Algorithm Manual Revision 4
Table Of Contents
ALC 6
English Manual – Updated 2018-02-28 169
ALC6 – ALC page
Fig 3: ALC6 algorithm – ALC page
Target Level
Target Level sets the Loudness Target aimed
for by ALC6. The unit is shown as “LFS”, which
denotes “LKFS” as well as “LUFS” (the two are
identical).
For normal broadcast, the value should typically
be between -18 and -24 LFS. Note that the dis-
tance between this value and Limit Threshold on
the Limit page is a quality-defining factor – i.e.
the standard headroom of the station. To ensure
decent audio quality, headroom should be 16dB
or higher.
In broadcast environments working with a fixed
Dialnorm value, Target Level can be set 1 to 3dB
higher than the static Dialnorm value in order to
prevent level jumps between channels, and to
have the Dolby DRC system sound better, if in-
voked.
Stereo Offset
While the BS.1770 measurement works for ste-
reo as well as for 5.1 signals, a different Target
Level may be better in some distribution scenari-
os: When end-listener downmix is relied on, hav-
ing the same Target Level for stereo and for 5.1
can create systematic level jumps at consumers
listening to stereo. Therefore, ALC6 includes a
novel automatic discrimination function, allowing
for slightly different Target Levels to aim at if the
input format is stereo or if it is 5.1.
The Stereo Offset parameter allows a smooth
and automatic Target Level change when the
input is stereo. For instance, if Target Level is
set to -21 LFS and Stereo offset is set to -3 LU,
ALC6 uses a Target Level of -21 LFS for 5.1 pro-
grams, but a Target Level of -24 LFS for stereo.
Fig 4: ALC6 I/O level diagram
and parameter names
Max Reduction
Sets the maximum number of dBs the processor
is allowed to attenuate the signal.
If this parameter is set to 0.0dB, level reduction
is disabled regardless of other settings such as
Correction – see Fig 4.
Max Boost
Max Boost sets the maximum number of dBs the
processor is allowed to boost the signal. If this
parameter is set to 0.0dB, level boost is disabled
regardless of other settings such as Correction,
see Fig 4.
Correction
Sets how much correction is applied when the
actual loudness is different from the Target Level
– see Fig 4. For instance, if Correction is set at
40%, and loudness is 6dB away from the Tar-
get Level, the processor will apply a correction
of 2.4dB.
Be careful when setting this parameter, as it may
take a little “time testing” to arrive at the best val-
ue, especially if you wish to cover within program
level jumps and inter-program level jumps using
one preset. Note how Stridency Reduction over-