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

using this Gstreamer code:
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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 -

Square Wave to SiNE WAVE CW audio filter converter using a large FERRiTE ROD double tuned to 800 hz

series resonated by CAP to FERRITE ROD primary

parallel resonated by CAP to FERRITE ROD secondary

using a SERIES (input)/ PARALLEL(output) , CAPACITOR {double tuned}, 732 hertz, step down transformer,  gives over a 3 db boost in sound output from a speaker - even just using a sound card's LINE OUTPUT gets almost 90 db of PURE SINE WAVE CW sound out of a cheap radio shack speaker, using an adjustable BASS tuning PORT(also adjusted to resonate at 732 hertz)

[NO EXTERNAL AMP IS NEEDED   90 db  of  CW AUDIO VOLUME is enough

                                                                to be heard throughout the whole house]

NOTE:  Transformer primary = 400 turns,  2ndary = 52 turns,  has a large ferrite core that is

14 inches in length and 1 1/4 inch in diameter 

HERE IS THE READOUT withOUT using the STEP DOWN TRANSFORMER:

HERE IS THE SOUND DECIBEL readout WHEN using this large CUSTOM WOUND step down transformer:

DOUBLING THE AUDIBLE VOLUME OUTPUT from this RADIO SHACK SPEAKER