AK4637 Datasheet, PDF (52/96 Pages) Asahi Kasei Microsystems – 24bit Mono CODEC with MIC - SPK-AMP

[AK4637]
2. ALC Recovery Operation
ALC recovery operation wait for the WTM1-0 bits (Table 31) to be set after completing ALC limiter
operation. If the input signal does not exceed “ALC recovery waiting counter reset level” (Table 29) during
the wait time, ALC recovery operation is executed. The VOL value is automatically incremented by the
setting value of RGAIN2-0 bits (Table 32) up to the set reference level (Table 33) in every sampling.
When the VOL value exceeds the reference level (REF value), the VOL values are not increased. The
recovery speed gets slower when the VOL peak level exceeds -12dBFS to make the recovery speed for
low VOL level faster relatively.
When
“ALC recovery waiting counter reset level  Output Signal < ALC limiter detection level”
during the ALC recovery operation, the waiting timer of ALC recovery operation is reset. When
“ALC recovery waiting counter reset level > Output Signal”,
the waiting timer of ALC recovery operation starts.
ALC operations correspond to the impulse noise. When FRN bit = “0”, the impulse noise is input, the ALC
recovery operation becomes faster than a normal recovery operation. When large noise is input to a
microphone instantaneously, the quality of small level in the large noise can be improved by this fast
recovery operation. The speed of fast recovery operation is set by RFST1-0 bits (Table 34). When FRN
bit = “1”, the fast recovery does not operate though the impulse noise is input. Limiter amount of Fast
recovery is set by FRATT bit (Table 35).
WTM1
bit
0
0
1
1
WTM0
bit
ALC Recovery Cycle
8kHz
16kHz
48kHz
0
128/fs
16ms
8ms
2.7ms
1
256/fs
32ms
16ms
5.3ms
0
512/fs
64ms
32ms
10.7ms
1
1024/fs 128ms
64ms
21.3ms
Table 31. ALC Recovery Operation Waiting Period
(default)
RGAIN2 bit
0
0
0
0
1
1
1
1
RGAIN1 bit
RGAIN0 bit
GAIN Step [dB]
GAIN Change
Timing
0
0
0.00424
1/fs
0
1
0.00212
1/fs
1
0
0.00106
1/fs
1
1
0.00106
2/fs
0
0
0.00106
4/fs
0
1
0.00106
8/fs
1
0
0.00106
16/fs
1
1
0.00106
32/fs
Table 32. ALC Recovery Gain Step
(default)
015010680-E-00
- 52 -
2015/09