TC Electronic SYSTEM 6000 MKII Algorithm Manual - Lm6
114
lM6
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Descriptor 1-2
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 program, 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 “LUFS”, 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 LM6 are all rooted in ITU-R
BS.1770. However, subtle differences exist between
different regions of the world. Therefore LM6 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 taking the
measurement differences into account. Target numbers
range between -24 and -22 LUFS.
Like with Loudness Range and Loudness Max, the meter
should be reset before measuring Program Loudness.
Sliding Loudn.
Sliding Loudness, unlike Program Loudness, Loudness
Range and Loudness Max, is a continuously updated
measure that doesn’t need to be reset. This type of
descriptor is especially useful when “mixing by numbers”,
i.e. when there is no access to the extremely informative
radar display. When mixing by numbers, having Program
Loudness as one descriptor and Sliding Loudness as the
other displays simultaneous information about the full
program side by side with the most recent loudness history.