AK4642EN Datasheet, PDF (37/83 Pages) Asahi Kasei Microsystems – Stereo CODEC with MIC/HP/SPK-AMP

ASAHI KASEI
[AK4642EN]
2. ALC Recovery Operation
The ALC recovery operation waits for the WTM1-0 bits (Table 24) to be set after completing the ALC limiter operation.
If the input signal does not exceed “ALC recovery waiting counter reset level” (Table 21) during the wait time, the ALC
recovery operation is done. The IVL and IVR values are automatically incremented by RGAIN1-0 bits (Table 25) up to
the set reference level (Table 26) with zero crossing detection which timeout period is set by ZTM1-0 bits (Table 23).
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
WTM1-0 bits. When zero cross is detected at both channels during the wait period set by WTM1-0 bits, the ALC recovery
operation waits until WTM1-0 period and the next recovery operation is done.
For example, when the current IVOL value is 30H and RGAIN1-0 bits are set to “01”, IVOL 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 IVOL value exceeds
the reference level (REF7-0), the IVOL 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.
WTM1
0
0
1
1
WTM0
ALC Recovery Operation Waiting Period
8kHz
16kHz
44.1kHz
0
128/fs
16ms
8ms
2.9ms
1
256/fs
32ms
16ms
5.8ms
0
512/fs
64ms
32ms
11.6ms
1
1024/fs
128ms
64ms
23.2ms
Table 24. ALC Recovery Operation Waiting Period
Default
RGAIN1
0
0
1
1
RGAIN0
GAIN STEP
0
1 step
0.375dB
1
2 step
0.750dB
0
3 step
1.125dB
1
4 step
1.500dB
Table 25. ALC Recovery GAIN Step
Default
REF7-0
GAIN(dB)
Step
F1H
+36.0
F0H
+35.625
EFH
+35.25
:
:
E2H
+30.375
E1H
+30.0
0.375dB Default
E0H
+29.625
:
:
03H
−53.25
02H
−53.625
01H
−54.0
00H
MUTE
Table 26. Reference Level at ALC Recovery operation
MS0420-E-00
- 37 -
2005/09