[AK4753]
■ Five Programmable Biquads
This block can be used as an 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 the equalizer is OFF, the audio data passes this block by
0dB gain. E1A19-0, E1B19-0 and E1C19-0 bits set the coefficient of EQ1. E2A19-0, E2B19-0 and E2C19-0 bits set the
coefficient of EQ2. E3A19-0, E3B19-0 and E3C19-0 bits set the coefficient of EQ3. E4A19-0, E4B19-0 and E4C19-0
bits set the coefficient of EQ4. E5A19-0, E5B19-0 and E5C19-0 bits set the coefficient of EQ5. EQx (x=1~5)
coefficient should be set when EQx bit = “0” or PMDAC bit = “0”. When the SA2 bit = “1”, K1 gain must be set to “1”
for the DSP channel selected by the SA2SEL bit.
fs: Sampling frequency
fo1 ~ fo5: Center frequency
fb1 ~ fb5: Band width where the gain is 3dB different from center frequency
K1 ~ K5 : Gain ( -1 ≤ Kn < 3 )
Register setting (Note 22)
EQ1: E1A19-0 bits =A1, E1B19-0 bits =B1, E1C19-0 bits =C1
EQ2: E2A19-0 bits =A2, E2B19-0 bits =B2, E2C19-0 bits =C2
EQ3: E3A19-0 bits =A3, E3B19-0 bits =B3, E3C19-0 bits =C3
EQ4: E4A19-0 bits =A4, E4B19-0 bits =B4, E4C19-0 bits =C4
EQ5: E5A19-0 bits =A5, E5B19-0 bits =B5, E5C19-0 bits =C5
(MSB=E1A19, E1B19, E1C19, E2A19, E2B19, E2C19, E3A19, E3B19, E3C19, E4A19, E4B19, E4C19, E5A19,
E5B19, E5C19; LSB= E1A0, E1B0, E1C0, E2A0, E2B0, E2C0, E3A0, E3B0, E3C0, E4A0, E4B0, E4C0, E5A0,
E5B0, E5C0)
2
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)
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 fbn should be set within the range as follows.
fbn/fs ≤ 0.25
The f0n (center frequency) should be set within the range as follows.
3.125x10-3 ≤ f0n/fs < 0.4969
When the f0n/fs is less than 3.125x10-3, the step width of the f0n which can be set up becomes the biggest in the case of
fbn/fs=0.25. (Table 30)
f0n/fs
8.542x10 -4
1.083x10 -3
1.229x10 -3
:
f0n(@fs=48kHz)
An (dec) (Kn=-1)
-65536
-65536
-65536
:
Bn (dec)
131070
131069
131068
:
Cn (dec)
41Hz
52Hz
59Hz
:
0
0
0
:
3.125x10 -3
150Hz
-65536
131047
0
Table 30. The Center Frequency in the low frequency band
(when the coefficients of An, Bn and Cn is fbn/fs=0.25)
Note 22. 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 217
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 sign bit.
MS1311-E-00
2011/07
- 43 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
