LF: DSP-filter for aural CW

[Dick Rollema <dickrollema@casema.nl>]

To All from PA0SE

Does someone know whether a DSP filter using the sound card of the computer 
can be found on the internet , that can filter the audio output of the 
receiver with an adjustable bandwidth down to, say, 20Hz or so?
I use a passive audiofilter between the receiver and the headphones with 
four tuned circuits. It has a bandwidth of about 25Hz, a centre frequency 
of 900Hz and a linear phase characteristic to avoid ringing.  But perhaps a 
DSP filter could do even better.
73, Dick, PA0SE
JO22GD