[AK4679]
3. EQ5: 1st order High Pass Filter
<High Pass Filter>
fs: Sampling frequency
fc: Cut-off frequency
k: Filter gain
Register setting (Note 78)
5E5A[13:0] bits =A, 5E5B[13:0] bits =B
(MSB=5E5A13, 5E5B13; LSB=5E5A0, 5E5B0)
1 / tan (πfc/fs)
1 − 1 / tan (πfc/fs)
A = k x
,
B =
1 + 1 / tan (πfc/fs)
1 + 1 / tan (πfc/fs)
Transfer Function
1 − z −1
h5H (z) = A
1 + Bz −1
The cut-off frequency should be set as below.
fc/fs ≥ 0.0001 (fc min = 4.41Hz at 44.1kHz)
Note 78. [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.
Total Transfer Function:
H(z) = K1 x h1L(z) + K2 x h2(z) + K3 x h3(z) + K4 x h4(z) + K5 x h5H(z)
K1 ~ 5: EQ Gain (+12 ~ -12dB, 0.5dB step). This value is changed by control register.
K1: 5EQ1G5-0 bits (Addr=6AH)
K2: 5EQ2G5-0 bits (Addr=6BH)
K3: 5EQ3G5-0 bits (Addr=6CH)
K4: 5EQ4G5-0 bits (Addr=6DH)
K5: 5EQ5G5-0 bits (Addr=6EH)
Default Center Frequency (Sampling Frequency = 44.1kHz):
EQ1: fc=100Hz
EQ2: fo2=250Hz (fb2=50Hz)
EQ3: fo3=1kHz (fb3=200Hz)
EQ4: fo4=3.5kHz (fb4=700Hz)
EQ5: fc=10kHz
MS1402-E-06
2013/02
- 82 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
