Orban OPTIMOD-FM 8700, Operating Manual

Page: 88 / 390

2-26
INSTALLATION ORBAN MODEL 8700i
teners
1
. We suggest using a maximum of 3 dB gain reduction in the BS.1770 safe-
ty limiter.
A) Navigate to the
I
NPUT
/
OUTPUT
> U
TILITIES
screen.
B) Turn the
1770 S
AFETY
L
IMITER
control
O
N
.
C) Set the
1770 L
OUDNESS
T
HRESH
control to the target loudness specified by your
country’s governing authority. EBU B 128 specifies –23 LUFS.
The BS.1770 Loudness Meter is calibrated in relative units (LU) so that it
indicates “0” when the loudness is equal to the target loudness set by the
1770 L
OUDNESS
T
HRESH
control. In an overshoot-free transmission system,
a 1 kHz sinewave at –23 LUFS must produce an FM carrier deviation of
±
10 kHz without pilot tone. This corresponds to 13.33% modulation
without pilot tone. This calibration includes 50
µ
s transmission preempha-
sis.
Note for version 1.0 software: We have found that with typical pop music,
a –23 LUFS setting typically produces about –5 dB BS.412 MPX Power and
rarely produces ±75 kHz peak carrier deviation. 0dB MPX power is not
reached unless the
BS.1770 T
HRESHOLD
control is set to approximately –17
LUFS. This behavior seems odd (the low modulation level significantly
compromises the received S/N ratio in weak signal areas and in moving
vehicles), so we are unsure if our interpretation of EBU Tech 3344 is cor-
rect in this initial release and we welcome any feedback. Please email
Bob Orban at the address shown at
http://www.orban.com/contact/ if you
discover an error in our calibration.
D) The calibration of the
1770 L
OUDNESS
T
HRESH
control is correct if the transmit-
ter’s modulation level was calibrated using your Optimod’s built-in lineup
tone (step 8 on page 2-22). If you turned down the drive level to the FM
transmitter (via the
C
OMPOSITE
O
UT
, DO 100%,
or
AO 100%
controls depending
on how you are driving your transmitter) to compensate for overshoots in the
signal path following the Optimod, turn the
1770 L
OUDNESS
T
HRESH
control up
by the same amount that you turned the output level control down. This will
preserve correct loudness at the receiver.
For example, assume that you turned down the output level control by
2 dB compared to its calibration using your Optimod’s tone generator, so
that a line-up tone that would produce
±
75 kHz deviation in an over-
shoot-free transmission system instead produces ± 59.6 kHz deviation to
allow for 2 dB of overshoot with program material. In this case, set the
1770 L
OUDNESS
T
HRESH
control to –21 LUFS instead of –23 LUFS.
E) If you have not already done so in step 12 on page 2-24, activate the MPX
Power Controller by setting it to some setting other than
O
FF
. This is necessary
to enable the
M
ULTIPLEX
P
OWER
O
FFSET
control.
1
See Begnert, Fabian; Ekman, Håkan; Berg, Jan, “Difference between the EBU R-128
Meter Recommendation and Human Subjective Loudness Perception,” AES Conven-
tion Paper 8489, 131
st
AES Convention, (October 2011). This paper states, “These
loudness-equalized signals gave rise to a perceived maximum loudness difference of
2.8 dB.”