[Elecraft] CESSB (was Re: Software Update for KX3)

[Jim Brown]

On 7/20/2025 3:12 PM, QRP Labs via Elecraft wrote:
>   This is
> important because often people are using compression and without realizing
> that due to the SSB overshoot problem, the ALC now has to reduce the gain
> even more to avoid the splatter. In other words some of the dB you got by
> using compression, you give back because the ALC had to more aggressively
> reduce it due to higher envelope overshoots; but with CESSB you get to keep
> all the compression dB advantages (plus the regular advantage of CESSB).

Good points, Hans. But the important thing to realize, though, is that 
audio is a very complex signal, whose spectral distribution, is 
approximately logarithmic, as is the human ear/brain hearing system. And 
as more than a century of studies of how we hear, engineers learned that 
components of speech below about 500 Hz contribute almost nothing to 
speech intelligibility, and while components above about 3 kHz do help 
some, we can do quite well without them and save a lot of bandwidth (and 
transmitter power).

Bottom line is that steady state measurements of anything involving 
audio are pretty meaningless. We can define system clip and assess the 
noise floor, but that's about it. Two-tone tests for IMD tell us next to 
nothing about what happens with program material.

I determine the cleanliness of transmitters by accumulating peaks on a 
system like the P3 that shows the spectrum, and by looking for 
horizontal overshoots on a waterfall. I study key clicks in the same 
way, not by looking at square waves on a scope. I learned most of what I 
know about audio measurements under Dick Heyser, the inventor of TDS 
(Time Delay Spectrometry), and used it extensively in my consulting 
practice.

73, Jim K9YC