K3: noise reduction performance

Posted by K2QI on Nov 27, 2010; 12:16pm
URL: http://elecraft.85.s1.nabble.com/K3-noise-reduction-performance-tp5779574.html

Hello Elecrafters,

Regarding the issue of NR, I know this can be a touchy subject and most will
say its very subjective.  This post isn't intended as a complaint or
criticism.  Instead, I hope through constructive discussions, more
improvements to the K3's NR performance will be realized. I'd like to begin
by saying that Lyle and crew have a done a fantastic job to date with the
K3's NR.  I've had the privilege of watching the K3's NR function improve
over time.  The boys at Aptos should really be commended for listening to
their customers.

With that said, the recent CQSS has made me realize that there is still room
for improvement.  During the SS, I used NR extensively in combination with
RF gain and filter hi-cut/lo-cut/shift settings.  NR when used in
combination with the aforementioned K3 adjustments can and does work well.
 The problem that I believe remains however is the algorithm used still
seems too broad in its rejection calculations; what I mean is that SSB
settings (i.e. F5-1 and higher) don't seem to be selective enough to reduce
noise while allowing speech patterns to remain unaffected.  In other words,
the DSP sounds like its reducing everything within its passband.  To my
ears, the NR doesn't seem to make speech "pop out" quite as effectively has
other NR implementations.  This can be seen by a not-so-subtle reduction in
speech volume whenever the NR is turned on.   The NR behavior is consistent
regardless of AGC slope or threshold settings.

Below are several links to audio recordings of a product I used to own.  It
is called the BHI ANEM (Mk. II). Sadly, I sold it after getting the K3.  I
should have hung on to it as it has become my benchmark for NR performance.

These are some sample recordings of the ANEM being turned on and off.  These
recordings are found on W4RT's website

20 m SSB <http://www.w4rt.com/BHI/20Mband-ssb.wav>
80 m SSB <http://www.w4rt.com/BHI/80conv-ssb.wav>
80 m SSB <http://www.w4rt.com/BHI/80Mconv2-ssb.wav>

I've also compared the K3's NR performance to that of the Icom 756 Pro 3
which has similar NR reduction properties - albeit not as effective - as the
ANEM.

Perhaps I am being subjective or overly critical, but one thing you can
easily notice with the ANEM recordings is that speech volume doesn't get as
affected as the K3s.  This is really surprising to me as the NR for the ANEM
is AF rather than IF like what's used in our radios.  This leads me to
believe that the ANEM's NR algorithms are more effective in reducing
background noise while leaving speech unaffected.

What do you guys think?

Sorry for the long email. Many thanks in advance for your ideas/suggestions.
<http://www.w4rt.com/BHI/20Mband-ssb.wav>
--
73 de James K2QI
President UNARC/4U1UN
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