AK4649 Datasheet, PDF (41/96 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK-AMP

[AK4649]
(3) Stereo Separation Emphasis Filter (FIL3)
FIL3 is used to emphasize the stereo separation of a stereo microphone recording data or playback data. F3A13-0 and
F3B13-0 bits set the filter coefficient of FIL3. FIL3 becomes High Pass Filter (HPF) at F3AS bit = “0”, and Low Pass
Filter (LPF) at F3AS bit = “1”. FIL3 bit controls ON/OFF of the FIL3. When Stereo Separation Emphasis Filter is OFF,
the audio data passes this block by 0dB gain. The coefficient, must be set when FIL3 bit = “0” or PMPFIL bit = “0”. The
FIL3 starts operation 4/fs(max) after when FIL3 bit= PMPFIL bit= “1” is set.
1) When FIL3 is set to “HPF”
fs: Sampling frequency
fc: Cut-off frequency
K: Filter gain [dB] (0dB ≥ K ≥ −10dB)
Register setting (Note 36)
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) When FIL3 is set to “LPF”
fs: Sampling frequency
fc: Cut-off frequency
K: Filter gain [dB] (0dB ≥ K ≥ −10dB)
Register setting (Note 36)
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
MS1023-E-01
- 41 -
2010/08