AK4649 Datasheet, PDF (43/96 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK-AMP

[AK4649]
(5) 4-band Equalizer & 1-band Equalizer after ALC
This block can be used as Equalizer or Notch Filter. 4-band Equalizer (EQ2, EQ3, EQ4 and EQ5) is selected ON/OFF
independently by EQ2, EQ3, EQ4 and EQ5 bits. The equalizer after ALC (EQ1) is controlled by EQ1 bit. 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 must be set when EQx bit = “0” or PMPFIL bit = “0”. EQ1-5 start
operation 4/fs(max) after when EQx (X=1~5) = PMPFIL bit = “1”is set.
fs: Sampling frequency
fo₁ ~ fo₅: Center frequency
fb₁ ~ fb₅: Band width where the gain is 3dB different from center frequency
K₁ ~ K₅: Gain (−1 ≤ K_n ≤ 3)
Register setting (Note 36)
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)
A_n = K_n x
tan (πfb_n/fs)
1 + tan (πfb_n/fs)
(n = 1, 2, 3, 4, 5)
, B_n = cos(2π fo_n/fs) x
2
1 + tan (πfb_n/fs)
, ^{Cn =}
1 − tan (πfb_n/fs)
1 + tan (πfb_n/fs)
Transfer function
H(z) = {1 + h₂(z) + h₃(z) + h₄(z) + h₅(z) } x {1+ h₁(z)}
h_n (z) = A_n
1 − z ^−2
1− B_nz ^−1− C_nz ^−2
(n = 1, 2, 3, 4, 5)
The center frequency must be set as below.
fo_n / fs < 0.497
When gain of K is set to “-1”, this equalizer becomes a notch filter. When EQ2 ∼EQ5 is used as a notch filter, central
frequency of a real notch filter deviates from the above-mentioned calculation, if its central frequency of each band is near.
The control soft that is attached to the evaluation board has functions that revises a gap of frequency and calculates the
coefficient. When its central frequency of each band is near, the central frequency should be revised and confirm the
frequency response.
Note 36. [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 must 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.
MS1023-E-01
- 43 -
2010/08