Hitachi VTUX6430A - Manual (Page 53)

Stereo vs. mono sound
When you select the STEREO option in the initial setup operation, your VCR records in stereo any station that
broadcasts stereo sounds. When a TV channel broadcasts in stereo, you'll see a stereo indicator on the TV
screen.
Set to MONO if the stereo signal is weak and the sound is too "noisy".
Note: When you select MONO, sound is recorded as mono even when a channel broadcasts in stereo.