AK4950 Datasheet, PDF (43/106 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK/Cap-less VIDEO-AMP & mini DSP

[AK4950]
(3) Stereo Separation Emphasis Filter (FIL3)
FIL3 is used to emphasize the stereo separation of stereo microphone recording data and playback data. Address 0FH,
10H, 11H, 12H and 13H (3-wire mode, COEW bit = “1”), and address 8FH, 90H, 91H, 92H and 93H (I²C mode) set the
filter coefficients of FIL3. 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 PMPFIL bit = “0”. The FIL3 starts operation
2/fs(max) after when FIL3 bit =PMPFIL bit= “1” is set.
1) In case of setting FIL3 as LPF
fs: Sampling Frequency
fc: Cutoff Frequency
κ: Gain (0.25 ≤ κ ≤ 1) * κ_dB [dB], κ = 10^κdB/20
α = sin (2π fc / fs) / 2Q
Gain =20 log (Q)[dB] for fs. Normally Q should be set to 0.7071.
Register Setting (Register Map2) (Note 37)
1
A0: Register Addr = 0FH(3-wire mode), 8FH(I²C mode)
A1: Register Addr = 10H(3-wire mode), 90H(I²C mode)
A2: Register Addr = 11H(3-wire mode), 91H(I²C mode)
B1: Register Addr = 12H(3-wire mode), 92H(I²C mode)
B2: Register Addr = 13H(3-wire mode), 93H(I²C mode)
1– cos (2πfc/fs)
A0 = A2 =
×
2
1
1+ α
×κ
1– cos (2πfc/fs)
A1 =
1+ α
×κ
2 cos (2πfc/fs)
B1 =
1+ α
α –1
B2 = _{α +1}
Transfer Function
H_x (z) =
A₀ + A₁ z ^−1 + A₂z ^−2
1 − B₁z ^−1− B₂z ^−2
The cut-off frequency must be set as below.
fc / fs < 0.497
Setting Example) When fc=15kHz @ fs=44.1kHz. (I²C mode)
A0 = 03D96B (hex): Addr. 8FH
A1 = 07B2D5 (hex): Addr. 90H
A2 = 03D96B (hex): Addr. 91H
B1 = F53F37 (hex): Addr. 92H
B2 = FBF575 (hex): Addr. 93H
MS1320-E-00
- 43 -
2011/10