AK4951AEN Datasheet, PDF (45/105 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/HP/SPK-AMP

[AK4951A]
(3) Stereo Separation Emphasis Filter (FIL3)
The FIL3 is used to emphasize the stereo separation of stereo microphone recording data and playback
data. F3A13-0 bits and F3B13-0 bits set the filter coefficients of the FIL3. When F3AS bit = “0”, the FIL3
performs as a High Pass Filter (HPF), and it performs as a Low Pass Filter (LPF) when F3AS bit = “1”.
FIL3 bit controls ON/OFF of the FIL3. When the stereo separation emphasis filter is OFF, the audio data
passes this block by 0dB gain. The coefficient should be set when FIL3 bit or PMPFIL bit is “0”. The FIL3
starts operation 4/fs(max) after when FIL3 bit = PMPFIL bit = “1” is set.
1) In case of setting FIL3 as HPF
fs: Sampling Frequency
fc: Cutoff Frequency
K: Gain [dB] (0dB  K  10dB)
Register Setting (Note 37)
FIL3: F3AS bit = “0”, F3A[13:0] bits =A, F3B[13:0] bits =B
(MSB=F3A13, F3B13; LSB=F3A0, F3B0)
1 / tan (fc/fs)
A = 10^K/20 x
,
1 + 1 / tan (fc/fs)
1  1 / tan (fc/fs)
B=
1 + 1 / tan (fc/fs)
Transfer Function
1  z ^1
H(z) = A
1 + Bz ^1
The cut-off frequency must be set as below.
fc/fs  0.0001 (fc min = 4.8Hz @fs=48kHz)
2) In case of setting FIL3 as LPF
fs: Sampling Frequency
fc: Cutoff Frequency
K: Gain [dB] (0dB  K  10dB)
Register Setting (Note 37)
FIL3: F3AS bit = “1”, F3A[13:0] bits =A, F3B[13:0] bits =B
(MSB=F3A13, F3B13; LSB= F3A0, F3B0)
1
A = 10^K/20 x
,
1 + 1 / tan (fc/fs)
1  1 / tan (fc/fs)
B=
1 + 1 / tan (fc/fs)
Transfer Function
1 + z ^1
H(z) = A
1 + Bz ^1
The cut-off frequency must be set as below.
fc/fs  0.0001 (fc min = 4.8Hz @fs=48kHz)
016001936-E-00
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2016/03