[AK4679]
■ 5-Band Equalizer
The AK4679 has 5-Band Equalizer before DAC of Stereo CODEC. The 5-band Equalizer is selected ON/OFF by 5EQ
bit. When 5-band Equalizer is OFF, the audio data passes this block by 0dB gain. Each coefficient and transfer function of
5-band Equalizer is as follows. The coefficient must be set when 5EQ bit = “0” or PMEQ bit = “0”.
Gain range of 5-band equalizer is set from +12dB to -12dB (0.5dB step) independently by 5EQ1G5-0, 5EQ2G5-0,
5EQ3G5-0, 5EQ4G5-0 or 5EQ5G5-0 bits.
The 5-band Equalizer starts operation 4/fs(max) after when 5EQ bit = “1” and PMEQ bit = “1” is set.
1. EQ1: 1st order Low Pass Filter
<Low Pass Filter>
fs: Sampling frequency
fc: Cut-off frequency
k: Filter gain
Register setting (Note 78)
5E1A[13:0] bits =A, 5E1B[13:0] bits =B
(MSB=5E1A13, 5E1B13; LSB=5E1A0, 5E1B0)
1
1 − 1 / tan (πfc/fs)
1 + 1 / tan (πfc/fs)
A = k x
,
B =
1 + 1 / tan (πfc/fs)
Transfer function
1 + z −1
h1L (z) = A
1 + Bz −1
The cut-off frequency should be set as below.
fc/fs ≥ 0.05 (fc min = 2205Hz at 44.1kHz)
MS1402-E-06
2013/02
- 80 -
AKM [ ASAHI KASEI MICROSYSTEMS ]
