Algorithm Manual Revision 4

ALC 6
English Manual – Updated 2018-02-28 173
ALC6 used for Transmission
1. Load a suitable ALC6 preset, then follow
these directions in the given order.
2 a. If programs have already been normalized
to Target level before arriving at the proces-
sor, set the Pre Process parameter to “Nor-
malized”.
2 b. If many programs have not been normalized
to Target level before arriving at the proces-
sor, set the Pre Process parameter to “Not
Norm” or to “Universal”. After measuring
typical programs at the ALC6 input using a
LM6 loudness meter, adjust Input Level.
For example, if regular programs measure
-24.3 LUFS and the Target level is -23 LUFS,
dial in +1.3 dB as Input Level. Note how In-
put Gain may need adjustment once in a
while as content becomes more compliant
with the new loudness standards.
3. With Input Level and Pre Process set cor-
rectly, it’s time to adjust other parameters:
ALC Target on the Setup page determines
if the correction is optimized for hitting the
Target in 5.1 format, or for hitting it as a
stereo downmix. Because of the phase-ag-
nostic BS.1770 measurement (as opposed
to the summing of audio signals), you can’t
make every program hit the mark when lis-
tened to either way, so it’s up to you to pri-
oritize which should be closer.
4. Now decide how much dynamic correction
can be allowed by adjusting the Max Re-
duction and Max Boost parameters. For not
normalized programs, typically leave Max
Reduction at its maximum setting 20 dB,
i.e. allowing ALC6 to reduce loudness as
much as necessary. Max Boost, however,
should be limited so ALC6 doesn’t shift the
balance between foreground sound and
background sound too much. Don’t normal-
ly set Max Boost higher than 8 dB unless
there are good reasons for doing so.
5. Adjust Correction, which predominantly
works in tandem with Max Boost, to correct
soft foreground sounds just enough. 35%
is a good starting point, meaning that 1/3
of the deviation below Target level will be
corrected (provided Max Boost allows it).
For instance, if the input drops 10 dB below
Target, ALC6 will counteract 3.5 dB of that
drop.
6. Adjust Stridency Reduction to determine
how ALC6 deals with sounds louder than
Target. When set to “Off”, the same Correc-
tion amount is used below and above Tar-
get level. Fig 4 shows how different Striden-
cy Reduction settings affects loud sounds.
7. Adjust Freeze Level to define a point below
which a dynamic boost is revoked, so inten-
tional background sound isn’t brought up
too much. Note how this parameter relates
to Target level.
8. Set Target shift using the Pre Limit Gain
controls on the Limit page.
For HDTV, leave the controls at 0.0 dB.
For transmission to mobile platforms, enter
the Target shift required. For instance, if the
HDTV Target level is -23 LUFS/LKFS and
mobile platforms are aimed at -16 LUFS,
enter +7.0 dB as Pre Limit Gain on all three
controls.
9. Set the limiter parameters suitably. For
HDTV transmission, typically set the lim-
iter threshold between -3 and -6 dBTP. For
IPTV, mobile platforms and podcast, set the
threshold between 0 and -1 dBTP.
10. An LM6 meter may be attached to the input
of ALC6 in order to give relevant feedback
to production, and to trim ALC6 Input Level
over time.
11. An LM6 meter may also be attached to the
output of the processor to hit the desired
target as consistently as possible from day
to day. To achieve this, trim the three Pre
Limit Gain controls on the Limit page. If
you need more trim than ±1 dB, go through
stages 2 to 7 again.
12. Finally, consider to switch ALC6 presets
based on program. In case content is al-
ready normalized, only true-peak limiting
may be required. However, “rogue” content
could be assigned more pronounced pro-
cessing.