TC Electronic LM2 Plug-in - Manual (Page 10)

10 / LM6 Radar Loudness Meter
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 LM6/LM2. 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.
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 or Program Loudness
in LM6. 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 LM6 the same way Dolby LM100 is sometimes used, 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 Meta-data
The “Dialnorm” parameter in AC3 meta-data 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 consumer results become highly unpredictable.
Program Loudness in LM6 is directly compatible with Dialnorm in AC3. Most
broadcast stations work with a fixed dialnorm setting, for instance –23 LUFS. This
would be the Program Loudness target level for any program.
If your station is more music than speech, better inter- channel leveling may be
obtained with dialnorm permanently set 1 or 2 LU lower than the Program Loudness
target level.
True-peak meters
The peak meters of LM6/LM2 display true-peak as specified in ITU-R BS.1770.
True-peak meters give a better indication of headroom and risk of distortion in
dowstream equipment such as sample rate converters, data reduction systems and
consumer electronics than digital sample meters used e.g. in CD mastering. Note that
the standard level meters in most digital workstations and mixers are only sample
peak (Final Cut, Avid, ProTools, Yamaha etc.), and should only be used as a rough
guideline of the headroom.
Note that the meter scale is extended above 0 dBFS. Most consumer equipment
distorts if you see readings above 0. It’s not a problem to have true-peak level going
to -1 dBFS in production, but legacy platforms (analog, NICAM etc.) and some
data-reduction codecs may distort unless true-peak level is kept lower. With Dolby
AC3 and with low bitrate codecs, -3 dBFS should be considered the limit, while
legacy platforms requiring emphasis may need even further restriction. Like described
in EBU R128, it’s recommended to make full use of the headroom with true-peaks
going to -1 dBFS in production, and to only restrict peak level further during
distribution/transmission.