Datasheet
MAX9867
Ultra-Low Power Stereo Audio Codec
34 ______________________________________________________________________________________
Digital Filtering
The MAX9867 incorporates both IIR (voice) and FIR
(audio) digital filters to accomodate a wide range of
audio sources. The IIR fiilters provide over 70dB of
stopband attenuation as well as selectable highpass fil-
ters. The FIR filters provide low-power consumption and
are linear phase to maintain stereo imaging. Table 7 is
the digital filtering register.
REGISTER B7 B6 B5 B4 B3 B2 B1 B0
REGISTER
ADDRESS
Codec Filters MODE AVFLT 0 DVFLT 0x0A
BITS FUNCTION
MODE
Digital Audio Filter Mode
0 = IIR Voice Filters
1 = FIR Audio Filters
AVFLT
ADC Digital Audio Filter
MODE = 0
Select the desired digital filter response from Table 8. See the Frequency Response graph in the Typical
Operating Characteristics section for details on each filter.
MODE = 1
0x0 = DC-blocking filter is disabled. Any other setting = DC-blocking filter is enabled.
DVFLT
DAC Digital Audio Filter
MODE = 0
Select the desired digital filter response from Table 8. See the Frequency Response graph in the Typical
Operating Characteristics section for details on each filter.
MODE = 1
0x0 = DC-blocking filter is disabled. Any other setting = DC-blocking filter is enabled.
Table 7. Digital Filtering Register
CODE FILTER TYPE
INTENDED SAMPLE
RATE (kHz)
HIGHPASS CORNER
FREQUENCY (Hz)
217Hz NOTCH
0x0 Disabled
0x1 Elliptical 16 256 Yes
0x2 Butterworth 16 500 No
0x3 Elliptical 8 256 Yes
0x4 Butterworth 8 500 No
0x5 Butterworth 8 to 24 f
S
/240 No
0x6 to 0x7 Reserved
Table 8. IIR Highpass Digital Filters