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LM5 & LM5D -TDM
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not to measure programs of a shorter duration than approximately 10 seconds, while
the maximum duration may be 24 hours or longer.
Before a new measurement, press the “X” (Reset) key. This resets the descriptors, the
radar and the true-peak meters. Run the audio, and watch the radar and descriptor
fields update accordingly. It is normal that the descriptors wait five seconds into the
program before showing the first readings, while the radar updates instantly. The first
five seconds of a program are included in the descriptor calculations, even though
they are not shown instantly.
LM5D incorporates an intelligent gate, which discriminates between foreground and
background material of a program. Consequently, a measure doesn’t start before audio
has been identified. It also pauses the measurement during periods of only
background noise, and in the fade-out of a music track.
Universal Descriptors and Dolby LM100
Unlike methods that measure dialog only, LM5D may be used with any type of audio –
which includes dialog, of course. If you wish to measure dialog, it’s recommended to
do a manual spot check of a program or a film. Find 10-30 seconds of regular dialog
and measure it with LM5D. Where dialog may be soft, regular or loud, and shift by
more than 15 dB inside a film, regular dialog tends to be less ambiguous and more
consistent across a program.
Note: For compatibility with a proprietary measure such as Dolby LM100, only some
of these meters are updated to use ITU-R BS.1770 and Leq(K) while others are
locked at Leq(A). The software version of LM100 should be 1.3.1.5 or higher in order
for it to comply with BS.1770, and to have its average loudness reading be
compatible with Center of Gravity in LM5. Even used just on speech, Leq(A) is not a
precise approximation to perceived loudness, so please update the unit to BS.1770 to
obtain similar readings and predictable results.
To measure dialog with LM5D in ProTools the same way as Dolby LM100 set to dialog,
also solo the Center channel during a spot check to momentarily disable the channel
weighting specified in BS.1770, if you’re working on a 5.1 stem.
Universal Descriptors and AC3 Metadata
The “Dialnorm” parameter in AC3 metadata should indicate the average loudness of a
program.. Basic dynamic range and level control that rely on this parameter may take
place in the consumer’s receiver. Therefore, its value should not be far off target, or
the results become highly unpredictable.
Center of Gravity in LM5 is directly compatible with Dialnorm in AC3. Most broadcast
stations work against a fixed dialnorm setting, for instance –23 LFS. This would then
be the CoG value to aim a program at. If the program isn’t only dialog, the best
consumer listening results are achieved if you aim Center of Gravity somewhat higher
than the actual goal. For a music program, for instance, the aim should be
approximately 3 LU higher.
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LM5 & LM5D -TDM
Universal Descriptors (LM5D only)
Additional to the short-term loudness (outer ring) and loudness history (radar), LM5D
displays long-term statistical descriptors that describe an entire program, film or
music track. Unlike concepts that measure only dialog, LM5D may measure any type
of audio.
Center of Gravity (CoG) indicates the average loudness of a program, and is directly
operational. If, for instance, a broadcast station is operated at an average loudness
level of –22 LFS, and a commercial has its Center of Gravity measured at –19.5 LFS,
the program should be attenuated by 2.5 dB before transmission for a best fit.
Consistency indicates the loudness variations inside a program. At one extreme, a
steady tone displays a Consistency of 0.0 LU. Broadcast programming typically comes
out with a Consistency between –2 and –5 LU, while classical music or a feature film
can show more negative readings, for instance a Consistency of –10 LU or lower. The
number predicts how much loudness correction in LU (cut and boost) is needed to
have a program or music track played without frequent loudness variations.
Center of Gravity ranges from –80 LFS to +12 LFS, while Consistency ranges from
–40 to 0 LU. Examples of typical Consistency / CoG values:
Cinema movie: -6 to -15 LU / -22 to -30 LFS
Classical music on CD: -5 to -12 LU / -15 to -30 LFS
Broadcast: -2 to -5 LU / -18 to -24 LFS
Commercials: -0.5 to -2 LU / -15 to -22 LFS
Pre 1995 pop/rock CD: -1.5 to -5 LU / -14 to -20 LFS
Hyper-compressed pop/rock CD: -1 to -3 LU / -5 to -8 LFS
Note: If you’re involved with music mastering, please observe that you enter red light
district for CoG values closer to zero than –12 LFS, and that you’re well inside that
zone if you pass the –10 LFS mark. Everything you do to make music even louder will
end up getting counteracted in iTunes or at the broadcast station – but the distortion
you add to go higher will remain.
The same warning may be given for TV commercial production. Don’t aim at max
values, but allow Consistency to go down a bit to let the program breathe. Look at the
radar to put audio focus where you want it to be. When loudness gets normalized,
that’s what will give your message attention.
Universal Descriptors are rooted in Leq(K) as referenced in ITU-R BS.1770, and have
been designed for robustness against moderate gain offsets around normal broadcast
operating levels. If a program exhibits a Consistency of –3.5 LU, and the gain is offset
by 10 dB, its Center of Gravity reading is shifted by 10 dB, while Consistency remains
unchanged. Please find more information about Universal Descriptors in the Tech
Library of the TC website.
Long-term measurements (LM5D only)
Universal descriptors may be used to make program-duration measurements, or you
may “spot-check” regular dialog or individual scenes as required. It is recommended