[AK4679]
2. ALC Recovery Operation
The ALC recovery operation waits for the WTM2-0 bits (Table 31) to be set after completing the ALC limiter operation.
If the input signal does not exceed “ALC recovery waiting counter reset level” (Table 28) during the wait time, the ALC
recovery operation is executed. The IVL and IVR values are automatically incremented by RGAIN1-0 bits (Table 32) up
to the set reference level (Table 33) with zero crossing detection which timeout period is set by ZTM1-0 bits (Table 30).
Then the IVL and IVR are set to the same value for both channels. The ALC recovery operation is executed in 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 executed. If ZTM1-0 bits is longer than
WTM2-0 bits and no zero crossing occurs, the ALC recovery operation is executed in a period set by ZTM1-0 bits.
For example, when the current IVL and IVR values are 30H and RGAIN1-0 bits are set to “01”, IVL and IVR values are
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 IVL and IVR values exceed the reference level (REF7-0 bits), the IVL and IVR 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 (Fast Recovery Operation). When large noise is input to microphone
instantaneously, the quality of small signal 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).
WTM2
bit
WTM1
bit
WTM0
bit
ALC Recovery Operation Waiting Period
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 31. ALC Recovery Operation Waiting Period
RGAIN1
RGAIN0
GAIN STEP
bit
bit
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 32. ALC Recovery GAIN Step
MS1402-E-06
2013/02
- 74 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
