Algorithm Manual Revision 4

ALC 6
170 System 6000 MKII Algorithms – Firmware version 6.5.0
rides Corrections when the input level is higher
than Target.
Stridency Reduction
As consumers, once we have adjusted the gain
for a suitable sound pressure level, we are more
tolerant of loudness dropping than of loudness
going up – see “Loudness Descriptors to Char-
acterize Wide Loudness-Range Material” from
the 127th AES conference, 2009.
This parameter determines how programs are
dealt with (see Fig 4), and it is influenced by the
Pre Process parameter.
When set to anything but “Off”, Stridency Re-
duction overrides the general Correction setting
for loud content.
Freeze Level
Freeze Level sets the level below which a Gain
Boost is gradually revoked. Use Freeze to avoid
boosting signals meant to remain below the
noise floor of a certain broadcast platform.
Freeze relates to Target Level. For instance, if
Target Level is set at –21 LFS, and Freeze Level
is set at –15dB, positive gain (if enabled) will be
gradually nulled as input level falls below –36
LKFS/LUFS.
Freeze Hold
Freeze Hold sets the time in seconds before the
processor resets to 0dB gain change once the
level falls below Freeze Level.
Average Rate
Average Rate sets the speed by which gain
changes as a result of loudness variations.
The rate adapts to the signal, and it takes the
Slow Window and Pre Process parameter set-
tings into account, so this parameter indicates
an average number.
A fast Average Rate is generally more asymmet-
rical than a slow rate: ALC6 becomes faster at
turning down than turning up because listeners
typically object more to obtrusively loud sounds
(promos, commercials) than to audio becoming
soft.
Slow Window
Slow Window sets a window around the Target
Level inside which gain changes happen more
slowly. Use this parameter in combination with
Average Rate. (6dB = ±3dB from target)
Pre Process
The parameter indicates the condition of the in-
put program – i.e., if it has already been normal-
ized to Target level or not. As procedures in pro-
duction and on the servers moves towards pro-
grams already having been normalized prior to
transmission, the amount of processing should
gradually be backed off.
Avoid quality-hampering “sausage processing”
by setting this parameter to indicate the correct
state of the input signal. The Pre Process param-
eter is included with Presets so it may conse-
quently be altered based on GPI, SNMP or serial
commands to the DB4 or DB8 frame.
When running ALC6 in a DB6 frame, SDI meta-
data (SMPE 2020) may also be used for this ap-
plication.