
[AK4671] 
MS0666-E-00 
2007/10 
- 67 - 
■
 ALC Operation 
The ALC (Automatic Level Control) is executed by ALC block when ALC bit is “1”. ALC circuit operates at playback 
path for Playback mode and operates at recording path for Recording mode as shown in 
Figure 60
. 
1.
ALC Limiter Operation 
During the ALC limiter operation, when either Lch or Rch exceeds the ALC limiter detection level (
Table 24
), the IVL 
and IVR values (same value) are attenuated automatically by the amount defined by the ALC limiter ATT step (
Table 25
). 
When ZELMN bit = “0” (zero cross detection is enabled), the IVL and IVR values are changed by ALC limiter operation 
at the individual zero crossing points of Lch and Rch or at the zero crossing timeout. ZTM1-0 bits set the zero crossing 
timeout period of both ALC limiter and recovery operation (
Table 26
). IVL and IVR values are attenuated 1 step 
immediately (period: 1/fs) by ALC limiter operation when output level is over FS (Digital Full Scale). When output level 
is not over FS, the IVL and IVR values are changed at the individual zero crossing points of Lch and Rch or at the zero 
crossing timeout. 
When ZELMN bit = “1” (zero cross detection is disabled), IVL and IVR values are immediately (period: 1/fs) changed by 
ALC limiter operation. Attenuation step is fixed to 1 step regardless of the setting of LMAT1-0 bits. 
The attenuation operation is done continuously until the input signal level becomes ALC limiter detection level (
Table 24
) 
or less. After completing the attenuate operation, unless ALC bit is changed to “0”, the operation repeats when the input 
signal level exceeds LMTH1-0 bits. 
LMTH1 
LMTH0 
ALC Limier Detection Level
ALC Recovery Waiting Counter Reset Level 
0 
0 
ALC Output 
≥
2.5dBFS 
0 
1 
ALC Output 
≥
4.1dBFS 
1 
0 
ALC Output 
≥
6.0dBFS 
1 
1 
ALC Output 
≥
8.5dBFS 
Table 24. ALC Limiter Detection Level / Recovery Counter Reset Level 
ALC Limiter ATT Step 
LMAT1 
LMAT0 
ALC Output 
≥
 LMTH 
≥
 FS 
0 
0 
1 
1 
0 
1 
2 
2 
1 
0 
2 
4 
1 
1 
1 
2 
Table 25. ALC Limiter ATT Step  
Zero Crossing Timeout Period 
ZTM1 
ZTM0 
8kHz 
0 
0 
128/fs 
16ms 
0 
1 
256/fs 
32ms 
1 
0 
512/fs 
64ms 
1 
1 
1024/fs 
128ms 
Table 26. ALC Zero Crossing Timeout Period 
(default)
2.5dBFS > ALC Output 
≥
4.1dBFS 
4.1dBFS > ALC Output 
≥
6.0dBFS 
6.0dBFS > ALC Output 
≥
8.5dBFS 
8.5dBFS > ALC Output 
≥
12dBFS 
ALC Output 
ALC Output 
≥
 FS + 6dB 
1 
2 
4 
4 
 ALC Output 
≥
 FS + 12dB 
1 
2 
8 
8 
(default)
(default) 
16kHz 
8ms 
16ms 
32ms 
64ms 
44.1kHz 
2.9ms 
5.8ms 
11.6ms 
23.2ms