wm8918 Wolfson Microelectronics plc, wm8918 Datasheet - Page 44

• Manufacturer Part Number: wm8918
• Description: Ultra Low Power Dac For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

WM8918
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HIGH PASS FILTER
A digital high pass filter is applied by default to the DMIC path to remove low frequency noise in voice
applications (e.g. wind noise or mechanical vibration). This filter is controlled using the DMIC_HPF
and DMIC_HPF_CUT register bits.
In hi-fi mode the high pass filter is optimised for removing DC offsets without degrading the bass
response and has a cut-off frequency of 3.7Hz at fs=44.1kHz.
In voice mode the high pass filter is optimised for voice communication and it is recommended to
program
DMIC_HPF_CUT=10 at fs=16kHz).
Table 11 DMIC Digital 0 Register
Table 12 DMIC High Pass Filter Cut-Off Frequencies
The high pass filter characteristics are shown in the “Digital Filter Characteristics” section.
R38 (26h)
DMIC Digital
0
REGISTER
Frequency
ADDRESS
Sample
11.025
16.000
22.050
24.000
32.000
44.100
48.000
(kHz)
8.000
the cut-off frequency below 300Hz (e.g. DMIC_HPF_CUT=11 at fs=8kHz or
DMIC_HPF_CUT
BIT
6:5
4
=00
0.7
0.9
1.3
1.9
2.0
2.7
3.7
4.0
DMIC_HPF_C
DMIC_HPF
UT [1:0]
LABEL
DMIC_HPF_CUT
DEFAULT
CUT-OFF FREQUENCY (Hz)
=01
127
175
190
253
348
379
64
88
00
1
DMIC Digital High Pass Filter Cut-Off
Frequency (fc)
00 = Hi-fi mode (fc=4Hz at fs=48kHz)
01 = Voice mode 1 (fc=127Hz at
fs=16kHz)
10 = Voice mode 2 (fc=130Hz at fs=8kHz)
11 = Voice mode 3 (fc=267Hz at fs=8kHz)
(Note: fc scales with sample rate. See
Table 12 for cut-off frequencies at all
supported sample rates)
DMIC Digital High Pass Filter Enable
0 = Disabled
1 = Enabled
DMIC_HPF_CUT
=10
130
178
258
354
386
514
707
770
PD, Rev 4.0, September 2010
DESCRIPTION
DMIC_HPF_CUT
Production Data
1063
1464
1594
=11
267
367
532
733
798
44