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AK4671_10 Datasheet, PDF (63/166 Pages) Asahi Kasei Microsystems – Stereo CODEC with MIC/RCV/HP-AMP | |||
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[AK4671]
â Digital Programmable Filter
(1) High Pass Filter (HPF)
Normally, this HPF is used for a Wind-Noise Reduction Filter. This is composed of 2 steps of 1st order HPF. The
coefficient of both HPF is the same and set by F1A13-0 bits and F1B13-0 bits. HPFAD bit controls ON/OFF of the 1st
step HPF and HPF bit controls ON/OFF of the 2nd step HPF. When the HPF is OFF, the audio data passes this block by
0dB gain. The coefficient should be set when HPFAD=HPF bits = â0â or PMADL=PMADR=PMDAL=PMDAR bits =
â0â.
fs: Sampling frequency
fc: Cut-off frequency
Register setting (Note 61)
HPF: F1A[13:0] bits =A, F1B[13:0] bits =B
(MSB=F1A13, F1B13; LSB=F1A0, F1B0)
1 / tan (Ïfc/fs)
A=
,
1 + 1 / tan (Ïfc/fs)
1 â 1 / tan (Ïfc/fs)
B=
1 + 1 / tan (Ïfc/fs)
Transfer function
1 â z â1
H(z) = A
1 + Bz â1
The cut-off frequency should be set as below.
fc/fs ⥠0.0001 (fc min = 4.41Hz at 44.1kHz)
(2) Low Pass Filter (LPF)
This is composed with 1st order LPF. F2A13-0 bits and F2B13-0 bits set the coefficient of LPF. LPF bit controls ON/OFF
of the LPF. When the LPF is OFF, the audio data passes this block by 0dB gain. The coefficient should be set when LPF
bit = â0â or PMADL=PMADR=PMDAL=PMDAR bits = â0â.
fs: Sampling frequency
fc: Cut-off frequency
Register setting (Note 61)
LPF: F2A[13:0] bits =A, F2B[13:0] bits =B
(MSB=F2A13, F1B13; LSB=F2A0, F2B0)
1
A=
,
1 + 1 / tan (Ïfc/fs)
1 â 1 / tan (Ïfc/fs)
B=
1 + 1 / tan (Ïfc/fs)
Transfer function
1 + z â1
H(z) = A
1 + Bz â1
The cut-off frequency should be set as below.
fc/fs ⥠0.05 (fc min = 2205Hz at 44.1kHz)
MS0666-E-02
- 63 -
2010/06
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