Zweikanalton
 | This articleneeds additional citations forverification.(September 2014) |
Zweikanalton( "two-channel sound" ) orA2 Stereo,[1]is an analogtelevisionsound transmission system used inGermany,Austria,Australia,Switzerland,Netherlandsand some other countries that use or usedCCIR systems.South Koreautilized a modified version of Zweikanalton for theNTSCanalog television standard. It relies on two separateFMcarriers.
This offers a relatively high separation between the channels (compared to asubcarrier-basedmultiplexingsystem) and can thus be used forbilingualbroadcasts as well asstereo.Unlike the competing NICAM standard, Zweikanalton is ananalogsystem.
How it works[edit]
A2nd FM sound carriercontaining the right channel for stereo is transmitted at a frequency 242 kHz higher than the existingmonoFM sound carrier, and channel mixing is used in the receiver to derive the left channel.
The second sound carrier also contains a 54.6875 kHz pilot tone to indicate whether the transmission is stereo or bilingual.
The pilot tone is 50% amplitude-modulated with 117.5 Hz for stereo or 274.1 Hz for bilingual.
| mode | existing BG 5.5 MHz or DK 6.5 MHz sound carrier contains: | 2nd BG 5.742 MHz or DKa6.258 MHz/6.742 MHz/5.742bMHz 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 kHz 50% AM with 117.5 Hz |
| bilingual | 1st language | 2nd language | 54.6875 kHz 50% AM with 274.1 Hz |
- a.^The second sound carrier frequency of DK systems varies from country, and sometimes manufacturers divide them into DK1/DK2/DK3 systems.[2][3]
- 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 thesignal-to-noise ratioby 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 Hz = 242187.5 Hz) which, being an odd multiple of half line frequency, reduces the visibility ofintermodulationproducts between the two carriers. The pilot tone frequency is 3.5 times line frequency (54687.5 Hz). The modulated tone frequency is 117.50 Hz for stereo transmission and 274.1 Hz for bilingual transmission. Absence of this tone is interpreted as a monaural transmission.
System M variant[edit]
There is a modified version of Zweikanalton used inSouth Korea,compatible with the NTSCSystem Mstandard of TV transmission. In this case the second FM carrier is 14.25 times the line frequency, or about 224 kHz, above the first carrier; pre-emphasis is 75 microseconds; the stereo pilot tone frequency is 149.9 Hz; the bilingual pilot tone frequency is 276 Hz; and the second channel carries L-R (not R).
History[edit]
Zweikanalton was developed by theInstitut für Rundfunktechnik(IRT) in Munich during the 1970s, and was first introduced on the German national television channelZDFon 13 September 1981. The German public broadcasterARDsubsequently introduced Zweikanalton on itsDas Erstechannel on 29 August 1985 in honour of the 1985 edition of theInternationale Funkausstellung Berlin(IFA). West Germany thus became the first country in Europe to usemultiplexed soundon its television channels.
TV3 Malaysiaused Zweikanalton on its UHF analogue transmission frequency (Channel 29), whileNICAMwas instead used on its VHF analogue transmission frequency (Channel 12).
As a result of the analogue television switch-off in most countries which used Zweikanalton, Zweikanalton is now considered obsolete and has been replaced withMPEG-2and/orMPEG-4for countries that have converted toDVB-T/DVB-T2(Europe and Asia-Pacific), andDolby DigitalAC-3 onATSCin South Korea.
Other names[edit]
Zweikanalton is known by a variety of names worldwide. Most commonly used names areZweiton,German Stereo,A2 Stereo,West German StereoandIGR Stereo.
See also[edit]
- Multichannel Television Sound(3 additional audio channels on 4.5 MHz audio carriers)
- NICAM
- EIAJ MTS
Notes and references[edit]
- ^Stereo sound systems - QSL.netArchived2010-12-03 at theWayback Machine
- ^US 7751571B2,Hyun Ho Jeong, "Sound signal processor and method for processing sound signal using the same", published 2006-03-07, issued 2010-07-06, assigned to LG ELECTRONICS INC
- ^US 8090110B2,Tien-Ju Tsai; Shih-Chuan Lu & Shu-Ming Liu, "Method and apparatus for determining sound standard for input sound signal", published 2009-10-22, issued 2012-01-03, assigned to Himax Technologies Ltd