AK4649 Datasheet, PDF (42/96 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK-AMP

[AK4649]
(4) Gain Compensation
Gain Compensation is used to compensate the frequency response and the gain that is changed by Stereo Separation
Emphasis Filter. Gain Compensation is composed of the Equalizer (EQ0) and the Gain (0dB/+12dB/+24dB).
E0A15-0, E0B13-0 and E0C15-0 bits set the coefficient of EQ0. GN1-0 bits set the gain (Table 24). 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
must be set when EQ0 bit = “0” or PMPFIL bit = “0”. EQ0 starts operation 4/fs(max) after when EQ0=PMPFIL bits =
“1” is set.
fs: Sampling frequency
fc₁: Pole frequency
fc₂: Zero-point frequency
K: Filter gain [dB] (Maximum +12dB)
Register setting (Note 36)
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 35. EQ0 Frequency Response
GN1 bit
GN0 bit
Gain
0
0
0dB
(default)
0
1
+12dB
1
x
+24dB
Table 24. Gain select of gain block (x: Don’t care)
MS1023-E-01
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2010/08