ASAHI KASEI
[AK4644]
Digital EQ/HPF/LPF
The AK4644 performs wind-noise reduction filter, stereo separation emphasis, gain compensation and ALC (Automatic
Level Control) by digital domain for A/D converted data (Figure 35). FIL1, FIL3 and EQ blocks are IIR filters of 1st
order. The filter coefficient of FIL3, EQ and FIL1 blocks can be set to any value. Refer to the section of “ALC operation”
about ALC.
When only DAC is powered-up, digital EQ/HPF/LPF circuit operates at playback path. When only ADC is powered-up
or both ADC and DAC are powered-up, digital EQ/HPF/LPF circuit operates at recording path. Even if the path is
switched from recording to playback, the register setting of filter coefficient at recording remains. Therefore, FIL3, EQ,
FIL1 and GN1-0 bits should be set to “0” if digital EQ/HPF/LPF is not used for playback path.
PMADL bit, PMADR bit PMDAC bit LOOP bit
Status
Power-down
Playback
Digital EQ/HPF/LPF
Power-down
0
1
0
x
x
x
0
1
Default
“00”
Playback path
Recording
Recording & Playback
Recording Monitor Playback
Recording path
Recording path
Recording path
“01”, “10” or “11”
1
Note 37. Stereo separation emphasis circuit is effective only at stereo operation.
Table 25. Digital EQ/HPF/LPF Cirtcuit Setting (x: Don’t care)
FIL3 coefficient also sets the attenuation of the stereo separation emphasis.
The combination of GN1-0 bit (Table 26) and EQ coefficient set the compensation gain.
FIL1 and FIL3 blocks become HPF when F1AS and F3AS bits are “0” and become LPF when F1AS and F3AS bits are
“1”, respectively.
When EQ and FIL1 bits are “0”, EQ and FIL1 blocks become “through” (0dB). When FIL3 bit is “0”, FIL3 block become
“MUTE”. When each filter coefficient is changed, each filter should be set to “through” (“MUTE” in case of FIL3).
When MIX bit = “1”, only FIL1 is available. In this case, EQ and FIL3 bits should be set to “0”.
Wind-noise reduction
FIL1
Stereo separation emphasis
FIL3
Gain compensation
EQ
Gain
ALC
Any coefficient
F1A13-0
F1B13-0
F1AS
Any coefficient
Any coefficient
EQA15-0
EQB13-0
GN1-0
+24/+12/0dB
0dB -10dB
MUTE
(set by
FIL3 coefficient)
∼
F3A13-0
F3B13-0
F3AS
EQC15-0
+12dB 0dB
∼
Figure 35. Digital EQ/HPF/LPF
GN1
GN0
Gain
0dB
+12dB
+24dB
0
0
1
0
1
x
Default
Table 26. Gain select of gain block (x: Don’t care)
MS0477-E-01
2006/10
- 39 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
