[AK4675]
(5) 5-band Notch
This block can be used as Equalizer or Notch Filter. 5-band Equalizer (EQ1, EQ2, EQ3, EQ4 and EQ5) is ON/OFF
independently by EQ1, EQ2, EQ3, EQ4 and EQ5 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. E4A15-0, E4B15-0 and E4C15-0
bits set the coefficient of EQ4. E5A15-0, E5B15-0 and E5C15-0 bits set the coefficient of EQ5. The EQx (x=1∼5)
coefficient should be set when EQx bit = “0” or PMADL=PMADR=PMDAL=PMDAR bits = “0”.
fs: Sampling frequency
fo1 ~ fo5: Center frequency
fb1 ~ fb5: Band width where the gain is 3dB different from center frequency
K1 ~ K5 : Gain (−1 ≤ Kn ≤ 3)
Register setting (Note 79)
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
EQ4: E4A[15:0] bits =A4, E4B[15:0] bits =B4, E4C[15:0] bits =C4
EQ5: E5A[15:0] bits =A5, E5B[15:0] bits =B5, E5C[15:0] bits =C5
(MSB=E1A15, E1B15, E1C15, E2A15, E2B15, E2C15, E3A15, E3B15, E3C15, E4A15, E4B15, E4C15,
E5A15, E5B15, E5C15; LSB= E1A0, E1B0, E1C0, E2A0, E2B0, E2C0, E3A0, E3B0, E3C0, E4A0, E4B0,
E4C0, E5A0, E5B0, E5C0)
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, 4, 5)
Transfer function
H(z) = 1 + h1(z) + h2(z) + h3(z) + h4(z) + h5(z)
1 − z −
2
hn (z) = An
1− Bnz −1− Cnz −2
(n = 1, 2, 3, 4, 5)
The center frequency should be set as below.
fon / fs < 0.497
Note 79. [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.
MS0963-E-00
2008/05
- 75 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
