Bilingual and stereo sound television programs started being broadcast in Japan in October 1978 using a system developed by NHK Technical Research Labs. This system was modified and standardized by the EIAJ in January 1979.
The original version M TV standard has a monaural FM transmission at 4.5 MHz. For Japanese multichannel television sound a second channel, or sub-channel, is added to the original signal by using an FM sub-carrier at twice the line frequency (Fh, or 15374 Hz). In order to identify the different modes (mono, stereo, or dual sound) a pilot tone is also added on an AM carrier at 3.5 times the line frequency. The pilot tone frequencies are 982.5 Hz for stereo and 922.5 Hz for dual sound. Contrary to Zweikanalton these pilot tones are not coupled to the line frequency but were instead chosen to allow use of filters already employed in the Pocket Bell pager system.1
- ^ Numaguchi, Yasutaka (December 1979). "Present Status of Multichannel-Sound Television Broadcasting in Japan". IEEE Transactions on Broadcasting. BC-25 (4): 128–136. doi:10.1109/TBC.1979.266340.