AK4955 Datasheet, PDF (44/117 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK/Cap-less VIDEO-AMP/ LDO & DSP

[AK4955]
(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 42)
FIL3: F3AS bit = “0”, F3A[13:0] bits =A, F3B[13:0] bits =B
(MSB=F3A13, F3B13; LSB=F3A0, F3B0)
1 / tan (πfc/fs)
A = 10^K/20 x
,
1 + 1 / tan (πfc/fs)
1 − 1 / tan (πfc/fs)
B=
1 + 1 / tan (πfc/fs)
Transfer Function
1 − z ^−1
H(z) = A
1 + Bz ^−1
2) In case of setting FIL3 as LPF
fs: Sampling Frequency
fc: Cutoff Frequency
K: Gain [dB] (0dB ≥ K ≥ −10dB)
Register Setting (Note 42)
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 (πfc/fs)
1 − 1 / tan (πfc/fs)
B=
1 + 1 / tan (πfc/fs)
Transfer Function
1 + z ^−1
H(z) = A
1 + Bz ^−1
MS1343-E-00
- 44 -
2011/12