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Zweikanalton ("two channel sound", A2 Stereo) is a television
Television

Television is a widely used telecommunication mass-media for transmitting and receiving moving , either monochrome or color, usually accompanied by sound....
 sound transmission system used in Germany
Germany

Germany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium, and the Netherlands....
 and other countries. It relies on two separate FM carriers
Carrier wave

In telecommunications, a carrier wave, or carrier is a waveform that is Modulation with an signal for the purpose of conveying information....
. This offers relatively high separation between the channels (compared to a subcarrier
Subcarrier

A subcarrier is a separate analog or digital signal carried on a main radio transmission , which carries extra information such as voice or data....
-based multiplex
Multiplexing

In telecommunications and computer networks, multiplexing is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium....
 system) and can thus be used for bilingual broadcasts as well as stereo
Stereophonic sound

Stereophonic sound, commonly called stereo, is the reproduction of sound, using two or more independent Sound recording and reproduction channels, through a symmetrical configuration of loudspeakers, in such a way as to create a pleasant and natural impression of sound heard from various directions, as in natural hearing....
.

second FM carrier is transmitted on a frequency 242 kHz higher than the main FM carrier.






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Zweikanalton ("two channel sound", A2 Stereo) is a television
Television

Television is a widely used telecommunication mass-media for transmitting and receiving moving , either monochrome or color, usually accompanied by sound....
 sound transmission system used in Germany
Germany

Germany , officially the Federal Republic of Germany , is a country in Central Europe. It is bordered to the north by the North Sea, Denmark, and the Baltic Sea; to the east by Poland and the Czech Republic; to the south by Austria and Switzerland; and to the west by France, Luxembourg, Belgium, and the Netherlands....
 and other countries. It relies on two separate FM carriers
Carrier wave

In telecommunications, a carrier wave, or carrier is a waveform that is Modulation with an signal for the purpose of conveying information....
. This offers relatively high separation between the channels (compared to a subcarrier
Subcarrier

A subcarrier is a separate analog or digital signal carried on a main radio transmission , which carries extra information such as voice or data....
-based multiplex
Multiplexing

In telecommunications and computer networks, multiplexing is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium....
 system) and can thus be used for bilingual broadcasts as well as stereo
Stereophonic sound

Stereophonic sound, commonly called stereo, is the reproduction of sound, using two or more independent Sound recording and reproduction channels, through a symmetrical configuration of loudspeakers, in such a way as to create a pleasant and natural impression of sound heard from various directions, as in natural hearing....
.

How it works

The second FM carrier is transmitted on a frequency 242 kHz higher than the main FM carrier. This frequency is 15.5 (15.5 x 15625Hz = 242187,5 Hz) times the line frequency, which reduces interference with the video signal. It can carry either a completely separate audio program, or be used for stereo sound transmission. In the latter case, the first FM carrier carries L+R for compatibility, while the second carrier carries 2*R (not L-R.)

After combining the two channels, this method improves Signal-to-noise ratio
Signal-to-noise ratio

Signal-to-noise ratio is an electrical engineering measurement, also used in other fields , defined as the ratio of a signal power to the noise power corrupting the signal....
 by reducing the correlated noise between the channels. The second carrier also contains a control tone to indicate whether the transmission is stereo or dual sound. This control tone is a 50% AM modulated tone. The carrier frequency is 3.5 times line frequency (54687.5 Hz) and the modulated tone frequency is 117.5 Hz for stereo transmission and 274.1 Hz for dual sound. Absence of this tone is interpreted as a monaural transmission.

System M variant

There is a version of A2 used in Korea, compatible with the M standard 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 control frequency is 149.9 Hz; the dual sound control 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 are German Stereo, A2 Stereo, West German Stereo and IGR Stereo.

See also

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    Multichannel television sound

    Multichannel television sound, better known as MTS , is the method of encoder three additional channel of Sound into an NTSC-format Sound carrier wave....
  • NICAM
    NICAM

    NICAM stands for Near Instantaneous Companded Audio Multiplex. It is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks....