BR262PMEVK
http://onsemi.com
3
Close-Talk Mixed 60% Towards Far-Talk
The second, mixed mode of close-talk mixed 60%
towards far-talk is similar to the core near-talk mode and
features excellent noise reduction in applications where the
speech source is located slightly further away from the
microphones; typically 50 to 100 cm. This mode is suitable
for handsfree devices and performs well in noise levels up
to 70 dB SPL. Expected noise reduction performance in this
mode is 10 to 20 dB SNR
−
I, depending on the type of noise.
Refer to the AND9109/D
−
BelaSigna R262 Getting
Started Guide for details on the different algorithm modes
and performance metrics.
Module Positioning
The speech source can come from any direction (normally
in front of the microphones), as long as it is within the
“working sphere” of the current algorithm mode. For
close-talk mode, the mouth reference point (MRP) should be
located between 5 and 10 cm from the microphones.
For close-talk mixed 60% towards far-talk, the MRP
should be located between 50 and 100 cm from the
microphones.
Acoustic Design
If the prototyping module is replacing an existing
microphone, the old microphone should be removed and the
module should be mounted as close as possible to the
original microphone location.
The device casing should be modified or manufactured
such that there is an appropriate acoustic path to the two
microphones on the module. Two holes roughly 0.5 to 1 mm
in diameter should be drilled in the casing 10 mm apart
above the sound ports of the onboard microphones. If
possible a rubber or foam isolation gasket should be installed
between the microphones and the device casing.
Electrical Considerations
The analog output(s) of the module can be connected
directly to any existing microphone input but keep in mind
that it may be necessary to lower any existing microphone
pre-amplification.
Care should be taken to properly shield the module and the
analog outputs if your product involves radio frequencies.
Use coaxial or shielded cable when connecting the analog
outputs of the module, and if necessary, wrap the module
with foil tape.
Customizing the Prototyping Module
If you would prefer to have the default tunings to be
something other than close-talk and close-talk mixed 60%
towards far-talk, you can change the values of the resistive
dividers on the BOOT_SEL (R3 and R4) and ALPHA_SEL
(R7 and R8) inputs. A component placement diagram
showing the locations of the various resistors is illustrated in
Figure 3. Refer to the BelaSigna R262 datasheet for more
information on BOOT_SEL and ALPHA_SEL inputs, and
the resistive divider values required to achieve specific
presets.
If you would like to re-configure the module to use the
DMIC interface, you must supply an appropriate DMIC
clock signal on the CLK test point and re-configure the
module’s CLOCK_SEL resistive divider (R1 and R2) to
match the provided clock frequency. A stereo DMIC signal
will be output on test point GP4. Refer to the
BelaSigna R262 datasheet for more information on the
supported DMIC clock frequencies, and the resistive divider
values required to select them.
If you would like to re-configure the module to output a
differential analog signal, you must adjust the resistive
dividers on the CHAN_SEL input (R5 and R6) to select
preset 0 or preset 5. Refer to the BelaSigna R262 datasheet
for more information on the CHAN_SEL input and the
resistive divider values required to achieve specific presets.
If you would like to re-configure the module to load a
custom application from the EEPROM, you must load a
valid custom application onto the EEPROM and remove
resistor R4 to have the module boot from EEPROM. Refer
to the BelaSigna R262 datasheet for more information on the
BOOT_SEL input and the resistive divider values required
to achieve specific presets. Contact your local
ON
Semiconductor support representative for more
information about custom applications.
