參數(shù)資料
型號： AK4642EN
廠商： Asahi Kasei Microsystems Co.,Ltd
元件分類： Codec
英文描述： Stereo CODEC with MIC/HP/SPK-AMP
中文描述： 立體聲編解碼器麥克風(fēng)/惠普/胰腎聯(lián)合移植腺苷
文件頁數(shù)： 37/83頁
文件大小： 670K
代理商： AK4642EN
ASAHI KASEI
[AK4642EN]
MS0420-E-00
2005/09
- 37 -
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.
ALC Recovery Operation Waiting Period
WTM1
WTM0
8kHz
0
0
128/fs
16ms
0
1
256/fs
32ms
1
0
512/fs
64ms
1
1
1024/fs
128ms
Table 24. ALC Recovery Operation Waiting Period
RGAIN1
RGAIN0
0
0
1 step
0
1
2 step
1
0
3 step
1
1
4 step
Table 25. ALC Recovery GAIN Step
REF7-0
GAIN(dB)
F1H
+36.0
F0H
+35.625
EFH
+35.25
:
:
E2H
+30.375
E1H
+30.0
E0H
+29.625
:
:
03H
53.25
02H
53.625
01H
54.0
00H
MUTE
Table 26. Reference Level at ALC Recovery operation
Default
16kHz
8ms
16ms
32ms
64ms
44.1kHz
2.9ms
5.8ms
11.6ms
23.2ms
GAIN STEP
Default
0.375dB
0.750dB
1.125dB
1.500dB
Step
Default
0.375dB
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