AK4955 Datasheet, PDF (45/117 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK/Cap-less VIDEO-AMP/ LDO & DSP

[AK4955]
(4) Gain Compensation (EQ0)
Gain compensation is used to compensate the frequency response and the gain that is changed by the stereo separation
emphasis filter. Gain compensation is composed of the Equalizer (EQ0) and the Gain (0dB/+12dB/+24dB). E0A15-0 bits,
E0B13-0 bits and E0C15-0 bits set the coefficient of EQ0. GN1-0 bits set the gain (Table 26). EQ0 bit controls ON/OFF
of EQ0. When EQ is OFF and the gain is 0dB, the audio data passes this block by 0dB gain. The coefficient should be set
when EQ0 bit = “0” or PMPFIL bit = “0”. The EQ0 starts operation 4/fs(max) after when EQ0 bit =PMPFIL bit= “1” is
set.
fs: Sampling Frequency
fc₁: Polar Frequency
fc₂: Zero-point Frequency
K: Gain [dB] (Maximum setting is +12dB.)
Register Setting (Note 42)
E0A[15:0] bits =A, E0B[13:0] bits =B, E0C[15:0] bits =C
(MSB=E0A15, E0B13, E0C15; LSB=E0A0, E0B0, E0C0)
1 + 1 / tan (πfc₂/fs)
A = 10^K/20 x
,
1 + 1 / tan (πfc₁/fs)
1 − 1 / tan (πfc₁/fs)
B=
,
1 + 1 / tan (πfc₁/fs)
1 − 1 / tan (πfc₂/fs)
C =10^K/20 x
1 + 1 / tan (πfc₁/fs)
Transfer Function
H(z) =
A + Cz ^−1
1 + Bz ^−1
Gain[dB]
K
fc₁
fc₂
Frequency
Figure 42. EQ0 Frequency Response
GN1 bit
GN0 bit
Gain
0
0
0dB
(default)
0
1
+12dB
1
x
+24dB
Table 26. Gain Setting (x: Don’t care)
MS1343-E-00
- 45 -
2011/12