[AK4634]
(3) 5-band Equalizer
This block can be used as Equalizer or Notch Filter. ON/OFF 5-band Equalizer (EQ1, EQ2, EQ3, EQ4 and EQ5) can be
controlled 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.
fs : The Sampling frequency
fo1 ~ fo5 : The Center frequency
fb1 ~ fb5 : The Band width where the gain is 3dB different from center frequency
K1 ~ K5 : The Gain ( -1 ≤ Kn < 3 )
Register setting (Note 30)
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
When gain of K is set to “−1”, the equalizer becomes notch filter. The central frequency of a real notch filter deviates from
the above calculation, if the central frequency of each band is near. The control soft that is attached to the evaluation board
has a function that revises a gap of frequency, and calculates the coefficient. When the central frequency of each band is
near, revise the central frequency and confirm the frequency response.
Note 30.
[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.
MS0983-E-00
2008/07
- 40 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
