Hello.
When I was looking at the software
NHK: Rhine River (1981) [DW002-21NH] I had on hand, it was written in Japanese on the back cover.
"
MONO(モノラル、一部ステレオ)"
If you translate this sentence into English, it will be "MONO (monaural sound, partly stereo)".
This notation is only on the back cover, and it is written as "MONO" regardless of the board surface. However, when I play it back, the BGM that flows in some scenes feels like stereo.
When I recorded the voice on a PC and played it while watching the waveform, I noticed that the volume was slightly increased on one side only during BGM playback. The volume on the right side often increased, but sometimes the volume increased only on the left side.
However, the volume of the sound of the narration and the video shot on site will be constant.
This probably means that the jacket is correct and some of the audio is recorded in stereo.
However, the reason why this back cover was labeled "MONO (monaural sound, partly stereo)" is unknown.
No one now knows why the distributor, Laserdisc Corporation, did not recognize the software as fully stereo.