Algorithm Manual Revision 4

ALC 6
174 System 6000 MKII Algorithms – Firmware version 6.5.0
ALC6 used for Ingest
1. Load a suitable ALC6 preset, then follow
these directions in the given order.
2. Use the LM6 radar meter in another engine
to measure unprocessed parts of the pro-
gram considered to be average foreground
level.
For a speech-based program, measure av-
erage speech.
For a music-based program, measure mez-
zo-forte parts/movements.
For a movie, anchors such as regular
speech or intro/outro music can be used.
When possible, avoid using Dolby’s speech
measurement algorithm (“Dialog Intelli-
gence”) as it doesn’t discriminate well be-
tween, for instance, speech and shouting.
For details, see the AES 135 paper “Level-
normalization of Feature Films using Loud-
ness vs Speech”. 1 to 2 minutes measuring
of representative parts of the program is
generally enough for a measurement.
3. Enter the difference between Target level
and the average loudness measurement
from above as Input Level on the Main page
of ALC6. For instance, if average parts of
the program have been measured at -27.5
LUFS/LKFS, and the Target is -24 LUFS/
LKFS, In Level should be set to +3.5 dB.
4. If a good ingest preset already exists, skip
items 5 to 11, but remember to go through
1 to 3 for each program to be ingested.
5. Set the Pre Process parameter on the ALC
page to “Normalized”.
6. 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.
7. Decide how much dynamic correction can
be allowed by adjusting the Max Reduction
and Max Boost parameters. Often leave
Max Reduction at its maximum setting 20
dB, i.e. allowing ALC6 to reduce loudness
as much as necessary. Max Boost, howev-
er, 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.
8. Adjust Correction, which predominantly
works in tandem with Max Boost, to bring
up soft foreground sound 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.
9. 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.
10. 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.
11. Set the limiter parameters suitably.
For HDTV delivery, typically set the limiter
threshold between -3 and -6 dBTP.
For IPTV, mobile platforms and podcast,
set the threshold between 0 and -1 dBTP.