TC Electronic Radar Meter Bundle TDM - Manual (Page 10)

ENGLISH
8 / LM5/LM5D & AM6
ENGLISH
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 secs 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.
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 consumer results become highly unpredictable.
Program Loudness in LM5 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 LM5 display true-peak as specified in ITU-R BS.1770-2.
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.