[Elecraft] K3 Audio Low Pass Filter

[Brett Howard]

I did an A/B test with before and after measurements at the speaker out
port.  The difference in the VERY high frequency where that drop off
occurs is because of a sample rate difference and should make no
difference in the lower frequency information.  The wide band plot makes
it pretty obvious what the filter is designed to take out around 11 to
13 Khz or so...

Anyway hope this clears things up a bit as to what its designed to do.
it gives a much beloved openness and clarity to the sound.  I had no
problems spending a good long time behind the radio at FD.  I think I
was behind that thing from 11 to 3AM with only very short breaks.

~Brett

On Sat, 2009-07-04 at 10:20 -0700, Mike Scott wrote:
> >G'day,
> >What about - how did it perform?
> >...does it in any way respond to the "pink" vs. "white" noise thread of a
> few weeks ago.
> >Mike VP8NO
> 
> 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.
> 
> I am not set up to compare with another radio and I can't do an A-B test as
> the filter is hardwired in. I plan to live with this set up for a while and
> maybe put in larger coupling caps to bring up the audio warmth. Perhaps I
> will replace with 100 uF SMD devices like the current production caps.
> 
> The filter is a 4th order Chebyshev low pass filter with a -6dB shoulder
> somewhere around 4.5 KHz judging by looking at a plot. It is flat below 3.2
> KHz and low ripple, so, nothing to do with pink noise. Maybe Wayne will get
> around to putting a pink noise filter into the DSP.
> 
> I am experimenting with the following Rx EQ settings from another post to
> simulate a pink noise filter:
> 1 +0
> 2 +8
> 3 +2
> 4 -1
> 5 -1
> 6 -3
> 7 -5
> 8 -10
> 
> 
> 
> Mike Scott - AE6WA
> Tarzana, CA (DM04 / near LA)
> NAQCC 3535
> K3-100 #508 / KX1  #1311
> 
> 
> 
> 
> 
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