Two-channel sound

The two-channel , two-tone or A2 process is an analog technology for sound transmission in analog cable and analog terrestrial television , in which two independent audio channels are transmitted. The two channels can either be used for two-channel stereophony , for the transmission of versions in different languages (e.g. of the original and the synchronized version of a foreign film ) or for the transmission of the normal version for people with normal vision and the audio version for the blind and visually impaired (two-channel Tone) can be used. If two versions are transmitted, only mono operation is possible, as only two audio channels are available.

technology

In contrast to the traditional mono sound with analog terrestrial or cable transmission from television stations in German-speaking countries ( television standard PAL -B / G), which is transmitted frequency-modulated on a sound carrier at 5.5 MHz in the baseband , an additional sound carrier is used with the two-channel sound method 5.7421875 MHz used. This second sound carrier is 20 dB weaker than the picture carrier and 7 dB weaker than the traditional sound carrier at 5.5 MHz in order not to cause any interference in the picture. For the same reason it has a distance of 15.5 times the line frequency from the other sound carrier, i.e. it is exactly between two harmonics .

compatibility

There are two modes of transmission that place different requirements on compatibility: stereo sound, where a mono receiver should receive a composite signal as a mono signal, and two-channel transmission, where a mono receiver should only receive the first sound channel. In stereo transmission, the traditional sound carrier is modulated with the sum signal (L + R) and the second sound carrier is only modulated with the R signal; Mono TV sets that only evaluate the first sound carrier play back a mixture of both channels, as required, while stereo TV sets can reconstruct the left channel by forming the difference. In the case of two-channel transmission, the main channel is modulated with the main language or the normal version and the secondary channel is modulated with the second language or the audio film version, so mono televisions only play the main language. To identify and differentiate between the two modes, a pilot tone of 54.6875 kHz (3.5 times the line frequency of 15.625 kHz) is transmitted in the secondary channel (5.74 MHz), amplitude-modulated with 274 Hz (two-channel) or 117 Hz (stereo) .

Reconstruction of the left channel with stereophonic transmission:

{\ displaystyle L = \ left (L + R \ right) -R}

Variant for standard M

A variant of the two-channel tone process is used in South Korea for the local standard M with NTSC color. With NTSC-M, the main sound carrier is at 4.5 MHz, the second sound carrier at 14.25 times the line frequency, i.e. approx. 4.724 MHz with a pre-emphasis of 75 microseconds. The pilot tones for identifying the type of transmission are 149.9 Hz for stereo and 276 Hz for bilingual broadcasts. Another difference to the B / G variant is that the second sound carrier in stereo mode is modulated with the difference L − R (instead of R as in the B / G method). South Korea thus deviates from the MTS multi-channel sound method that is otherwise common for the M standard .

distribution

The two-channel tone or A2 method is used in the B / G variant in Germany, Austria , Switzerland and the Netherlands for analogue terrestrial and cable transmission, and in South Korea in the M variant.

history

The German two-channel sound system was developed by the IRT . It was introduced by ZDF on September 13, 1981 . The Federal Republic was thus the first country in Europe with multi-channel sound on television. The ZDF broadcasting chain was then gradually expanded, which is why initially not the entire broadcasting area was able to receive multi-channel broadcasts. To make the new technology more palatable to the public, a 30-minute commercial was broadcast daily between 2:00 p.m. and 4:00 p.m. The first introduced the two-channel sound on August 29, 1985 on the occasion of the 1985 International Radio Exhibition .

The end of the era of analog television transmission naturally also includes the end of analog (two-channel) sound transmission.

Different standards for multichannel sound in terrestrial television

NICAM

In most other countries with European standards of 625 lines / 25 frames per second, the digital NICAM 728 method is used for stereo and two-channel sound transmission in analog television . It was developed in the UK by the BBC . With NICAM, the analogue sound is broadcast in parallel in mono in order to create compatibility with mono receivers.

MTS

A third variant is the MTS method , which is particularly widespread together with the M NTSC standard .

Multi-channel sound with other distribution channels

Like NICAM and MTS, the two-channel sound process is only used for terrestrial analog TV transmission and for analog cable channels.

Analog satellite television

In the case of analog satellite transmission, because of the much larger frequency range, there were more than two audio sub-carriers available per television station, which could be selected by programming the receiver. Thus it was also possible to transmit original films in stereophony or several different languages were recorded in two or more channels. The other sound sub-carriers beyond the second were often used for radio programs. Examples of these techniques were, on the one hand, the station Das Erste , which transmitted its own stereo sound via ASTRA analog on the first two sound carriers at 7.02 MHz and 7.20 MHz and additionally the 7.38 MHz and 7.56 MHz on the sub-carriers Radio station SWR3 broadcast in stereo. The broadcasters ARTE and Eurosport broadcast the same sound with foreign-language commentators on the respective sound carriers.

Digital television

In digital television , stereo and two-channel sound is also realized digitally. In 2005 , either the MPEG-2 process with the sound in MPEG-1 Layer 2 or the Dolby Digital process, which also supports multi-channel content up to DD7.1 allows. But there are also DVB-S transmitters that broadcast both variants (MPEG-Audio, Dolby-Digital) in parallel.

DVB-T

With DVB-T (Das Erste and BR) there are problems with the two-channel sound. In order to give old receivers the opportunity to receive two-channel sound, Das Erste broadcasts not conforming to DVB-T specifications. The sound is sent on the left or right stereo channel. This means that it is not possible to select the channel with modern DVB-T receivers that expect two-channel coding. However, televisions usually offer the option of reproducing only the left or only the right sound track.

Individual evidence

^ ZDF / The company / History. Retrieved April 1, 2010 .
↑ www.wunschliste.de ( Memento of the original from August 29, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. We switch to "Episode 10:" You are not David! - The legendary multi-channel audio test broadcast @1@ 2
↑ 50 years of ARD. Retrieved April 1, 2010 .

[1] ZDF / The company / History. Retrieved April 1, 2010 .

[Zweikanalton-2] www.wunschliste.de ( Memento of the original from August 29, 2011 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. We switch to "Episode 10:" You are not David! - The legendary multi-channel audio test broadcast @1@ 2

[3] 50 years of ARD. Retrieved April 1, 2010 .