_Haven,_Cincinnati_Enquirer,_March_22,_1925.pdf "Stereoscopic or Binaural Broadcasting in Experimental Use at New Haven"] {{Webarchive|url=https://web.archive.org/web/20220107185042/https://commons.wikimedia.org/wiki/File:Stereoscopic_or_Binaural_Broadcasting_in_Experimental_Use_at_New_Haven,_Cincinnati_Enquirer,_March_22,_1925.pdf |date=January 7, 2022 }} (correspondence from Franklin M. Doolittle), ''Cincinnati (Ohio) Enquirer'', March 22, 1925, Section 6, page 6.</ref> Doolittle ended the experiments primarily because a lack of available frequencies on the congested AM broadcast band which meant that it was not practical for stations to occupy two frequencies,<ref name="binaural"/> plus it was cumbersome and expensive for listeners to operate two radio receivers.<ref name="binaural">[https://archive.org/stream/broadcastingtele43unse_0#page/n518/mode/1up/ "Binaural Broadcasting"] by Franklin M. Doolittle, ''Broadcasting'', November 3, 1952, page 97.</ref>

In 1925 it was reported that additional experimental stereo transmissions had been conducted in Berlin, again with two mediumwave transmissions.<ref>[https://books.google.com/books?id=yHg1AQAAIAAJ&pg=PA416 "Radio Stereophony"] {{Webarchive|url=https://web.archive.org/web/20240625173733/https://books.google.com/books?id=yHg1AQAAIAAJ&pg=PA416 |date=June 25, 2024 }} by Ludwig Kapeller, ''Radio News'', October 1925, pages 416, 544–546. The transmitting wavelengths of 430 and 505 meters correspond to approximately 698 and 594 kHz respectively.</ref> In December of that year the [[BBC]]'s [[long wave]] station, 5XX in [[Daventry, Northamptonshire]], participated in the first British stereo broadcast{{snd}} a concert from [[Manchester]], conducted by [[Hamilton Harty|Sir Hamilton Harty]]{{snd}} with 5XX transmitting nationally the right channel, and local BBC stations broadcasting the left channel on mediumwave.<ref>[https://worldradiohistory.com/UK/Wireless-and-Wireless-Weekly/Wireless-1925-09-26-S-OCR.pdf#page=3 "Stereoscopic Broadcasting"] {{Webarchive|url=https://web.archive.org/web/20210310042905/https://worldradiohistory.com/UK/Wireless-and-Wireless-Weekly/Wireless-1925-09-26-S-OCR.pdf#page=3 |date=March 10, 2021 }} by Captain H. J. Round, ''Wireless'', September 26, 1925, pages 55–56.</ref> The BBC repeated the experiment in 1926, using 2LO in London and 5XX at Daventry. On June 12, 1946, a similar experimental broadcast using two stations was conducted in Holland, which was mistakenly thought to be the first in Europe and possibly the world.<ref>[https://babel.hathitrust.org/cgi/pt?id=mdp.39015016421656&view=1up&seq=382 "Dutch Regard 'Stereophonic Broadcasting' Experiment as Significant for Future"], {{Webarchive|url=https://web.archive.org/web/20210311033206/https://babel.hathitrust.org/cgi/pt?id=mdp.39015016421656&view=1up&seq=382 |date=March 11, 2021 }}, ''Foreign Commerce Weekly'', August 24, 1946, page 16.</ref>

1952 saw a renewed interest in the United States in stereo broadcasting, still using two stations for the two channels, in part in reaction to the development of two-channel tape recordings. The [[Federal Communications Commission]]'s (FCC) ''duopoly'' rule limited station owners to one AM station per market. But many station owners now had access to a co-owned FM station, and most of these tests paired AM and FM stations. On May 18 [[KNWN (AM)|KOMO]] and KOMO-FM in Seattle, Washington conducted an experimental broadcast,<ref>[https://archive.org/stream/broadcastingtele42unse_0#page/n1081/mode/1up "KOMO Binaural"] ''Broadcasting'', June 2, 1952, page 46.</ref> and four days later Chicago AM radio station [[WGN (AM)|WGN]] and its sister FM station, WGNB, collaborated on an hourlong stereophonic demonstration.<ref>[https://archive.org/stream/broadcastingtele42unse_0#page/n992/mode/1up "Binaural Feature at Parts Show"], ''Broadcasting'', May 26, 1952, page 73.</ref> On October 23, 1952, two Washington, D.C. FM stations, [[WTOP-FM|WGMS-FM]] and [[WASH (FM)|WASH]], conducted their own demonstration.<ref>[https://chroniclingamerica.loc.gov/lccn/sn83045462/1952-10-24/ed-1/seq-24/ "2 Stations, 2 Mikes, 2 Radios Give Broadcast Realistic Sound"] {{Webarchive|url=https://web.archive.org/web/20210316215111/https://chroniclingamerica.loc.gov/lccn/sn83045462/1952-10-24/ed-1/seq-24/ |date=March 16, 2021 }}, ''Washington (D.C.) Evening Star'', October 24, 1952, page A-24.</ref> Later that month New York City's [[WFME (AM)|WQXR]], paired with [[WQXR-FM]], initiated its first stereophonic broadcast, which was relayed to [[WDRC (AM)|WDRC]]{{refn|group=note|Franklin Doolittle's former WPAJ, now located in Hartford, Connecticut}} and [[WHCN|WDRC-FM]].<ref>"Two WDRC Stations Will Present 'Binaural' System Demonstrations", ''Hartford Courant'', October 29, 1952, page 26.</ref><ref>[https://archive.org/stream/broadcastingtele43unse_0#page/n974/mode/1up "WDRC"] (advertisement), ''Broadcasting'', December 8, 1952, page 9.</ref> By 1954, WQXR was broadcasting all of its live musical programs in stereophonic sound, using its AM and FM stations for the two audio channels.<ref>Multiple sources:
*"News of TV and Radio", ''The New York Times'', October 26, 1952, p. X-11.
* "Binaural Devices", ''The New York Times'', March 21, 1954, p. XX-9.</ref> [[Rensselaer Polytechnic Institute]] began a weekly series of live stereophonic broadcasts in November 1952 using two AM stations, [[WHAZ (AM)|WHAZ]] in conjunction with a very low-powered local [[carrier current]] station, which meant the stereo listening area did not extend beyond the college campus.<ref>[https://books.google.com/books?id=3y0DAAAAMBAJ&pg=PA20 "Binaural Music on the Campus"], {{Webarchive|url=https://web.archive.org/web/20240806001623/https://books.google.com/books?id=3y0DAAAAMBAJ&pg=PA20#v=onepage&q&f=false |date=August 6, 2024 }}, ''Popular Science'', April 1953, p. 20.</ref>

The revived dual transmitter tests were of limited success, because they still required two receivers, and with AM-FM pairings the sound quality of the AM transmissions was generally significantly inferior to the FM signals.

====FM standards====
[[File:Scott350.jpg|thumb|[[HH Scott]] Model 350, c. 1961: the first FM stereo tuner sold in the U.S.]]

The Zenith-GE [[Pilot signal|pilot-tone]] stereo system is used throughout the world by [[FM broadcasting]] stations.

It was eventually determined that the bandwidth assigned to individual FM stations was sufficient to support stereo transmissions from a single transmitter. In the United States, the FCC oversaw comparison tests, conducted by the National Stereophonic Radio Committee, of six proposed FM standards. These tests were conducted by [[WLTJ|KDKA-FM]] in Pittsburgh, Pennsylvania during July and August 1960.<ref>{{cite web |title= Commentary: Dick Burden on FM Stereo Revisited |url= http://www.rwonline.com/article/812 |archive-url= https://archive.today/20120910150332/http://www.rwonline.com/article/812 |url-status= usurped |archive-date= 2012-09-10 |date= February 1, 2007 |publisher= Radio World |access-date= February 10, 2021 }}</ref> In April 1961 the FCC adopted stereophonic FM technical standards, largely based on a Zenith-General Electric proposal, with licensed regular stereophonic FM radio broadcasting set to begin in the United States on June 1, 1961.<ref>[https://archive.org/stream/broadcastingtele60unse_0#page/n442/mode/1up/ "Finally, FCC Okays Stereo"], ''Broadcasting'', April 24, 1961, pages 65–66.</ref> At midnight in their respective time zones on June 1, General Electric's [[WRVE|WGFM]] in Schenectady, New York, Zenith's [[WUSN|WEFM]] in Chicago, and [[KKLQ (FM)|KMLA]] in Los Angeles became the first three stations to begin broadcasting using the new stereo standards.<ref>[https://archive.org/stream/broadcastingtele60unse_0#page/n1189/mode/1up "Three fms meet date for multiplex stereo"], ''Broadcasting'', June 5, 1961, page 58.</ref>

Following experimental FM stereo transmissions in the London area in 1958 and regular Saturday morning demonstration transmissions using TV sound and medium wave (AM) radio to provide the two channels, the first regular BBC transmissions using an FM stereo signal began on the [[BBC Third Programme]] network on August 28, 1962.<ref>[https://www.bbc.co.uk/historyofthebbc/anniversaries/august#heading-start-of-experimental-stereo-broadcasting-28-august-1962 Start of experimental stereo broadcasting 28 August 1962] {{Webarchive|url=https://web.archive.org/web/20181119060935/https://www.bbc.co.uk/historyofthebbc/anniversaries/august#heading-start-of-experimental-stereo-broadcasting-28-august-1962 |date=November 19, 2018 }}, BBC</ref>

In Sweden, [[Televerket (Sweden)|Televerket]] invented a different stereo broadcasting system called the ''Compander System''. It had a high level of channel separation and could even be used to broadcast two separate mono signals{{snd}} for example for language studies (with two languages at the same time). But tuners and receivers with the pilot-tone system were sold so people in southern Sweden could listen to, for example, Danish radio. At last Sweden (the Televerket) decided to start broadcasting in stereo according to the pilot-tone system in 1977.

====AM standards====
Very few stations transmit in [[AM stereo]]. This is in part due to the limited audio quality afforded by the format, and the scarcity of AM stereo receivers. Various modulation schemes are used for AM stereo, of which the best-known is [[Motorola]]'s [[C-QUAM]], the official method for most countries in the world where AM stereo transmission is available. There has been experimental AM adoption of digital [[HD Radio]], which also allows the transmission of stereo sound on AM stations;<ref>{{cite news |title=WWFD 820&nbsp;AM becomes first all-digital AM station |date=16 July 2018 |website=Radio-Online |url=https://news.radio-online.com/cgi-bin/rol.exe/headline_id=n35675}}</ref><ref>{{cite press release |title=FCC authorizes all-digital AM radio |date=27 October 2020 |publisher=[[Federal Communications Commission]] |url=https://docs.fcc.gov/public/attachments/DOC-367780A1.pdf |access-date=2020-10-27}}</ref> HD Radio's lack of compatibility with C-QUAM along with other interference issues has hindered HD Radio's use on the AM dial.