AK4955 Datasheet, PDF (48/117 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK/Cap-less VIDEO-AMP/ LDO & DSP

[AK4955]
2. ALC Recovery Operation
ALC recovery operation wait for the WTM2-0 bits (Table 30) to be set after completing ALC limiter operation. If the
input signal does not exceed “ALC recovery waiting counter reset level” (Table 27) during the wait time, ALC recovery
operation is executed. The VOL value is automatically incremented by RGAIN1-0 bits (Table 31) up to the set reference
level (Table 32) with zero crossing detection which timeout period is set by ZTM1-0 bits (Table 29). The ALC recovery
operation is executed in a period set by WTM2-0 bits. If the setting of ZTM1-0 bits is longer than WTM2-0 bits and no
zero crossing occurs, the ALC recovery operation is executed at a period set by ZTM1-0 bits.
For example, when the current VOL value is 30H and RGAIN1-0 bits are set to “01”, VOL is changed to 32H by auto
limiter operation and then the input signal level is gained by 0.75dB (=0.375dB x 2). When the VOL value exceeds the
reference level (REF7-0), the VOL 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.
ALC operations correspond 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 a microphone instantaneously, the quality of small
level in the large noise can be improved by this fast recovery operation. The speed of first recovery operation is set by
RFST1-0 bits (Table 34). The fast recovery operation is not executed when FRN bit = “1” even if an impulse noise is
input.
WTM2
bit
0
0
0
0
1
1
1
1
WTM1
bit
0
0
1
1
0
0
1
1
WTM0
bit
ALC Recovery Operation Waiting Period
8kHz
16kHz
48kHz
0
128/fs
16ms
8ms
2.7ms
1
256/fs
32ms
16ms
5.3ms
0
512/fs
64ms
32ms
10.7ms
1
1024/fs
128ms
64ms
21.3ms
0
2048/fs
256ms
1
4096/fs
512ms
128ms
256ms
42.7ms
85.3ms
0
8192/fs
1024ms
512ms
170.7ms
1
16384/fs
2048ms
1024ms
341.3ms
Table 30. ALC Recovery Operation Waiting Period
RGAIN1 bit
0
0
1
1
RGAIN0 bit
GAIN STEP
0
1 step
0.375dB
1
2 step
0.750dB
0
3 step
1.125dB
1
4 step
1.500dB
Table 31. ALC Recovery Gain Step
(default)
(default)
MS1343-E-00
- 48 -
2011/12