[AK4458]
014011794-E-01
2015/08
- 46 -
■
Out of Band Noise Reduction Filter
(PCM mode, DSD mode)
The AK4458 has an out of band noise reduction filter that can change frequency response. This FIR filter
attenuates out of band noise and prevents a degradation of the analog characteristics caused by a switching
regulator, etc. FIR2-0 bits set the frequency for noise attenuation. The filter characteristics will differ in DSD
direct mode compared with other modes (
Table 20
).
FIR2-0
bits
FIR
filter
Mode
FIR filter
Except DSD direct mode
DSD direct mode
000
0
1/4*[1 1 1 1 0 0 0 0 0 0 0 0 0 0 0 0]
1/2*[1 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0] (default)
001
1
1/4*[1 1 0 0 0 0 0 0 0 0 0 0 0 0 1 1]
1/2*[0 1 0 0 0 0 0 0 0 0 0 0 0 0 1 0]
010
2
1/4*[1 0 1 0 0 0 0 0 0 0 0 0 0 1 0 1]
1/2*[0 0 1 0 0 0 0 0 0 0 0 0 0 1 0 0]
011
3
1/4*[1 0 0 1 0 0 0 0 0 0 0 0 1 0 0 1]
1/2*[0 0 0 1 0 0 0 0 0 0 0 0 1 0 0 0]
100
4
1/4*[1 0 0 0 1 0 0 0 0 0 0 1 0 0 0 1]
1/2*[0 0 0 0 1 0 0 0 0 0 0 1 0 0 0 0]
101
5
1/4*[1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1]
1/2*[0 0 0 0 0 1 0 0 0 0 1 0 0 0 0 0]
110
6
1/4*[1 0 0 0 0 0 1 0 0 1 0 0 0 0 0 1]
1/2*[0 0 0 0 0 0 1 0 0 1 0 0 0 0 0 0]
111
7
1/4*[1 0 0 0 0 0 0 1 1 0 0 0 0 0 0 1]
1/2*[0 0 0 0 0 0 0 1 1 0 0 0 0 0 0 0]
Table 20. FIR Filter Setting
Figure 39. Mode0 FIR Filter (Except DSD direct mode)
Figure 40. Mode1 FIR Filter (Except DSD direct mode)
