AK4753 Datasheet, PDF (42/85 Pages) Asahi Kasei Microsystems – 2-in, 4-out CODEC with DSP Functions

[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
A
B
C
Transfer
function
“0” (LPF)
“1” (HPF)
1
1+ 2 cos⎜⎛ ¹ π ⎟⎞
⎝⁴ ⎠
tan⎜⎝⎛^πfc _fs ⎟⎠⎞ +1 tan²âŽœâŽâŽ›^πfc _fs ⎟⎠⎞
1 tan²âŽœâŽâŽ›^πfc _fs ⎟⎠⎞
1+ 2 cos⎜⎛ ¹ π ⎟⎞
⎝⁴ ⎠
tan⎜⎝⎛^πfc _fs ⎟⎠⎞ +1 tan²âŽœâŽâŽ›^πfc _fs⎟⎠⎞
2×
1−1 tan²âŽœâŽâŽ›^πfc _fs⎟⎠⎞
1+ 2 cos⎜⎛ ¹ π ⎟⎞
⎝⁴ ⎠
tan⎜⎝⎛^πfc _fs⎟⎠⎞ +1 tan²âŽœâŽâŽ›^πfc _fs⎟⎠⎞
1− 2 cos⎜⎛ ¹ π ⎟⎞
⎝⁴ ⎠
1+ 2 cos⎜⎛ ¹ π ⎟⎞
⎝⁴ ⎠
tan⎜⎝⎛^πfc _fs ⎟⎠⎞ +1 tan²âŽœâŽâŽ›^πfc _fs ⎟⎠⎞
tan⎜⎝⎛^πfc _fs ⎟⎠⎞ +1 tan²âŽœâŽâŽ›^πfc _fs⎟⎠⎞
H
(
z)
=
⎜⎜⎝⎛
1+ 2z^−1 + z^−2
A
1
+
Bz^−1
+
Cz^−2
⎟⎟⎠⎞²
H
(
z)
=
⎜⎜⎝⎛
1 − 2z^−1 + z^−2
A
1
+
Bz ^−1
+
Cz ^−2
⎟⎟⎠⎞²
The cutoff frequency should be set within the range as follows.
HPF: 1.042x10^-3≤fc/fs≤0.24
LPF: 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
:
:
5.208x10^-3
fc(@fs=48kHz) A(dec) B(dec) C(dec)
94.8Hz
5
-259845 128793
103.9Hz
6
-259624 128576
112.0Hz
7
-259426 128382
:
:
:
:
:
:
:
:
250Hz
34
-256079 125144
Table 29. Low Frequency Band Setting of LPF
MS1311-E-00
- 42 -
2011/07