STA320 STMicroelectronics, STA320 Datasheet - Page 23

• Manufacturer Part Number: STA320
• Manufacturer: STMicroelectronics

Specifications of STA320

• Operating Temperature (min): -20C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Commercial
• Mounting: Surface Mount
• Lead Free Status / RoHS Status: Compliant

5.11.2Limiter 1 Attack/Release Threshold
5.11.3Limiter 2 Attack/Release Rate
5.11.4Limiter 2 Attack/Release Threshold
The STA320 includes 2 independent limiter blocks. The purpose of the limiters is to automatically reduce
the dynamic range of a recording to prevent the outputs from clipping in anti-clipping mode or to actively
reduce the dynamic range for a better listening environment such as a night-time listening mode which is
often needed for DVDs. The two modes are selected via the DRC bit in Configuration Register F, bit 0
address 0x05. Each channel can be mapped to either limiter or not mapped, meaning that channel will clip
when 0dBFS is exceeded. Each limiter will look at the present value of each channel that is mapped to it,
select the maximum absolute value of all these channels, perform the limiting algorithm on that value, and
then if needed adjust the gain of the mapped channels in unison.
The limiter attack thresholds are determined by the LxAT registers. It is recommended in anti-clipping
mode to set this to 0dBFS, which corresponds to the maximum unclipped output power of a DDX amplifier.
Since gain can be added digitally within the STA320 it is possible to exceed 0dBFS or any other LxAT
setting, when this occurs, the limiter, when active, will automatically start reducing the gain. The rate at
which the gain is reduced when the attack threshold is exceeded is dependent upon the attack rate reg-
ister setting for that limiter. The gain reduction occurs on a peak-detect algorithm. The release of limiter,
when the gain is again increased, is dependent on a RMS-detect algorithm. The output of the volume/
limiter block is passed through a RMS filter. The output of this filter is compared to the release threshold,
determined by the Release Threshold register. When the RMS filter output falls below the release thresh-
old, the gain is again increased at a rate dependent upon the Release Rate register. The gain can never
be increased past it's set value and therefore the release will only occur if the limiter has already reduced
the gain. The release threshold value can be used to set what is effectively a minimum dynamic range,
this is helpful as over-limiting can reduce the dynamic range to virtually zero and cause program material
to sound "lifeless".
In AC mode the attack and release thresholds are set relative to full-scale. In DRC mode the attack thresh-
old is set relative to the maximum volume setting of the channels mapped to that limiter and the release
threshold is set relative to the maximum volume setting plus the attack threshold.
Figure 5. Basic Limiter and Volume Flow Diagram.
L1AT3
L2AT3
L2A3
D7
D7
D7
0
0
0
L1AT2
L2AT2
L2A2
D6
D6
D6
1
1
1
Gain/Volume
Input
L1AT1
L2AT1
L2A1
D5
D5
D5
1
1
1
Gain
L1AT0
L2AT0
L2A0
D4
D4
D4
0
0
0
Attenuation
Limiter
L1RT3
L2RT3
L2R3
D3
D3
D3
1
1
1
Saturation
RMS
L1RT2
L2RT2
L2R2
D2
D2
D2
0
0
0
Output
L1RT1
L2RT1
L2R1
D1
D1
D1
0
1
0
L1RT0
L2RT0
STA320
L2R0
D0
D0
D0
1
0
1
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