WM8985_07 WOLFSON [Wolfson Microelectronics plc], WM8985_07 Datasheet - Page 45

• Manufacturer Part Number: WM8985_07
• Description: Multimedia CODEC With Class D Headphone and Line Out
• Manufacturer: WOLFSON [Wolfson Microelectronics plc]

Pre-Production
LIMITER MODE
Figure 20 ALC Limiter Mode Operation
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ATTACK AND DECAY TIMES
In limiter mode, the ALC will reduce peaks that go above the threshold level, but will not increase the
PGA gain beyond the starting level. The starting level is the PGA gain setting when the ALC is
enabled in limiter mode. If the ALC is started in limiter mode, this is the gain setting of the PGA at
startup. If the ALC is switched into limiter mode after running in ALC mode, the starting gain will be
the gain at switchover. The diagram below shows an example of limiter mode.
The attack and decay times set the update times for the PGA gain. The attack time is the time
constant used when the gain is reducing. The decay time is the time constant used when the gain is
increasing. In limiter mode, the time constants are faster than in ALC mode. The time constants
are shown below in terms of a single gain step, a change of 6dB and a change of 90% of the PGAs
gain range.
Note that, these times will vary slightly depending on the sample rate used (specified by the SR
register).
PP, Rev 3.5, January 2007
WM8985
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