AK4955 Datasheet, PDF (46/117 Pages) Asahi Kasei Microsystems – 24bit Stereo CODEC with MIC/SPK/Cap-less VIDEO-AMP/ LDO & DSP

[AK4955]
(5) 4-band Equalizer & 1-band Equalizer after ALC
This block can be used as equalizer or Notch Filter. 4-band equalizers (EQ2~EQ5) are switched ON/OFF independently
by EQ2, EQ3, EQ4 and EQ5 bits. EQ1 bit controls ON/OFF switching of the equalizer after ALC (EQ1). When the
equalizer is OFF, the audio data passes this block by 0dB gain. E1A15-0 bits, E1B15-0 bits and E1C15-0 bits set the
coefficient of EQ1. E2A15-0 bits, E2B15-0 bits and E2C15-0 bits set the coefficient of EQ2. E3A15-0 bits, E3B15-0 bits
and E3C15-0 bits set the coefficient of EQ3. E4A15-0 bits, E4B15-0 bits and E4C15-0 bits set the coefficient of EQ4.
E5A15-0 bits, E5B15-0 bits and E5C15-0 bits set the coefficient of EQ5. The EQx (x=1, 2, 3, 4 or 5) coefficient must be
set when EQx bit = “0” or PMPFIL bit = “0”. EQx starts operation 4/fs(max) after when EQx = PMPFIL bit = “1” is set.
fs: Sampling Frequency
fo₁ ~ fo₅: Center Frequency
fb₁ ~ fb₅: Band width where the gain is 3dB different from the center frequency
K₁ ~ K₅: Gain ( -1 ≤ K_n < 3 )
Register Setting (Note 42)
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 + G₂ x h₂(z) + G₃ x h₃(z) + G₄ x h₄(z) + G₅ x h₅(z)} x {1+ h₁(z) }
(G_{2, 3, 4, 5} = 1 or G)
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 42.
[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.
MS1343-E-00
- 46 -
2011/12