wm8400 Wolfson Microelectronics plc, wm8400 Datasheet - Page 73

• Manufacturer Part Number: wm8400
• Description: Wolfson Audioplustm Hi-fi Audio Codec And Power Management Unit For Mobile Multimedia
• Manufacturer: Wolfson Microelectronics plc

w
Pre-Production
HIGH PASS FILTER
A digital high pass filter is applied by default to the ADC path to remove DC offsets. This filter can
also be programmed to remove low frequency noise in voice applications (e.g. wind noise or
mechanical vibration). This filter is controlled using the ADC_HPF_ENA and ADC_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
ADC_HPF_CUT=10 at fs=16kHz).
Table 35 ADC High Pass Filter Control Registers
Table 36 ADC High Pass Filter Cut-Off Frequencies
The high pass filter characteristics are shown in the "Digital Filter Characteristics" section.
FREQUENCY
R15 (0Fh)
REGISTER
ADDRESS
SAMPLE
11.025
16.000
22.050
24.000
32.000
44.100
48.000
8.000
(kHz)
the
8
6:5
cut-off
BIT
ADC_HPF_CUT
ADC_HPF_ENA
ADC_HPF_CUT
[1:0]
=00
0.7
0.9
1.3
1.9
2.0
2.7
3.7
4.0
frequency
LABEL
below
ADC_HPF_CUT
CUT-OFF FREQUENCY (Hz)
1b
00b
DEFAULT
127
175
190
253
348
379
=01
64
88
300Hz
(e.g.
ADC Digital High Pass Filter Enable
0 = disabled
1 = enabled
ADC 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 36 for cut-off frequencies at all
supported sample rates)
ADC_HPF_CUT
ADC_HPF_CUT=11
130
178
258
354
386
514
707
770
=10
DESCRIPTION
ADC_HPF_CUT
PP, April 2009, Rev 3.0
1063
1464
1594
267
367
532
733
798
=11
at
WM8400
fs=8kHz
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or