[Elecraft] SHIFT pitch

[Don Wilhelm]

Doug,

I always use the HiCut/LoCut for SSB and just forget about the NORM 
settings.
The center frequency will be automatically set and it is quick to turn 
the HI knob just enough to reduce interference - the roofing filters 
will switch in automatically as required to support the DSP bandwidth.

If you listen to a SSB signal and try using the LO and HI CUT knobs, you 
should observe that you can cut a lot at the high end, but not much can 
be cut on the low end without loosing intelligibility.

I agree it is a pain to maintain intelligibility for a voice signal when 
using the WIDTH and SHIFT controls - every time the width is changed, 
the shift must be adjusted to maintain a usable speech response - it is 
a requirement, just like you indicated.
If you look at the frequency content of a human voice, you will find 
that there must always be energy in the 300 to 500 Hz range to maintain 
intelligibility.  If you have a 2.2 kHz filter set that extends from 300 
Hz to 2500 Hz (filter center 1.4), and you narrow that using the width 
control to 1.8 kHz, the filer center will stay at 1.4 kHz, and the 
filter will span from 500 Hz to 2.3 kHz - the important portion of the 
signal at 300 to 500 Hz will be gone, and the passband must be 
re-centered at 1.2 kHz to gain it back.

I believe it is much easier to set the LoCut somewhere in the 200 to 350 
Hz range (let's assume it is set at 300 Hz).  For a 2.2 kHz filter 
width, set the HiCut to 2.5 kHz.  If you then move the HiCut down to 2.1 
kHz, the filter width is now 1.8 kHz and intelligibility is maintained - 
if you have the 1.8 kHz roofing filter installed, it should be switched 
in automatically when the width is reduced to 1.8 kHz either by using 
the HiCut or the WIDTH control.  One does not have to do the addition 
and subtraction to determine the filter width at all - just change the 
HI CUT knob until the QRM is reduced sufficiently - move LO CUT a little 
if that is necessary too, but do it while listening to the signal, you 
will know when the desired signal becomes unintelligible.

Try it - if your narrow filters do not switch in automatically when 
using only the HiCut, there is something wrong.  Let the DSP do the math 
for you, it is much faster at that task than either of us are.

73,
Don W3FPR

GM0ELP wrote:
> Hi,
> I find that shift has to be reduced progressively as width is reduced on SSB
> eg.
>
> 2.7KHz width  *1.5KHz shift
> 2.1KHz *1.25KHz shift
>
> As I decrease the WIDTH past my 2.1KHz roofing filter with DSP, I constantly
> adjust SHIFT downwards to achieve normal sounding audio eg.
>
> 1.8KHz 1.1KHz shift
>
> I asked Lyle about it and he said that for SSB, LO and HIGH CUT should be
> used instead of WIDTH for SSB. WIDTH is meant for narrow bandwidth modes
> i.e. CW.
>
> Personally I find LO and HIGH cut arkward to use, especially when you have
> optional roofing filters installed. This is because the primary function of
> NORM is overloaded to automatically select the 2.7KHz roofing filter???. The
> secondary function of NORM (I/II) means you can have a some defaults, but
> try remembering what's behind them in the middle of a contest (if you get
> enough time to select them).
>
> It would be nice if the primary function of NORM just normalised the current
> filter width around the current shift value.
>
> Doug GM0ELP
>
>   
>