STA382BWSTR datasheet(34/172 Pages) STMICROELECTRONICS

34 / 172 page

Device overview

STA382BWS

34/172

Doc ID 022784 Rev 1

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 12) 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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