LMn Manual

Interface and feature reference
LM2n / LM6n Manual 19
Sliding Loudness descriptor
Sliding Loudness – unlike Program Loudness,
Loudness Range and Loudness Max – is a con-
tinuously updated measure that doesn’t need
to be reset. This type of descriptor is especial-
ly 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 Slid-
ing Loudness as the other displays simultaneous
information about the full program side by side
with the most recent loudness history.
Because the Sliding Loudness measurement
is completely ungated, it may also be used to
spot-check sections of a program complying
to “raw” ITU-R BS.1770 and the first revision of
ATSC A/85.
LM2n/ LM6n makes use of optimized statistics
processing in order to display a sliding loudness
value (a prognosis) as quickly as possible after
a reset.
Loudness Range (LRA) descriptor
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 av-
erage”.
The Loudness Range descriptor quantifies the
variation of the loudness measurement of a pro-
gram. It is based on the statistical distribution
of loudness within a program, thereby excluding
the extremes. Thus, for example, a single gun-
shot is not able to bias the LRA number.
EBU R128 does not specify a maximum permit-
ted LRA. R128 does, however, strongly encour-
age the use of LRA to determine if dynamic treat-
ment 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 per-
formed, and if too much or too little compres-
sion 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.
The following may be regarded as initial produc-
tion 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 suit-
able for broadcast without further processing.
LRA is even a fingerprint of a program and stays
the same downstream of production if no dy-
namics 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.
As with Program Loudness and Loudness Max,
the meter should be reset before measuring
LRA.