Attack And Decay Times; Normal Mode - Cirrus Logic WM8940 Manual

Rev 4.4
Input
Signal
ALCSEL
PGA
Gain
V
step
Output
of PGA
Figure 13 ALC Limiter Mode Operation

ATTACK AND DECAY TIMES

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).

NORMAL MODE

ALCMODE = 0 (Normal Mode)
t
ALCATK
ATK
0000 104µs
0001 208µs
0010 416µs
0011 832µs
0100 1.66ms
0101 3.33ms
0110 6.66ms
0111 13.3ms
1000 26.6ms
1001 53.2ms
1010 106ms
t
DCYLIM
t
ATKLIM
Attack Time (s)
t t
ATK6dB ATK90%
832µs
1.66ms
3.33ms
6.66ms
13.3ms
26.6ms 192ms
53.2ms 384ms
106ms 767ms
213.2ms
426ms
852ms
WM8940
ALCLVL
6ms
12ms
24ms
48ms
96ms
1.53s
3.07s
6.13s
33