|
Zweikanalton ("two channel sound") or A2 Stereo,〔(Stereo sound systems - QSL.net )〕 is a television sound transmission system used in Germany, Austria, Switzerland, and other countries that use or used PAL-B or PAL-G. South Korea formerly utilised its variant of this format in analogue television system until 31 December 2012. It relies on two separate FM carriers. 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. == How It Works == A 2nd FM sound carrier containing the right channel for stereo is transmitted at a frequency 242 kHz higher than the existing mono FM 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. 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 the signal-to-noise ratio by 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 of intermodulation products 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Zweikanalton」の詳細全文を読む スポンサード リンク
|