WM8961
Pre-Production
ADC DIGITAL FILTERS
The ADC filters perform true 24-bit signal processing to convert the raw multi-bit over-sampled data
from the ADC to the correct sampling frequency to be output on the digital audio interface.
ADC 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 can be disabled using the ADCHPD register bit. The cut-off frequency of the filter is
controlled by ADC_HPF_CUT.
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 the cut-off frequency below 300Hz (e.g. ADC_HPF_CUT=11 at fs=8kHz or
ADC_HPF_CUT=10 at fs=16kHz)
REGISTER
ADDRESS
BIT
LABEL
ADCHPD
DEFAULT
DESCRIPTION
R5 (05h)
ADC and DAC
Control (1)
0
0
ADC High Pass Filter Disable
0 = Enable high pass filter on left and
right channels
1 = Disable high pass filter on left and
right channels
8:7
ADC_HPF_CUT[ 00
1:0]
ADC High Pass Filter Cutoff
00: Hi-fi mode (fc=4Hz at fs=48kHz)
01: Voice mode 1 (fc=127 at
fs=16kHz)
R6 (06h)
ADC & DAC
Control 2
10: Voice mode 2 (fc=130 at
fs=8kHz)
11: Voice mode 3 (fc=267Hz at
fs=8kHz)
(Note: fc scales with sample rate.
See Table 14 for cut-off frequencies
at all supported sample rates)
Table 13 ADC High Pass Filter
SAMPLE
CUT-OFF FREQUENCY (HZ)
FREQUENCY
ADC_HPF_CUT
ADC_HPF_CUT
=01
ADC_HPF_CUT
=10
ADC_HPF_CUT
=11
(KHZ)
=00
8.000
11.025
16.000
22.050
24.000
32.000
44.100
48.000
0.7
0.9
1.3
1.9
2.0
2.7
3.7
4.0
64
130
178
258
354
386
514
707
770
267
367
88
127
175
190
253
348
379
532
733
798
1063
1464
1594
Table 14 ADC High Pass Filter Cut-Off Frequencies
The high pass filter characteristics are shown in the “Digital Filter Characteristics” section.
PP, August 2009, Rev 3.1
w
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
