[AK4646]
2. ALC Recovery Operation
The ALC recovery operation waits for the WTM2-0 bits (Table 26) to be set after completing the ALC limiter operation.
If the input signal does not exceed “ALC recovery waiting counter reset level” (Table 23) during the wait time, the ALC
recovery operation is done. The VOL value is automatically incremented by RGAIN1-0 bits (Table 27) up to the set
reference level (Table 28) with zero crossing detection which timeout period is set by ZTM1-0 bits (Table 25). Then the
IVL and IVR are set to the same value for both channels. The ALC recovery operation is done at a period set by WTM2-0
bits. When zero cross is detected at both channels during the wait period set by WTM2-0 bits, the ALC recovery operation
waits until WTM2-0 period and the next recovery operation is done.
For example, when the current VOL value is 30H and RGAIN1-0 bits are set to “01”, VOL is changed to 32H by the auto
limiter operation and then the input signal level is gained by 0.75dB (=0.375dB x 2). When the VOL value exceeds the
reference level (REF7-0), the VOL values are not increased.
When
“ALC recovery waiting counter reset level (LMTH1-0) ≤ Output Signal < ALC limiter detection level (LMTH1-0)”
during the ALC recovery operation, the waiting timer of ALC recovery operation is reset. When
“ALC recovery waiting counter reset level (LMTH1-0) > Output Signal”,
the waiting timer of ALC recovery operation starts.
The ALC operation corresponds to the impulse noise. If an impulse noise is input when FR bit = “0”, the ALC recovery
operation becomes faster than a normal recovery operation. When large noise is input to 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 30). When FR bit = “1”, this fast recovery operation is not executed even if an
impulse noise is input.
ALC Recovery Operation Waiting Period
WTM2
WTM1
WTM0
8kHz
16kHz
44.1kHz
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
0
1
0
1
0
1
0
1
128/fs
256/fs
512/fs
1024/fs
2048/fs
4096/fs
8192/fs
16384/fs
16ms
32ms
64ms
128ms
256ms
512ms
1024ms
2048ms
8ms
16ms
32ms
64ms
128ms
256ms
512ms
1024ms
2.9ms
5.8ms
(default)
11.6ms
23.2ms
46.4ms
92.9ms
185.8ms
371.5ms
Table 26. ALC Recovery Operation Waiting Period
RGAIN1
RGAIN0
GAIN STEP
0
0
1
1
0
1
0
1
1 step
0.375dB
0.750dB
1.125dB
1.500dB
(default)
2 step
3 step
4 step
Table 27. ALC Recovery GAIN Step
MS0557-E-05
2011/01
- 39 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
