FROM: http://web.telia.com/~u85920178/use/filt2.htm

FROM: http://www.appliedphysicstech.com/CWF.html
CWF-001 Active CW Filter

FROM: http://www.morsex.com/misc/filter.htm
Vectronics CW Filter Kit with 1W Audio Amp

FROM: http://www.hanssummers.com/radio/cwfilter/index.htm
http://downloads.hanssummers.com/cwfilter.pdf
Phase-Shifting CW Filter by Radio Society of Great Britain


FROM: http://midnightscience.com/kits.html

HI-PER Audio Filter: 200 Hz wide; centered at 700 Hz Gausian active filter
with minimal group delay...no ringing... I have used this filter for over a decade
and it is very good with qrq cw. It is to be placed just before the final audio amp.
Please see the attached PDF file for the full article about it.

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Here is another CW AUDIO BANDPASS FILTER designed for listening to QRQ CW audio files

brief demo of using a Gstreamer 2 tiered CW AUDIO BANDPASS Filter for listening to CW AUDIO FILES from a CW Keyboard(AD5DZ)
The double filtering helps to get rid of virtual all of the CW ELEMENT percussive edge noise above and below the CW PITCH

using a simple Gstreamer script that includes 2 bandpass filters, staggered...1st step with a wider bandpass and lower Q than the 2nd... the filter can be adjusted to suit your own preferences for how "percussive" you want your own QRQ CW to sound...


GSTREAMER CW AUDIO BANDPASS 2 TIERED FILTER SCRIPT
***************************************************************
gst-launch-1.0 -v interleave name=i ! audioconvert ! queue ! deinterleave name=d d.src_0 ! queue ! audioconvert ! audiowsincband mode=band-pass lower-frequency=607 upper-frequency=807 length=200 window=hamming ! audioamplify amplification=11.7 ! jackaudiosink name=CWoutput buffer-time=30000 jackaudiosrc name=CWinput ! queue ! audiowsincband mode=band-pass lower-frequency=607 upper-frequency=807 length=100 window=hamming ! audioconvert ! queue ! i.

NOTE: this Gstreamer incorporates the Gstreamer 'interleave' and 'deinterleave' method to get both bandpass filters integrated

https://gstreamer.freedesktop.org/documentation/interleave/interlea...

https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugi...

NOTE: if your are using PULSEAUDIO you can still use this filter method by using one of the alsa loopback cables and say, FLdigi...FLDIGI OUTPUTS to an ALSA LOOPBACK...Gstreamer uses the output of the ALSA LOOPBACK as its "input" and then Gstreamer exits to the soundcard...(instead of using jackaudiosrc and jackaudiosink....try...pulsesrc & pulsesink and use the PAVUCONTROL to punch in the sound card output and the alsa loopback input for the Gstreamer input & output etc...

if you are using WINDOWS...instead of using ALSA LOOPBACK use a windows virtual audio cable..

if you are using MAC, use something like the soundflower virtual audio cable instead of alsa loopback

Here is a good example of a specialized CW FILTER using Gstreamer code for listening to QRQ CW on HF

using this Gstreamer code:
***************************
gst-launch-1.0 -v jackaudiosrc ! queue ! calf-sourceforge-net-plugins-eq5 ls-active=1 ls-level=0.015625 ls-freq=283.435 hs-active=1 hs-level=0.015625 hs-freq=1628.13 p1-active=1 p1-freq=305.818 p1-level=0.015625 p2-active=1 p2-level=63 p2-freq=678.284 p2-q=0.5 p3-active=1 p3-level=0.015625 p3-freq=1508.97 ! queue ! jackaudiosink buffer-time=15000

even at 400 hz bandwidth on the RIG's CRYSTAL RX filter..there is some annoying lower frequency wind tunnel like howling...that this filter minimizes, without effecting too much, the good sound of the QRQ CW being received

NOTE: this Gstreamer code uses a standard LV2 plugin - Calf 5 BAND EQ https://calf-studio-gear.org/

- many thanks to Bryan for providing the CW for this test -

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