[arm-allstar] Interesting info on the new hamvoip lowpass filter

[Doug Crompton]

This was mentioned before but not to any great detail. If you are using the
hamvoip V1.5 image v1.5.3-32 5/28/2018 or later your image has the new
brick-wall low-pass filter. The low-pass filter has a corner frequency at
3.5KHz, with all components at least -50dB down at 4KHz and above. This
filter is always on and adds the most fidelity that you can get at an 8Khz
sample rate.

Here is an image of the new Low Pass filter:
https://hamvoip.org/docs/FIR-LP-simpleusb-2018-05-27-1.png

This filter eliminates the need for any hardware filtering in FOBS so the
"fancier" FOB's with hardware low-pass filtering like the DMK-URI and
others are not needed to achieve this well filtered and excellent audio.
Using this software and the filter means you no longer have to worry about
out of band audio components when using the cheaper FOB's without any
hardware low-pass filtering.


*73 Doug*

*WA3DSP*

*http://www.crompton.com/hamradio <http://www.crompton.com/hamradio>*