STA308 STMicroelectronics, STA308 Datasheet - Page 23

• Manufacturer Part Number: STA308
• Description: IC AUDIO PROCESSOR DGTL 64-TQFP
• Manufacturer: STMicroelectronics
• Series: DDX™r
• Type: Audio Processorr

Specifications of STA308

• Mounting Type: Surface Mount
• Package / Case: 64-TQFP, 64-VQFP
• Case: QFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Applications: -

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 STA308 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 register setting for that limiter. The
gain reduction occurs on a peak-detect algorithm.
The release of limiter (uncompression), when the gain is again increased, is dependent on a RMS-detect algo-
rithm. 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 threshold, the gain is again increased (uncompressed) at a rate dependent upon the Release Rate
register. The gain can never be increased past its 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 threshold 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.
Table 7. Channel Limiter Mapping as a function of CxLS bits.
Table 8. Limiter Attack Rate as a function of LxA bits.
note: Shaded areas are Default Settings
LxA(3..0)
LxA(3..0)
0001
0010
0011
0000
0110
0111
1000
1001
1010
1011
1100
1101
1110
1111
CxLS(1,0)
00
01
10
Channel is mapped to limiter #1
Channel is mapped to limiter #2
Channel has limiting disabled
Attack Rate dB/ms
Channel Limiter Mapping
1.3536
0.9024
0.4512
0.2256
0.1504
0.1123
0.0902
0.0752
0.0645
0.0564
0.0501
0.0451
STA308
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