TC Electronic DB6, User Manual

Page: 145 / 174

LM6
DB6 English Manual (2014-10-07) 142
Universal Descriptors
and AC3 Metadata
The “Dialnorm” parameter in AC3 metadata
should indicate the average loudness of a pro-
gram. Basic dynamic range and level control that
rely on this parameter may take place in the con-
sumer’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-ori-
ented, better inter-channel leveling may be ob-
tained with dialnorm permanently set 1 or 2 LU
below the Program Loudness target level.
True-peak meters
The peak meters of LM6 display true-peak as
specified in ITU-R BS.1770. True-peak meters
give a better indication of headroom and risk
of distortion in downstream 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 worksta-
tions and mixers are only sample peak (Final Cut,
Avid, ProTools, Yamaha etc.) and should only be
used as a rough headroom guideline.
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 produc-
tion, 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 bit rate codecs,
-3 dBFS should be considered the limit, while
legacy platforms requiring emphasis may need
even further restriction. As described in EBU
R128, it is 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.