AK4343 Datasheet, PDF (41/98 Pages) Asahi Kasei Microsystems – Stereo DAC with HP/RCV/SPK-AMP

ASAHI KASEI
[AK4343]
2. ALC Recovery Operation
The ALC recovery operation waits for the WTM2-0 bits (Table 27) to be set after completing the ALC limiter operation.
If the input signal does not exceed “ALC recovery waiting counter reset level” (Table 24) during the wait time, the ALC
recovery operation is done. The AVL and AVR values are automatically incremented by RGAIN1-0 bits (Table 28) up to
the set reference level (Table 29) with zero crossing detection which timeout period is set by ZTM1-0 bits (Table 26).
Then the AVL and AVR are set to the same value for both channels. The ALC recovery operation is done at 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 done. If ZTM1-0 is longer than
WTM2-0 and no zero crossing occurs, the ALC recovery operation is done at a period set by ZTM1-0 bits.
For example, when the current AVOL value is 30H and RGAIN1-0 bits are set to “01”, AVOL 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 AVOL value exceeds
the reference level (REF7-0), the AVOL 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 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 30).
WTM2
0
0
0
0
1
1
1
1
WTM1
0
0
1
1
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
0
2048/fs
256ms
128ms
46.4ms
1
4096/fs
512ms
256ms
92.9ms
0
8192/fs
1024ms
512ms
185.8ms
1
16384/fs
2048ms
1024ms
371.5ms
Table 27. 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 28. ALC Recovery GAIN Step
Default
MS0478-E-01
- 41 -
2006/10