[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 ≤ Kn ≤ 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)
2
tan (πfbn/fs)
1 − tan (πfbn/fs)
1 + tan (πfbn/fs)
An = Kn x
,
Cn =
Bn = cos(2π fon/fs) x
,
1 + tan (πfbn/fs)
1 + tan (πfbn/fs)
(n = 1, 2, 3)
Transfer function
H(z) = 1 + h1(z) + h2(z) + h3(z)
1 − z −2
hn (z) = An
1− Bnz −1− Cnz −2
(n = 1, 2, 3)
The center frequency should be set as below.
0.003 < fon / 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
2013/02
- 72 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
