Optimod-Surround 8685 V1.0 Operating Manual - Orban

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INSTALLATION ORBAN MODEL 8685
The 8685’s two analog output channels are most commonly used for
monitoring. Nevertheless, they produce low overshoot and can be used
to drive a transmission system with an analog input.
10. Set surround and 2.0 global Dialnorm values. (Do not skip this step!)
If you skip this step, your audio may be objectionably louder or quieter than
other stations’ audio.
The 8685 is designed to work smoothly with Dolby Digital. In essence, the Dolby
Digital Dialnorm metadata sets an invisible volume control that is cascaded with
the volume control in the consumer’s receiver. To produce the same loudness as
other properly set up transmission channels, the 8685 needs to be aware of the
Dialnorm value you are transmitting to the consumer. The 8685 uses this value in
two ways:
• It adjusts the sensitivity of the 8685’s Loudness Level meters so that when the
Loudness Level meters are peaking at 0 dB on speech material, loudness is correct
at the receiver. This means that you can use the 8685’s Loudness Level
meter as a reference if you are modifying a factory preset and want to ensure
correct loudness at the consumer’s receiver.
• It scales the output level of the 8685’s presets so that the level will be correct
for the Dialnorm value you are transmitting to the consumer. To do this, it
sets the gain of a hidden level control cascaded with the 8685’s LIMITER DRIVE
control. This gain adjustment is before the 8685’s look-ahead limiters and
OUTPUT 100% controls. This arrangement allows you to use the full headroom
of the Dolby Digital transmission channel regardless of the Dialnorm setting.
In addition, changing Dialnorm adds a hidden offset to the LOUDNESS
THRESHOLD control’s displayed setting, which ensures that the loudness controller’s
gain reduction does not change when DIALNORM is changed.
These scale factors adjust themselves automatically so that the loudness
of the consumer’s receiver is the same regardless of the settings of the
8685’s SURROUND OUTPUT 100% and 2.0 OUTPUT 100% controls, whose only
purpose is to set the 8685’s maximum peak output level with respect to
0 dBfs. This allows you to compensate for transmission channels that introduce
peak overshoots.
For example, if you change the SURROUND OUTPUT 100% control from
0 dBfs to –6 dBfs, the drive level into the look-ahead limiters automatically
increases by 6 dB. Meanwhile, the threshold of the loudness controller
and the sensitivity of the 8685’s Loudness Level meter decrease by 6
dB. Hence, the r.m.s. drive level into the Dolby Digital encoder stays the
same, the loudness controller produces the same amount of gain reduction,
and the Loudness Level meter continues to peak at 0 dB.
To change the 8685’s output loudness, adjust its DIALNORM value or adjust
the MB LIMITER DRIVE control in the active processing preset. Adjusting
DIALNORM changes loudness without changing the indication on the
8685’s Loudness Level meter and without changing the amount of gain
reduction in the loudness controller. Adjusting MB LIMITER DRIVE changes
both the Loudness Level meter’s indication and the amount of gain reduction
in the loudness controller.