Yamaha DSP-A3090 Mode D'emploi page 12

Dolby Pro Logic + 2 Digital Sound Fields
A digital sound field is created on the presence side and the rear
surround side of the Dolby Pro Logic Surround-processed sound
field individually. They create a wide acoustic environment and
emphasize surround-effect in the room, letting you feel much
presence as if you are watching a movie in a popular Dolby Stereo
theater.
This combination is used on sound field programs No. 7
through No. 11, and "PROLOGIC/Enhanced" of No. 12.
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Dolby Surround AC-3 + 3 Digital Sound Fields
A digital sound field is created on the presence side and the
independent left and right surround sides of the Dolby Surround AC-
3-processed sound field individually. They create a wide acoustic
environment and much surround effect in the room without losing
high channel separation. With wide dynamic range of AC-3 sound,
this sound field combination lets you feel as if you are watching a
movie in the newest Dolby Stereo Digital theater. This will be the
most ideal home theater sound at the present time.
This combination is available on the sound field programs No. 7
through No. 11 and "AC-3/Enhanced" of No. 12 when playing a
source with the Dolby Surround AC-3 decoded.