Orban OPTIMOD-FM 8500S Operating Manual page 91

OPTIMOD-FM DIGITAL
prevent overshoots in 32 kHz transmission systems, set the 8500S's HD
B
ANDWIDTH
12. Set up and activate the BS.1770 Safety Limiter (optional).
The BS.1770 Safety Limiter applies only to the digital radio processing. It prevents
the BS.1770-3 integrated loudness from exceeding a value set by the L
control. If your country requires that the integrated loudness of your digital ra-
dio broadcast to be constrained according to the BS.1770-3 loudness measure-
ment algorithm, execute the steps below. If your country does not require this,
leave the BS.1770 Safety Limiter off. It must be OFF if you are transmitting HD
Radio.
A) To use the BS.1770 Safety Limiter, assign the output source of one of the Digi-
tal Outputs to HD. See step (11.I) on page 2-33. We suggest using Digital Out-
put 1 to drive the digital radio transmitter.
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
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
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% PEAK LEVEL 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
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
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
L
EVEL
produce gain reduction, this arrangement keeps the overall gain con-
stant 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
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
causes the output loudness to change when you toggle the BS.1770
control to 15 kHz.
L
EAK EVEL
L control sets only the peak level, not the loudness. In this
EAK EVEL
control does not change loudness. This is because when
L
EAK EVEL
control. For example, when the Digital Output 1 100% P
control introduces after the peak limiters. Unless the peak limiters
L
EAK EVEL
control. Normally, changing the setting
C T
OUDNESS ONTROL
control is set to 0 dBFS, this arrangement
INSTALLATION
OUD THR
EAK
L
EAK EVEL
EAK
. This will
HRESHOLD
2-35