[Elecraft] K3 Audio Low Pass Filter

[n7ws at yahoo.com]

--- On Sat, 7/4/09, Mike Scott <mike at paxsen.com> wrote:

Mike,
I am still evaluating but I believe the LP filter took the harshness out of
my audio. I had been one of people with a complaint about harsh audio and so
far I like it. I seem to have distortion products above the intended audio
passband that this filter cuts out. That extra stuff made it fatiguing for
me; other people don't hear it. I understand that some people can be
fatigued by odd order harmonic distortion even when the distortion is way
down.

Absolutely.  There is simply no excuse for the levels of audio distortion that exists in some modern receivers.  IMHO, distortion not only adds to fatigue, but negatively affects intelligibility, particularly on weak signals buried in noise, such as those on EME.

It seems to me that since audio is the desired output, the design process should be to design an excellent audio system first and then work back toward the antenna.  Regrettably, it seems this is the converse of how it works and the audio system becomes an afterthought, with some designers believing that <10% THD is "good enough" for "communications" audio.