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 at 3.5 times the line frequency.