AK4671_10 Datasheet, PDF (67/166 Pages) Asahi Kasei Microsystems – Stereo CODEC with MIC/RCV/HP-AMP

[AK4671]
■ 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
0
0
1
1
LMTH0 ALC Limier Detection Level ALC Recovery Waiting Counter Reset Level
0
ALC Output ≥ −2.5dBFS
−2.5dBFS > ALC Output ≥ −4.1dBFS
1
ALC Output ≥ −4.1dBFS
−4.1dBFS > ALC Output ≥ −6.0dBFS
0
ALC Output ≥ −6.0dBFS
−6.0dBFS > ALC Output ≥ −8.5dBFS
1
ALC Output ≥ −8.5dBFS
−8.5dBFS > ALC Output ≥ −12dBFS
Table 24. ALC Limiter Detection Level / Recovery Counter Reset Level
(default)
LMAT1
0
0
1
1
LMAT0
0
1
0
1
ALC Limiter ATT Step
ALC Output ALC Output ALC Output
≥ LMTH
≥ FS
≥ FS + 6dB
1
1
1
2
2
2
2
4
4
1
2
4
Table 25. ALC Limiter ATT Step
ALC Output
≥ FS + 12dB
1
2
8
8
(default)
ZTM1
0
0
1
1
ZTM0
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 26. ALC Zero Crossing Timeout Period
(default)
MS0666-E-02
- 67 -
2010/06