Solidyne 542 APC, Руководство пользователя

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the WB-AGC works with the main attack and recovery
times. If the input signal drops out of this window, the WB-
AGC reacts using the fast times defined in "Outside Win-
dow" (ATK / REL) until the input signal returns to the "Out-
side Window" range. Once the signal returns to those val-
ues, the WB-AGC continues to operate using the main at-
tack and recovery times until the signal reaches the Target
Level.
The "Outside Window" range is determined by the Fast
Window value, which is expressed in dB referring to the
Target Level. The level window will be:
From [Target Level – Fast Window] to [Target Level + Fast Window]
Example: Fast Window = 12dB; Target Level = -22dBfs;
then the Outside Winws will be -34dBfs to -10dBfs
The fast reaction times are determined by the ATK&REL
value and expressed in sec/6dB. Following the above ex-
ample, if ATK & REL is 1 sec/6dB and the input level drops
to -42dBfs, the WB-AGC will take 1 second to increase the
input level to the "Outside Window" range (-34dB). Once
that level is reached, the WB-AGC is still working but with
the main attack and recovery times.
TIPS

The attack and recovery times of the WB-AGC must be carefully
adjusted so that its action is not evident. If the attack time is
excessively long, the action of the WB-AGC may be noticeable
(level reduction may be noted). If the recovery time is very slow
and the attack time is very fast, when someone shouts (or a
cough or a laugh) the WB-AGC will reduce the level abruptly and
then it will take time to recover its gain. The effect will be simi-
lar to "someone turned down the volume of the radio".

For music, the recovery time should be long. If it is very short,
its action will become evident, and the volume contrasts (the
dynamics of music) will be completely lost.
4.5 Multiband AGC
While the Wide Band Automatic Gain Control (WB-AGC)
performs an adjustment of the overall level of the program
signal; the multi-band AGC (MB-AGC) performs a more
precise level control on each band, which allows:
•
Optimize the level in each frequency band. The
Multiband AGC can react faster than the WB-AGC
to contain or reinforce the signal in each band. De-
pending on how the bands are leveled, and the
spectral balance of the material, this increases the
loudness.
•
Print to the sound a consistent equalization profile
that will remain stable regardless of the character-
istics of the program signal.
•
Avoid excessive action of limiters when one or
more bands have high signal levels.
The multiband AGC stage (also known as "levelers") con-
trols the level in each frequency band, being able to attenu-
ate the level of a band to avoid that the compressor of that
band works in excess; or increase it to reach the compres-
sion threshold. For this, the MB-AGC defines a target level
for each band, and compensates the gains for the signal
to remain at the target level.
The MB-AGC indicators show the gain compensation of
each band, which is also shown in a timeline chart.
4.5.1 Dynamic EQ (Target levels)
Like the broadband AGC, each band is compensated ac-
cording to a target level . When the signal in a band is
greater than the target level, the AGC decreases the gain in
that band; while increasing it when the signal is below the
target level.
The maximum gain compensation applied is bounded by
the "ACTION RANGE" control. The value indicates in dB, in
each band, the maximum gain variation that will be applied
to approximate the signal at the target level. For example:
± 3dB limits the gain variation by 6dB, as the signal will be
attenuated or increased by up to 3 dB as appropriate.
If all target values are 0dB, the average spectral balance of
the music is maintained. If a target level is defined above
zero, that band will be emphasized since it will always tend
to have more energy than the others. Values below zero
attenuate the presence of that band. In this way, the target
levels of the MB-AGC allow to define an equalization pro-
file, based on the crossing frequencies of the filters
(125Hz, 800Hz, 2.5KHz and 8KHz).
Unlike a conventional equalizer, which emphasizes or at-
tenuates frequency ranges regardless of signal character-
istics; the MB-AGC behaves like a dynamic EQ because it
will reduce the gain of a band if its level is above the target
level, or amplify it when the level is lower. This technique
balances differences between different program materials
because if a material has strong bass, the MB-AGC attenu-
ates the bass band, but if the bass are weak, it strengthens
them, making the presence of bass is homogeneous over
time.
4.5.2 Band link
In order for the MB-AGC to not generate imbalances in the
spectral balance, which can occur due to excessive cor-
rection on one band in relation to the others, all the bands
are linked to the action of the MID-1 band . Each band has
a maximum deviation value (in dB) from the current MID-1
level. No band may have a level difference with respect to
MID-1 greater than the maximum allowable deviation.
When MID-1 changes its level, it can "drag" other bands
even though they are at the target level. For example, sup-
pose the allowed correction for the LOW band is 3dB and
for the rest it is 2dB. If MID-1 changes 4dB, it will drag 1dB
to the LOW band (it maintains 3dB difference) and 2dB to
the other bands (it maintains a difference of 2dB).
The user sets the maximum allowable correction for each
band in the "BAND LINK" section.
Page 34 Audio Processing Core - SOLIDYNE 542 APC