ak4671 AKM Semiconductor, Inc., ak4671 Datasheet - Page 68

• Manufacturer Part Number: ak4671
• Description: Stereo Codec With Mic/rcv/hp-amp
• Manufacturer: AKM Semiconductor, Inc.

2. ALC Recovery Operation
The ALC recovery operation waits for the WTM2-0 bits
If the input signal does not exceed “ALC recovery waiting counter reset level”
recovery operation is executed. The IVL and IVR values are automatically incremented by RGAIN1-0 bits
to the set reference level
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 is longer than
WTM2-0 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
during the ALC recovery operation, the waiting timer of ALC recovery operation is reset. When
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
MS0666-E-00
“ALC recovery waiting counter reset level (LMTH1-0) ≤ Output Signal < ALC limiter detection level (LMTH1-0)”
“ALC recovery waiting counter reset level (LMTH1-0) > Output Signal”,
WTM2
0
0
0
0
1
1
1
1
WTM1
0
0
1
1
0
0
1
1
(Table
RGAIN1
WTM0
0
0
1
1
29) with zero crossing detection which timeout period is set by ZTM1-0 bits
Table 27. ALC Recovery Operation Waiting Period
0
1
0
1
0
1
0
1
Table 28. ALC Recovery GAIN Step
RGAIN0
16384/fs
1024/fs
2048/fs
4096/fs
8192/fs
128/fs
256/fs
512/fs
0
1
0
1
(Table
(Table
- 68 -
1 step
2 step
3 step
4 step
ALC Recovery Operation Waiting Period
1024ms
2048ms
128ms
256ms
512ms
8kHz
16ms
32ms
64ms
GAIN STEP
30).
27) to be set after completing the ALC limiter operation.
0.375dB
0.750dB
1.125dB
1.500dB
1024ms
16kHz
128ms
256ms
512ms
16ms
32ms
64ms
8ms
(Table
(default)
24) during the wait time, the ALC
44.1kHz
185.8ms
371.5ms
11.6ms
23.2ms
46.4ms
92.9ms
2.9ms
5.8ms
(default)
(Table
(Table
[AK4671]
2007/10
28) up
26).