AK4649 Datasheet, PDF (45/96 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK-AMP

[AK4649]
ZTM1 bit
0
0
1
1
ZTM0 bit
0
1
0
1
Zero Crossing Timeout Period
8kHz
16kHz
44.1kHz
128/fs
16ms
8ms
2.9ms
256/fs
32ms
16ms
5.8ms
512/fs
64ms
32ms
11.6ms
1024/fs
128ms
64ms
23.2ms
Table 27. ALC Zero Crossing Timeout Period
(default)
2. ALC Recovery Operation
ALC recovery operation wait for the WTM2-0 bits (Table 28) to be set after completing ALC limiter operation. If the
input signal does not exceed “ALC recovery waiting counter reset level” (Table 25) during the wait time, ALC recovery
operation is executed. The VOL value is automatically incremented by RGAIN1-0 bits (Table 29) up to the set reference
level (Table 30) with zero crossing detection which timeout period is set by ZTM1-0 bits (Table 27). 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.
If the setting of 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 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 32)
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
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 28. ALC Recovery Operation Waiting Period
(default)
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 29. ALC Recovery GAIN Step
(default)
MS1023-E-01
- 45 -
2010/08