Orban OPTIMOD-FM 8700, Operating Manual

Page: 95 / 390

OPTIMOD-FM DIGITAL INSTALLATION
2-33
To facilitate error-free loudness calibration through your transmission
system, activating the BS.1770 Safety Limiter changes the behavior of the
Digital Output
100% P
EAK
L
EVEL
control. Normally, changing the setting
of this control changes both the loudness and peak level of the signal
appearing at the Digital Output driving your digital radio transmitter.
However, when the BS.1770 Safety Limiter is turned
ON , the Digital Out-
put becomes the "Loudness Reference Output" and the Digital Output
100% P
EAK
L
EVEL
control sets only the peak level, not the loudness . In this
case, the output loudness is always calibrated correctly with respect to
0 dBFS.
(Note: If both Digital Output 1 and Digital Output 2 are sourced from
“HD,” then Digital Output 2 becomes the “Loudness Reference Output”
instead of Digital Output 1.)
For example, setting the Digital Output 1
100% P
EAK
L
EVEL
control to
–3 dBFS always constrains the maximum peak level appearing at Digital
Output 1 to –3 dBFS, but changing the setting of the Digital Output 1
100% P
EAK
L
EVEL
control does not change loudness. This is because when
the BS.1770 Safety Limiter is turned ON, a second “hidden” gain control
is inserted before the input of the peak limiter. The gain set by the “hid-
den” control complements the setting of the Digital Output 1
100% P
EAK
L
EVEL
control. For example, when the Digital Output 1
100% P
EAK
L
EVEL
control is set to –3 dBFS, the “hidden” control adds 3 dB of gain before
the peak limiters to compensate for the 3 dB of loss that the
100% P
EAK
L
EVEL
control introduces after the peak limiters. Unless the peak limiters
produce gain reduction, this arrangement keeps the overall gain constant
from the input of the peak limiter to the Digital Output.
If the peak limiters produce enough gain reduction to reduce loudness
audibly, this gain reduction will cause the output loudness to be lower
than the setting of the
BS.1770 L
OUDNESS
C
ONTROL
T
HRESHOLD
. This will
never occur with BS.1770 reference levels normally used in digital radio
(–18 LUFS) and digital television (–23 LUFS or –24 LUFS) because with
these reference levels, any peak limiting that occurs will be too brief to
audibly affect loudness.
Unless the
100% P
EAK
L
EVEL
control is set to 0 dBFS, this arrangement
causes the output loudness to change when you toggle the BS.1770
S
AFETY
L
IMITER
control ON and OFF. In our example, the loudness will de-
crease by 3 dB when you set the BS. 1770 S
AFETY
L
IMITER
to OFF .
E) After you have chosen a Processing Preset and adjusted it to your taste (step
22 on page 2-41, you must set the preset’s
HD F
INAL
L
IMITER
D
RIVE
to create the
appropriate amount of gain reduction in the BS.1770 Safety Limiter. Then
save the result as a User Preset. We recommend allowing the BS.1770 Safety
Limiter to produce no more than 3 dB of gain reduction.
11. Set output and configuration level.
A) Navigate to the
I
NPUT
/
OUTPUT
> O
UTPUT
1
screen.
You can use either program material or tone to set your output level
(and thus, your on-air modulation). If you want to use tone, turn the
400Hz calibration tone on.
B) Set the A
NALOG
O
UT
S
OURCE
to FM or FM+D
ELAY
, depending on whether you
need to apply diversity delay to that source. See Diversity Delay on page 2-77.