OPTIMOD SURROUND PROCESSOR INSTALLATION
2-13
E) Set the 2.0 output sample rate to 32, 44.1, 48, 88.2, or 96 kHz.
9. Set surround and 2.0 output levels.
A) L
OCATE to the Set Output Levels screen (SYSTEM SETUP > QUICK SETUP 8).
B) Set the S
URROUND OUTPUT LEVEL control to the desired peak level in units of
dB with reference to digital full-scale. (Note: This control is labeled S
URROUND
OUTPUT 100% in PC Remote.)
–2.0 dBfs is an appropriate value. It provides some headroom for any over-
shoots introduced by equipment (like codecs) following the 8685.
Note that if a given output is fed with a non-limited signal (AGC or LIMIT),
the
peak level will not be controlled tightly.
• IMPORTANT: In MB
LIMIT mode, the 8685’s SURROUND OUTPUT LEVEL and
S
URROUND OUTPUT LEVEL controls do not adjust loudness; they only set the
maximum peak level at the 8685’s output. This is to reduce the likelihood
of setup errors when the 8685 is driving a Dolby Digital channel. The active
D
IALNORM value and the MB LIMITER DRIVE controls set output loudness.
• Regardless of the output mode, do not try to adjust loudness at the re-
ceiver by using the 8685’s O
UTPUT LEVEL controls. Use these controls only to
set output headroom. In MB+L
IMIT mode, use the DIALNORM control to set
loudness. In MB
mode, use the MB LIMITER DRIVE control in the active preset.
In AGC and AGC+L
IMIT modes, use the AGC LIMITER DRIVE control in the ac-
tive preset.
• If you have readjusted any L
IMITER DRIVE control (located in the MULTIBAND
MODIFY screens for the surround and 2.0 processing), you must save the re-
sult as a user preset in order to avoid the possibility of losing your settings,
which will otherwise happen if you recall a different preset.
This will allow you to use the full amount of headroom available in the
transmission channel following the 8685 and, in digital television service,
will minimize or eliminate the need to apply peak limiting to the signal.
This is because the Dolby Digital system allows you to use the D
IALNORM
metadata parameter to ensure that there is enough peak headroom
through the transmission system. For most digital television transmis-
sions, setting D
IALNORM to –24 dB or below (i.e., closer to –31 dB) will en-
sure that no peak limiting ever occurs, assuming that you set loudness
with the 8685’s L
IMITER DRIVE control to make the 8685’s Loudness Level
meter peak at 0 dB with typical dialog and set the 8685’s O
UTPUT control
to –2.0 dBfs, which allows 2 dB of peak headroom for overshoots in the
AC3 codec.
C) Set the 2.0 OUTPUT control to the desired peak level in units of dB with refer-
ence to digital full-scale.
D) Set the A
NALOG OUTPUT control to the desired peak level in units of dBu,
where 0 dBu = 0.775 v r.m.s.
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