Orban OPTIMOD-FM 8500S Operating Manual Download

Page: 91 / 335

OPTIMOD-FM DIGITAL

INSTALLATION

2-35

prevent overshoots in 32 kHz transmission systems, set the 8500S’s

ANDWIDTH

control to 15 kHz.

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

OUD THR

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.

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%

EAK

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

, the Digital Out-

put becomes the "Loudness Reference Output" and the Digital Output

100%

EAK

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% 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%

EAK

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%

EAK

EVEL

control. For example, when the Digital Output 1

100%

EAK

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%

EAK

EVEL

control introduces after the peak limiters. Unless the peak limiters

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

OUDNESS

ONTROL

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%

EAK

EVEL

control is set to 0 dBFS, this arrangement

causes the output loudness to change when you toggle the

BS.1770