Wolfson WM8978, Manual, Page: 40 / 119

WM8978
Production Data
w
PD, Rev 4.5, October 2011
40
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)
ALCATK
t
ATK
t
ATK6dB
t
ATK90%
0000 104µs 832µs 6ms
0001 208µs 1.66ms 12ms
0010 416µs 3.33ms 24ms
0011 832µs 6.66ms 48ms
0100 1.66ms 13.3ms 96ms
0101 3.33ms 26.6ms 192ms
0110 6.66ms 53.2ms 384ms
0111 13.3ms 106ms 767ms
1000 26.6ms 213.2ms 1.53s
1001 53.2ms 426ms 3.07s
1010 106ms 852ms 6.13s
Attack Time (s)
ALCMODE = 0 (Normal Mode)
ALCDCY
t
DCY
t
DCY6dB
t
DCY90%
0000 410µs 3.28ms 23.6ms
0001 820µs 6.56ms 47.2ms
0010 1.64ms 13.1ms 94.5ms
0011 3.28ms 26.2ms 189ms
0100 6.56ms 52.5ms 378ms
0101 13.1ms 105ms 756ms
0110 26.2ms 210ms 1.51s
0111 52.5ms 420ms 3.02s
1000 105ms 840ms 6.05s
1001 210ms 1.68s 12.1s
1010 420ms 3.36s 24.2s
Decay Time (s)
Table 18 ALC Normal Mode (Attack and Decay times)