[Elecraft] K3 SSB Contour Filter (reduce total bandwidth)

[Joe Subich, W4TV]

Tony, 

> 	I have not had time to give it a good test. The noise 
> reduction of the narrower bandwidth is not significant but 
> annoyance of the band noise in the gap is eliminated. It is 
> debatable whether the built in NR is better.
>	I think filter settings need to be set up with macros. 
> Manual adjustment in the heat of the battle is way too slow. 
> I suggested before that maybe the XFIL (or SPOT or CWT) which 
> are not used on SSB could be used for customizable filter 
> settings (in sequence).

I played around with the RX EQ and manual notch a bit the other 
day trying to simulate a SSB contour filter.  The experiments 
lead to a couple of ideas for Lyle to play with .... 

1) "Dual PB" is not operational in SSB ... how about an overlay 
   filter than simply provides a broad 25 to 30 dB notch  from 
   800Hz to 1300 Hz?  

   The depth and exact width might be fertile ground for some 
   further experimentation but it is this 800-1300 Hz area (+/- 
   100 Hz on either end) that lacks voiced energy in human 
   speech.  Fundamental, second and third harmonics generally 
   exist below 800 Hz (up to 1000 Hz in some female voices) 
   while the sibilance generally begins in the range above 
   1500 Hz.  

2) Since the 50 Hz band of the RX EQ has very little if any 
   effect even when the audio response is extended down to 
   100 Hz, eliminate that band and add a new band at 1200 Hz. 
   In addition, extend the range of "cut" available to -30 dB 
   (from -16 dB).  

   With the additional capabilities, the user can use RX EQ 
   to create his own "SSB contour" filter by dialing in as 
   much or little cut at 800 and 1200 Hz as is appropriate. 

> Ignoring the bandwidth for the moment, the question becomes, 
> "Is the resulting voice signal acceptable under crowded band 
> conditions?"

Lyle, on receive it's possible to demonstrate some of the benefit 
of a "voice contouring filter" simply by setting the 800 Hz RX EQ 
to -16 dB and the manual notch to 1100 or 1200 Hz.  

Audio engineers have made use of a 1000 - 1200 Hz notch for many 
years to make band limited audio sound less muffled and make 
voices more intelligible.  

73, 

   ... Joe, W4TV