AK4679EG Datasheet, PDF (72/220 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with DSP and MIC/RCV/HP/SPK/LINE-AMP

[AK4679]
(5) 3-band Equalizer
This block can be used as Equalizer or Notch Filter. 3-band Equalizer (EQ1, EQ2 and EQ3) is selected ON/OFF
independently by EQ1, EQ2 and EQ3 bits. When Equalizer is OFF, the audio data passes this block by 0dB gain.
E1A15-0, E1B15-0 and E1C15-0 bits set the coefficient of EQ1. E2A15-0, E2B15-0 and E2C15-0 bits set the coefficient
of EQ2. E3A15-0, E3B15-0 and E3C15-0 bits set the coefficient of EQ3. The EQx (x=1∼3) coefficient must be set when
EQx bit = “0” or PMPFIL bit = “0”. EQ1-3 start operation 4/fs(max) after when (EQx (x=1~3) = “1”) and PMPFIL bit =
“1” is set
fs: Sampling frequency
fo₁ ~ fo₃: Center frequency
fb₁ ~ fb₃: Band width where the gain is 3dB different from center frequency
K₁ ~ K₃ : Gain (−1 ≤ K_n ≤ 3)
Register setting (Note 77)
EQ1: E1A[15:0] bits =A₁, E1B[15:0] bits =B₁, E1C[15:0] bits =C₁
EQ2: E2A[15:0] bits =A₂, E2B[15:0] bits =B₂, E2C[15:0] bits =C₂
EQ3: E3A[15:0] bits =A₃, E3B[15:0] bits =B₃, E3C[15:0] bits =C₃
(MSB=E1A15, E1B15, E1C15, E2A15, E2B15, E2C15, E3A15, E3B15, E3C15; LSB= E1A0, E1B0, E1C0,
E2A0, E2B0, E2C0, E3A0, E3B0, E3C0)
A_n = K_n x
tan (πfb_n/fs)
1 + tan (πfb_n/fs)
(n = 1, 2, 3)
2
, B_n = cos(2π fo_n/fs) x
, ^{Cn =}
1 + tan (πfb_n/fs)
1 − tan (πfb_n/fs)
1 + tan (πfb_n/fs)
Transfer function
H(z) = 1 + h₁(z) + h₂(z) + h₃(z)
h_n (z) = A_n
1 − z ^−2
1− B_nz ^−1− C_nz ^−2
(n = 1, 2, 3)
The center frequency should be set as below.
0.003 < fo_n / fs < 0.497
Note 77. [Translation the filter coefficient calculated by the equations above from real number to binary code (2’s
complement)]
X = (Real number of filter coefficient calculated by the equations above) x 2¹³
X should be rounded to integer, and then should be translated to binary code (2’s complement).
MSB of each filter coefficient setting register is sine bit.
MS1402-E-06
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2013/02