Zweikanalton
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Zweikanalton( "two channel sound" ) orA2 Stereo,[1]is atelevisionsound transmission system used inGermany,Austria,Switzerland,Netherlandsand other countries that use or usedPAL-B or PAL-G.South Koreaformerly utilised its variant of this format in analogue television system until 31 December 2012. 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 competingNICAMstandard, Zweikanalton is ananalogsystem.
How It Works
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% AM modulated with 117.5 Hz for stereo or 274.1 Hz for bilingual.
mode | existing OIRT 6.5 MHz or BG 5.5 MHz sound carrier contains: | 2nd OIRT 6.258 MHz or BG 5.742 MHz carrier contains: | pilot tone in 2nd carrier: |
---|---|---|---|
mono | mono | carrier is absent | none |
stereo | mix of left & right (L+R)/2 | right audio channel | 54.6875 kHz 50% AM with 117.5 Hz |
bilingual | 1st language | 2nd language | 54.6875 kHz 50% AM with 274.1 Hz |
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)/2 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
There is a version of A2 used inSouth Korea,compatible with theSystem 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).
Other names
Zweikanalton is known by a variety of names worldwide. Most commonly used names areZweiton,German Stereo,A2 Stereo,West German StereoandIGR Stereo.
See also
- Multichannel television sound(3 additional audio channels in an NTSC-format audio carrier.)
- NICAM