Onkyo TX-NR646 User Manual page 50

 TV Logic
¼
Suitable for TV shows produced in a TV studio. This mode
enhances the surround effects to the entire sound to give
clarity to voices and create a realistic acoustic image.
 Unplugged
¼
Suitable for acoustic instruments, vocals and jazz. This
mode emphasizes the front stereo image, giving the
impression of being right in front of the stage.
En-18
Using the Listening Modes