Sony STR-DE598 Operating Instructions Manual page 29

M Playback channel indicators: The letters
(L, C, R, etc.) indicate the channels being
played back. The boxes around the letters vary
to show how the receiver downmixes the
source sound (based on the speakers settings).
L (Front Left), R (Front Right), C (Center
(monaural)), SL (Surround Left), SR
(Surround Right), S (Surround (monaural or
the surround components obtained by Pro
Logic processing)), SB (Surround Back (the
surround back components obtained by 6.1
channel decoding))
Example:
Recording format (Front /Surround): 3/2
Output channel: When the surround speakers size
parameter is set to "NO"
Sound Field: A.F.D. AUTO
L C R
SL SR
29 GB