ST STA380BW, Manual, Page: 33 / 162

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STA380BW Device overview
4.3.5 Attenuator
The attenuation is characterized by two different phases: attack and release.
Given an input signal above the limiter threshold, during the attack phase the STC
decreases the gain in order to reach the output level determined by the mapper. In this
process the key parameter is the attack rate (dB/ms) which determines how fast the STC
reacts according to the following equation:
where:

Output Signal Level is the attenuated signal coming from the attenuator block itself and
used as feedback

Mapper Level is the target signal level to be reached
The attack rate is user-selectable and its range is [0, +16] dB/ms with a 0.25 dB/ms step.
Given an input signal moving below the limiter threshold, during the release phase the STC
increases the gain in order to return the original input signal dynamic. In this process the key
parameter is the release rate (dB/ms) which determines how fast the STC releases the
attenuation on the input signal according to the following equation:
The release rate is user-selectable and its range is [0.0078, 1) dB/ms with a 0.0039 dB/ms
step.
4.3.6 Dynamic attack
Due to its dynamic, the input signal may exceed the limiter threshold by a variable amount of
decibels. In such different situations it might be useful to be able to tune the attack rate to
make the STC react slower or faster depending on the context. The attack rate value, set by
the user, can be dynamically varied through the dynamic attack rate (DAR). It is a parameter
(expressed in ms/dB) acting as a weighted coefficient, multiplying the difference between
the attenuator output signal and the mapper target level. The dynamic attack rate affects the
user-programmed attack rate according to the following equations:
The DAR is user-definable and its range of values is [0, +1) ms/dB, ( Table 11 ) with a
0.0039 ms/dB step. The DAR is the same for all 4 sub-bands.
AttackTime
OutputSignalLevel MapperLevel
–
AttackRate
-------------------------------------------------------------------------------------------------- =
ReleaseTime
OutputSignalLevel MapperLevel
–
ReleaseRate
-------------------------------------------------------------------------------------------------- =
DynamicAttackTime OutputSignalLevel MapperLevel
–
 
DAR

=
AttackTime
OutputSignalLevel MapperLevel
–
AttackRate
--------------------------------------------------------------------------------------------------
DynamicAttackTime
+ =
AttackRate

OutputSignalLevel MapperLevel
–
AttackTime DynamicAttackTime
–
-------------------------------------------------------------------------------------------------- =
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