Optimod-Surround 8685 V1.0 Operating Manual - Orban

2-30
INSTALLATION ORBAN MODEL 8685
If it is impossible to delay the video, set the OUTPUT DELAY control to
MINIMUM. This will produce approximately 20 ms of delay, which is low
enough not to cause detectable AV sync problems.
10. Set the 2.0 processing’s output level if OUTPUT PREEMPHASIS control is set
Flat.
[Skip this step if the OUTPUT PREEMPHASIS control is set to 50μs or 75μs.]
LOCATE to INPUT/OUTPUT > 2.0 OUT > 2.0 OUTPUT LEVEL (100%) and set the 2.0
OUTPUT LEVEL (100%) control to desired peak level in units of dBfs (dB with respect
to digital full scale). The setting of the 2.0 OUTPUT 100% control is the
maximum peak level that the 8685 can produce at its output. This level corresponds
to a reading of 0 dB on the 8685’S 2.0 OUTPUT METER.
Typical settings are –0.5 dBfs to –3.0 dBfs, depending on whether sample
rate conversion and/or lossy encoding is occurring downstream from the
8685. Refer to Setting Output/Modulation Levels on page 1-21.
• If the 2.0 OUTPUT SOURCE is AGC+LIMIT or MB+LIMIT (step (9.G) on page 2-28),
the 8685’s look-ahead limiter will automatically constrain the peak output
level to the setting of the 2.0 OUTPUT 100% control without clipping.
• If and only if the 2.0 OUTPUT SOURCE is MB+LIMIT, the average level and loudness
do not change when you adjust the 2.0 OUTPUT Level (100%) control. The
control only sets the maximum peak level at the 8685’s output. For every dB
that the 2.0 OUTPUT SOURCE is turned down, the 8685 automatically increases
the limiter drive by 1 dB to compensate. This is to ensure that the output
loudness is always consistent with the 8685’s active DIALNORM setting.
• If the 2.0 OUTPUT SOURCE is AGC or MB, the 8685’s output level is not peak
limited. However, its average value is usually well controlled by the 8685’s
multiband compressor and loudness controller. The 8685’s peak output level
will depend on the peak-to-average ratio of the program material, so clipping
is possible if the 2.0 LIMITER DRIVE control in the active preset is set too high.
It is normal for the 2.0 OUTPUT LEVEL meter to indicate 0 dB on peaks
when the 2.0 OUTPUT SOURCE is AGC+LIMIT or MB+LIMIT. This does not indicate
clipping; the look-ahead limiter is constraining peaks to this level.
The only reason to choose the AGC or MB output sources is to minimize
input/output delay, which is important if you are driving talent headphones
from the 8685’s output. Otherwise, AGC+LIMIT and MB+LIMIT are
preferred because the 8685’s look-ahead limiter prevents clipping in
normal operation.
To prevent objectionable clipping distortion when the 2.0 OUTPUT SOURCE
is AGC or MB, set the 2.0 LIMITER DRIVE control as follows:
a) Make sure that the program material is loud enough to produce normal
amounts of gain reduction in the AGC (if activated), the multiband
compressor/limiter, and the loudness controller (if activated).
b) If the 8685’s 2.0 OUTPUT LEVEL meter is frequently hitting the top of its scale
(0 dB) and the 8685’s look-ahead limiter is defeated (as it is when the 2.0