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 stereo. Unlike the competing NICAM standard, Zweikanalton is an analog system.
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.
Technical details
A 2nd FM sound carrier containing a second sound channel is transmitted at a frequency 242kHz higher than the default FM sound carrier, and contains a 54.6875kHz pilot tone to indicate whether the broadcast is mono, stereo or bilingual.
This pilot tone is 50% amplitude-modulated with 117.5Hz for stereo or 274.1Hz for bilingual. The absence of this carrier indicates normal mono sound.
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.
Carrier frequencies are chosen so 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 15625Hz = 242187.5Hz) 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 (54687.5Hz). The modulated tone frequency is 117.50Hz for stereo transmission and 274.1Hz for bilingual transmission. Absence of this tone is interpreted as a monaural transmission.
There is a modified version of Zweikanalton used in South Korea, compatible with the NTSC System M standard of TV transmission. In this case the second FM carrier is 14.25 times the line frequency, or about 224kHz, above the first carrier; pre-emphasis is 75 microseconds; the stereo pilot tone frequency is 149.9Hz; the bilingual pilot tone frequency is 276Hz; and the second channel carries L-R (not R).
History
Zweikanalton was developed by the Institut für Rundfunktechnik (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 subsequently introduced Zweikanalton on its Das Erste channel on 29 August 1985 in honour of the 1985 edition of the Internationale Funkausstellung Berlin (IFA). West Germany thus became the first country in Europe to use multiplexed sound on its television channels.
In Malaysia, TV3 used Zweikanalton on its UHF analogue transmission frequency (Channel 29), while NICAM was instead used on its VHF analogue transmission frequency (Channel 12).
In Indonesia, the first TV station to use Zweikanalton was SCTV, which utilized from its start of broadcasting in 1990. Later, Zweikanalton was abandoned by national networks in favor of NICAM but at least there was one local television station that still used Zweikanalton.
As a result of the analogue television switch-off in most countries which used Zweikanalton, 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 (Europe and Asia-Pacific), and Dolby Digital AC-3 on ATSC in 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.
↑ 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
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