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((Refimprove|date=September 2014))
[[File:DOG Zweikanalton ORF eins.svg|thumb|[[Digital on-screen graphic]] displayed at the beginning of Zweikanalton programmes on [[ORF 1]]]]

'''Zweikanalton''' ("two-channel sound") or '''A2 Stereo''',<ref>[http://www.qsl.net/zl1wtt/stereo.htm Stereo sound systems - QSL.net] ((webarchive |url=https://web.archive.org/web/20101203204850/http://www.qsl.net/zl1wtt/stereo.htm |date=2010-12-03 ))</ref> is an analog [[television]] sound transmission system used in [[Germany]], [[Austria]], [[Australia]], [[Switzerland]], [[Netherlands]] and some other countries that use or used [[PAL#PAL broadcast systems|PAL]]-B or PAL-G. [[TV3 (Malaysia)|TV3 Malaysia]] formerly used Zweikanalton on its UHF analogue transmission frequency (Channel 29), while [[NICAM]] was instead used on its VHF analogue transmission frequency (Channel 12). [[South Korea]] also formerly utilised a modified version of Zweikanalton for its [[NTSC]] analogue television system until 31 December 2012. It relies on two separate [[Frequency modulation|FM]] [[carrier wave|carriers]].

This offers a relatively high separation between the channels (compared to a [[subcarrier]]-based [[multiplexing]] system) and can thus be used for [[bilingual]] broadcasts as well as [[stereophonic sound|stereo]]. Unlike the competing NICAM standard, Zweikanalton is an [[Analog television|analog]] system.

== How it works ==
A '''2nd FM sound carrier''' containing the right channel for stereo is transmitted at a frequency 242&nbsp;kHz higher than the existing [[monoaural|mono]] FM sound carrier, and channel mixing is used in the receiver to derive the left channel.

The second sound carrier also contains a 54.6875&nbsp;kHz pilot tone to indicate whether the transmission is stereo or bilingual.

The pilot tone is 50% amplitude-modulated with 117.5&nbsp;Hz for stereo or 274.1&nbsp;Hz for bilingual.

{| class="wikitable"
|-
! mode !! existing BG 5.5&nbsp;MHz or DK 6.5&nbsp;MHz sound carrier contains:   !!  2nd BG 5.742&nbsp;MHz or DK((ref|a|a)) 6.258&nbsp;MHz/6.742&nbsp;MHz/5.742((ref|b|b))&nbsp;MHz carrier contains: !!  pilot tone in 2nd carrier:
|-
| mono || mono || carrier is absent || none
|-
| stereo || mix of left & right (L+R) || right audio channel (R) || 54.6875&nbsp;kHz 50% AM with 117.5&nbsp;Hz
|-
| bilingual || 1st language || 2nd language || 54.6875&nbsp;kHz 50% AM with 274.1&nbsp;Hz
|}
:a.((note|a))The second sound carrier frequency of DK systems varies from country, and sometimes manufacturers divide them into DK1/DK2/DK3 systems.<ref>((cite patent |country=US |number=7751571B2 |title=Sound signal processor and method for processing sound signal using the same |pubdate=2006-03-07 |gdate=2010-07-06 |fdate=2006-03-07 |pridate=2005-12-01 |inventor=Hyun Ho Jeong |assign1=LG ELECTRONICS INC))</ref><ref>((cite patent |country=US |number=8090110B2 |title=Method and apparatus for determining sound standard for input sound signal |pubdate=2009-10-22 |gdate=2012-01-03 |fdate=2008-04-21 |pridate=2008-04-21 |invent1=Tien-Ju Tsai |invent2=Shih-Chuan Lu |invent3=Shu-Ming Liu |assign1=Himax Technologies Ltd))</ref>
:b.((note|b))The video bandwidth is reduced.

Zweikanalton can be adapted to any existing analogue television system, and modern PAL or SECAM television receivers generally include a sound detector IC that can decode both Zweikanalton and NICAM.

Zweikanalton can carry either a completely separate audio program, or can be used for stereo sound transmission. In the latter case, the first FM carrier carries (L+R) for compatibility, while the second carrier carries R (not L-R.) After combining the two channels, this method improves the [[signal-to-noise ratio]] by reducing the correlated noise between the channels.

The frequencies are chosen such that they cause minimal interference to the picture. The difference between the two sound carriers is 15.5 times the line frequency (15.5 x 15625&nbsp;Hz = 242187.5&nbsp;Hz) which, being an odd multiple of half line frequency, reduces the visibility of [[intermodulation]] products between the two carriers. The pilot tone frequency is 3.5 times line frequency (54687.5&nbsp;Hz). The modulated tone frequency is 117.50&nbsp;Hz for stereo transmission and 274.1&nbsp;Hz for bilingual transmission. Absence of this tone is interpreted as a monaural transmission.

== System M variant ==
There is a modified version of Zweikanalton used in [[South Korea]], compatible with the NTSC [[CCIR System M|System M]] standard of TV transmission. In this case the second FM carrier is 14.25 times the line frequency, or about 224&nbsp;kHz, above the first carrier; pre-emphasis is 75 microseconds; the stereo pilot tone frequency is 149.9&nbsp;Hz; the bilingual pilot tone frequency is 276&nbsp;Hz; and the second channel carries L-R (not R).

== History ==
Zweikanalton was developed by the ((Lang|de|[[Institut für Rundfunktechnik]]|italic=no)) (IRT) in Munich during the 1970s, and was first introduced on the German national television channel [[ZDF]] on 13 September 1981. The German public broadcaster [[ARD (broadcaster)|ARD]] subsequently introduced Zweikanalton on its [[Das Erste]] channel on 29 August 1985 in honour of the 1985 edition of the [[IFA Berlin|Internationale Funkausstellung Berlin]] (IFA). West Germany thus became the first country in Europe to use [[Sound multiplex in broadcasting|multiplexed sound]] on its television channels. 

As a result of the analogue television switch-off in most countries which used Zweikanalton during 2006–2019, Zweikanalton is now considered obsolete and has been replaced with [[MPEG-2]] and/or [[MPEG-4]] for countries that have converted to DVB-T/DVB-T2 (Germany, Austria, Australia, Switzerland, Netherlands, Malaysia), and [[Dolby Digital]] AC-3 for countries that have converted to ATSC (South Korea).

== Other names ==
Zweikanalton is known by a variety of names worldwide. Most commonly used names are ''Zweiton'', ''German Stereo'', ''A2 Stereo'', ''West German Stereo'' and ''IGR Stereo''.

== See also ==
*[[Multichannel Television Sound]] (3 additional audio channels on 4.5 Mhz audio carriers)
*[[NICAM]]
*[[EIAJ MTS]]

==Notes and references==
((reflist))

((Video formats))
((Analogue TV transmitter topics))

[[Category:Broadcast engineering]]
[[Category:Television technology]]

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