TC Electronic LM2 - Manual (Page 16)

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Loudn. Range
Loudness Range, standardized in EBU R128 and
abbreviated “LRA”, displays the loudness range of a
program, a film or a music track. The unit is LU, which
can be thought of as “dB on the average”.
The Loudness Range descriptor quantifies the variation of
the loudness measurement of a program. It is based on
the statistical distribution of loudness within a programme,
thereby excluding the extremes. Thus, for example, a
single gunshot is not able to bias the LRA number.
EBU R128 does not specify a maximum permitted LRA.
R128 does, however, strongly encourage the use of LRA
to determine if dynamic treatment of an audio signal is
needed and to match the signal with the requirements of
a particular transmission channel or platform.
Consequently, if a program has LRA measured at 10
LU, you would need to move the master fader +- 5 dB to
make loudness stay generally the same over the duration
of the program. (Not that you would want that).
In production, Loudness Range may serve as a guide to
how well balancing has been performed, and if too much
or too little compression has been applied. If a journalist
or video editor isn’t capable of arriving at a suitable LRA,
he could be instructed to call an audio expert for help.
This may be regarded as initial production guidelines:
HDTV and digital radio: Stay below LRA of 20 LU.
SDTV: Stay below LRA of 12 LU.
Mobile TV and car radio: Stay below LRA of 8 LU.
Remember to use LRA the other way around too: If there
is an ideal for a certain genre, check its LRA measure,
and don’t try go below it. LRA should not be used for
Limbo. Allow programs or music tracks the loudness
range they need, but not more than they need.
Loudness Range may also be measured on a broadcast
server to predict if a program is suitable for broadcast
without further processing. LRA is even a fingerprint of a
program and stays the same downstream of production
if no dynamics processing has been applied. You may
even check the number out of a consumer’s set-top box
to verify that distribution processing and Dolby DRC has
been disabled.
Like with Program Loudness and Loudness Max, the
meter should be reset before measuring LRA.
Prog. Loudn.
Program Loudness returns one loudness number for
an entire program, film or music track. Its unit is LUFS.
Some vendors and countries use the unit “LKFS” or
“LFS”, but all three are the same: An absolute measure of
loudness in the digital domain, where the region around
“0” is overly loud and not relevant for measuring anything
but test signals. Expect readings of broadcast programs
in the range between -28 and -20 LUFS.
Program Loudness is used as a production guideline, for
transparent normalizing of programs and commercials,
and to set loudness metadata in delivery if so required.
For delivery or transmission of AC3 format, the metadata
parameter “dialnorm” should reflect Program Loudness.
The easiest way to handle multiple broadcast platforms
is to normalize programs at the station to a certain value,
thereby being able to take advantage of the normalization
benefits across platforms, at the same time enabling
static metadata.
Loudness measurements in LM2 are all rooted in ITU-R
BS.1770-2. However, subtle differences exist between
different regions of the world. Therefore LM2 also
includes the “Loudness Standard” parameter. Be sure to
set this parameter correctly for compliance in your region.
The Program Loudness target is more or less the same
for broadcasters around the world, especially when