[AK4753]
■ HPF and LPF Coefficients
HPF and LPF are controlled by 1FILSEL and 2FILSEL bits. When 1FILSEL and 2FILSEL bits= “1”, this block works
as a HPF. When 1FILSEL and 2FILSEL bits= “0”, this block works as a LPF. ON/OFF switching of this block can be
controlled by 1FILEN and 2FILEN bits. When the block of HPF/LPF becomes OFF mode by 1FILEN and 2FILEN
bits= “0”, the audio data passes this block by 0dB gain. The setting of the coefficients should be made when the
AK4753 is in the state that 1FILEN bit =2FILEN bit= “0”.
fs: Sampling frequency
fc: Cutoff frequency (-6dB point)
Register setting (Note 22)
1FA19-0, 2FA19-0 bits = A
1FB19-0, 2FB19-0 bits = B
1FC19-0, 2FC19-0 bits = C
1FILSEL bit
2FILSEL bit
“0” (LPF)
“1” (HPF)
πfc
1 tan2
⎛
⎜
⎝
⎞
⎟
⎠
1
fs
1
4
⎛
⎜
⎞
⎟
A
B
C
πfc
πfc
2
⎛
⎜
⎞
⎟
⎛
⎜
⎞
⎟
1
4
1+ 2 cos
π
tan
+1 tan
⎛
⎜
⎞
⎟
πfc
πfc
2
⎛
⎜
⎝
⎞
⎟
⎠
⎛
⎜
⎝
⎞
⎟
⎠
fs
fs
1+ 2 cos
π
tan
+1 tan
⎝
⎠
⎝
⎠
⎝
⎠
fs
fs
⎝
⎠
πfc
1−1 tan2
⎛
⎜
⎝
πfc
⎞
⎟
⎠
fs
2×
1
4
⎛
⎜
⎞
⎟
πfc
2
⎛
⎜
⎝
⎞
⎟
⎠
⎛
⎜
⎝
⎞
⎟
1+ 2 cos
π
tan
+1 tan
fs
fs
⎠
⎝
⎠
1
4
1
4
⎛
⎜
⎞
⎟
πfc
πfc
πfc
2
⎛
⎜
⎝
⎞
⎟
⎠
⎛
⎜
⎝
⎞
⎟
⎠
1− 2 cos
π
π
tan
tan
+1 tan
+1 tan
fs
fs
fs
fs
⎝
⎠
⎛
⎞
πfc
2
⎛
⎜
⎝
⎞
⎟
⎠
⎛
⎜
⎝
⎞
⎟
⎠
1+ 2 cos
⎜
⎟
⎝
⎠
2
2
1− 2z−1 + z−2
1+ Bz−1 + Cz−2
1+ 2z−1 + z−2
1+ Bz−1 + Cz−2
⎛
⎞
⎛
⎞
Transfer
function
⎜
⎟
⎟
⎜
⎟
⎟
H(z) = A
H(z) = A
⎜
⎜
⎝
⎠
⎝
⎠
The cutoff frequency should be set within the range as follows.
HPF:
LPF:
1.042x10-3≤fc/fs≤0.24
5.208x10-3≤fc/fs≤0.24
fc_min = 50Hz fc_max = 11.5kHz @ fs=48kHz
fc_min = 250Hz fc_max = 11.5kHz @ fs=48kHz
Other fs settings lower than above for LPF are shown in Table 29.
fc/fs
1.921x10-3
2.137x10-3
2.333x10-3
:
fc(@fs=48kHz)
A(dec)
B(dec)
-259845
-259624
-259426
:
C(dec)
128793
128576
128382
:
94.8Hz
103.9Hz
112.0Hz
:
5
6
7
:
:
:
:
34
:
:
5.208x10-3
250Hz
-256079
125144
Table 29. Low Frequency Band Setting of LPF
MS1311-E-00
2011/07
- 42 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
