[Elecraft] [K3] Rx Equalizer

[Lyle Johnson]

> I learned last week after experiencing less than optimal
> FM audio quality on receive that the Rx EQ is enabled
> on all modes. I've never seen that on FM. 

The Rx EQ is for the receiver. It currently applies to all modes.

> The complicating factor is that the 8 equalizer sound
> band values vary from the K3 documentation whenever the 
> filter width changes (this always happens with
> mode changes). 

There is but one Rx EQ routine in the DSP and it has but one set of 
parameters. It does not vary by mode; it is completely independent.

Note that the way the EQ works is that it creates, or attempts to 
create, a smooth slope from the indicated frequency (say, 1.60 kHz, EQ 
band 6) to halfway to the next indicated frequencies (in this case, 
halfway to the 0.80 kHz band (thus 1200 Hz), band 5) and halfway to the 
2.40 kHz band (thus 2.00 kHz), band 7).

The Tx EQ works the same way.  This is similar to the way the W2IHY 
equalizer works,or the formerly-common "graphic equalizer" sliders on 
stereo equipment.  The indicated frequency is the "center" of the band 
of frequencies over which it operates.  (I put "center" in quotes as you 
may not consider 1600 Hz to be the center frequency between 1200 Hz and 
2000 Hz as explained above.)

Finally, the upper frequency correction value (3200 Hz, band 8) extends 
to the top of the audio passband.  If you set it for - 4 dB, for 
example, the -4 dB correction will be applied from 3.20 kHz to 4 kHz, or 
4.2 kHz, or whatever the audio frequency cutoff happens to be for the 
mode you have selected.

The net result is that you can create a smooth frequency roll off 
characteristic.

While on the topic of the ERQ, some people have asked me if the DSP 
delay can be reduced if the EQ is set to OFF (flat).

The answer is no.

The Rx EQ is *not* a separate process added to the audio path.  The EQ 
parameters are used when building the AF filter response for the radio. 
  There is *one* DSP AF filter, which includes the effects of 
SHIFT/WIDTH/MANUAL NOTCH *and* Rx EQ.

The Auto notch, and noise reduction, are additional processes in the 
path.  So is AFX in the right channel.

73,

Lyle KK7P