The DSP Audio Filter is a tool that enables you to filter frequencies
from an audio spectrum by using your cell phone’s microphone.

This app was originally programmed for Ham Radio (Amateur Radio)
operators to remove unwanted background noise and improve SSB and CW
signals (Morse Code) but it can be used in different other ways.
For Example:
-Bird watchers can use it to filter out higher frequencies and eliminate street noise or other disturbing low frequencies.
-Musicians can filter out a spectrum of specific instruments.

 The DSP Audio filter uses a freely adjustable lowpass and highpass
filter which allows you to select specific filter frequencies and
bandwidths. A waterfall visually displays the incoming audio spectrum to
better identify the wanted or unwanted frequencies. You must use a
headphone to avoid feedback effects.
Ham Radio Operator’s: Just place your phone’s microphone close to your
radio’s speaker and listen to clear audio in your headphone.

How to use:

DSP Audio Filter uses a waterfall to display the incoming frequency
spectrum. With 2 sliders the cut-off frequencies can be adjust. The
areas which are covered by a grey blurry layer are cut out and they will
not be passed through to the headphone. All other areas will pass the
filter.

The DSP Audio Filter can be used with 4 different sampling rates
(22050Hz, 16000Hz, 11025Hz and 8000Hz) which can be set in the settings
menu. Unfortunately not all devices support those sampling rates. The
DSP Audio Filter will check for the supported sampling rates and only
allows the selection of the supported sampling rates.

By 9M2PJU

Amateur radio operator from Malaysia

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