Orban OPTIMOD-FM 8700, Operating Manual

Page: 55 / 390

OPTIMOD-FM DIGITAL INTRODUCTION
1-25
The loudness meter indicates both BS.1770 Short-Term and Integrated Loudness on
the same scale. The solid bar indicates the Integrated Loudness, while the floating
bar segment indicates the Short-Term Loudness. Per the BS.1770-3 specification, the
integration time of the Short-Term Meter is always 3 seconds, while the Integrated
Meter uses silence gating and its integration time is 10 seconds. Because the meter is
always monitoring program material, it integrates the previous 10 seconds of pro-
gram material and weights all program material equally within the specified time
window. For example, material occurring 3 seconds in the past and 8 seconds in the
past both contribute equally to the meter’s current indication; newer program ma-
terial in the specified time window is not favored over older program material.
Because loudness perception combines the contributions of all acoustic sources,
there is only one Loudness Level meter indication for both stereo channels.
The unit of measure in the BS.1770 meter is LKFS or LUFS, which are the same, dif-
fering only in nomenclature. A change of 1 LUFS is the same as a change of 1 dB.
In the digital radio chain, “LKFS” and “LUFS” are absolute loudness measurements
with respect to digital full scale. “LK” and “LU” (without the “FS”) are relative loud-
ness measurements, where “0” on the meter corresponds to a user-preset “BS.1770
Reference Level,” which you set via your Optimod’s
BS.1770 L
OUDNESS
C
ONTROL
T
HRESHOLD
control. The BS.1770 meter on your Optimod indicates “LK” or “LU”; you
can choose which label to use via a control available on the HD D
IGITAL
R
ADIO
tab in
I/O
SETUP
. The other BS.1770-associated controls for digital radio are also there.
The meter is scaled so that the loudness level at the consumer’s receiver is correct
when the 8700i’s digital radio processing chain is adjusted to make the dominant
program material indicate “0 dB” on the 8700i’s Loudness Level meter and the
BS.1770 R
EFERENCE
L
EVEL
(which you must enter manually) in I/O S
ETUP
> HD R
ADIO
is equal to that specified by the regulatory authority in your country.
In the analog radio processing chain, the BS.1770 meter and Safety Limiter are cali-
brated per EBU Tech 3344
4
, Section 5.9. This calls for a 1 kHz sinewave at –23 LUFS to
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
preemphasis. The loudness meter is calibrated so that “0” corresponds to the setting
of the
BS.1770
LOUDNESS
C
ONTROL
T
HRESHOLD
control in I
NPUT
/O
UTPUT
> U
TILITY
.
Built-in Calibrated Line-up Tones
To facilitate matching the output level of the 8700i to the transmission system that
it is driving, the 8700i contains an adjustable test tone oscillator that produces sine
waves at 8700i’s (analog or digital) left, right, and composite outputs. The frequency
and modulation level of the line-up tones can be adjusted from the front panel (as
described on page 3-88).
4
EBU – TECH 3344: “Practical guidelines for distribution systems in accordance with
EBU R 128; Supplementary information for EBU R 128,” available for free download.
Use a search engine to find the latest version.