[AK4634]
2. ALC Recovery Operation
The ALC recovery operation waits for the WTM2-0 bits (Table 28) to be set after completing the ALC limiter operation.
If the input signal does not exceed “ALC recovery waiting counter reset level” (Table 25) during the wait time, the ALC
recovery operation is executed. The VOL value is automatically incremented by RGAIN1-0 bits (Table 29) up to the set
reference level (Table 30, Table 31) with zero crossing detection which timeout period is set by ZTM1-0 bits (Table 27).
The ALC recovery operation is executed in a period set by WTM2-0 bits.
For example, when the current VOL value is 30H and RGAIN1-0 bits are set to “01”(2 steps), 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 (IREF7-0 or OREF5-0), 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. When the impulse noise is input, 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 first recovery operation is set
by RFST1-0 bits (Table 32).
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 28. ALC Recovery Operation Waiting Period
RGAIN1
RGAIN0
GAIN STEP
0.375dB
0
0
1
1
0
1
0
1
1
2
3
4
(default)
0.750dB
1.125dB
1.500dB
Table 29. ALC Recovery GAIN Step
Rev. 0.5
2007/10
- 44 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
