Algorithm Manual Revision 4

ALC 6
English Manual – Updated 2018-02-28 175
ALC6 used for Live Production
Because of its low latency (0.8 ms, equivalent to
the time it takes sound to travel 25 cm or 10 inch-
es) and high resolution, ALC6 is also suitable for
providing a loudness and true-peak level safety
belt when live mixing, e.g. in OB trucks: You can
monitor after the processor without worrying
about mix-timing.
1. Load a suitable ALC6 preset, then follow
these directions in the given order.
2. Use a radar meter, LM6, in another engine
to measure the input of ALC6. Adjust mix
levels so that average foreground level is
close to the Target level, typically -23 or -24
LUFS/LKFS.
3. If a mix preset already exists, skip items 4
to 10, but remember to take note of 11 to 12.
4. Set the Pre Process parameter on the ALC
page to “Normalized”.
5. 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.
6. Decide how much ALC6 should be allowed
to influence the mix by adjusting the Max
Reduction and Max Boost parameters. Typ-
ically leave Max Reduction at its maximum
setting 20 dB, i.e. allowing ALC6 to reduce
loudness as much as necessary. If ALC6
brings down loud parts of a mix too much,
back-off Stridency Reduction rather than
lowering Max Reduction. Max Boost should
be limited so ALC6 doesn’t shift the bal-
ance between foreground sound and back-
ground sound too much. Don’t normally set
Max Boost higher than a few dB, if allowing
any at all, when doing a live mix.
7. 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 be-
low Target, ALC6 will counteract 3.5 dB of
that drop.
8. 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.
9. 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.
10. Set the limiter parameters suitably.
For HDTV delivery, typically set the limiter
threshold between -3 and -6 dBTP.
For universal delivery to several platforms,
one (less than ideal) option is to mix for low-
est common denominator, i.e. anticipating
a headroom of only 16 dB on mobile plat-
forms. In this case, set the limiter threshold
16 dB higher than your Target. If the Target
is, for example -24 LUFS, limiters are thus
set at -8 dBTP.
11. When performing a live mix, it’s a good idea
to have an LM6 meter at the input and one
at the output of ALC6 to check if the mix
needs adjustment, or if the processor does.
The two primary measurements to keep an
eye on are Sliding Loudness and Program
Loudness. The former should be set to 10-
30 seconds to give an idea if recent loud-
ness is above or below the program total,
while the latter should be reset only when
the program starts.
12. Generally start a live mix conservatively lev-
el-wise. Aim for example 1 LU below Target
level at the beginning. It’s easier to move
up during a program than moving down. To
gradually bring up the level, mix hotter and/
or reduce Stridency Reduction on the ALC
page and/or trim the Pre Limit Gain controls
on the Limit page.