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[AK4675]
MS0963-E-00
2008/05
- 75 -
(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
fo
1
~ fo
5
: Center frequency
fb
1
~ fb
5
: Band width where the gain is 3dB different from center frequency
K
1
~ K
5
: Gain (
−
1
≤
K
n
≤
3)
Register setting (
EQ1: E1A[15:0] bits =A
1
, E1B[15:0] bits =B
1
, E1C[15:0] bits =C
1
EQ2: E2A[15:0] bits =A
2
, E2B[15:0] bits =B
2
, E2C[15:0] bits =C
2
EQ3: E3A[15:0] bits =A
3
, E3B[15:0] bits =B
3
, E3C[15:0] bits =C
3
EQ4: E4A[15:0] bits =A
4
, E4B[15:0] bits =B
4
, E4C[15:0] bits =C
4
EQ5: E5A[15:0] bits =A
5
, E5B[15:0] bits =B
5
, E5C[15:0] bits =C
5
(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)
A
n
= K
n
x
tan (
π
fb
n
/fs)
1 + tan (
π
fb
n
/fs)
B
n
= cos(2
π
fo
n
/fs) x
2
1 + tan (
π
fb
n
/fs)
, C
n
=
1
−
tan (
π
fb
n
/fs)
1 + tan (
π
fb
n
/fs)
,
(n = 1, 2, 3, 4, 5)
Transfer function
h
n
(z) = A
n
1
−
z
−
2
1
−
B
n
z
−
1
−
C
n
z
−
2
H(z) = 1 + h
1
(z) + h
2
(z) + h
3
(z) + h
4
(z) + h
5
(z)
(n = 1, 2, 3, 4, 5)
The center frequency should be set as below.
fo
n
/ 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 2
13
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.