Posted by
k6dgw on
Oct 05, 2010; 10:31pm
URL: http://elecraft.85.s1.nabble.com/K3-Clipping-vs-Compression-tp5605148.html
This was supposed to go to the reflector, sorry Joe.
I think top-post is the reflector standard, see below. I apologize, I
don't know who wrote what Joe quotes ...
I'm not sure I understand usage of the term "clipping" that has crept
into the "where's the punch" thread.
From my limited FM/AM/TV broadcast experience nearly a lifetime ago
while a college student, clipping and compression, at least then, were
two very separate things. Clipping referred to a [generally] unity gain
stage which at some output amplitude saturated heavily. Thus, up to
that point it was linear -- what went in came out. At saturation, there
was no increase in output amplitude regardless of input amplitude
increase. On the scope, the peaks just became flat. Our TV Stab Amps
[KSBY-TV] had a clipping stage to flatten the line-sync prior to the
keyed clamp stage which clamped the sync tips to a fixed level and
removed the DC drift as the video changed.
Compression was a variable gain amplifier. At very low input level, the
gain had some value which slowly decreased [usually linearly, sometimes
exponentially] as the input increased. The net effect was to decrease
the higher amplitudes in favor of the lower amplitudes, thus reducing
the dynamic range of the audio signal and raising the mean power. I
recall they came in several forms based on the time constant. The audio
chain on our AM transmitter [KVEC] included both a fast T-C and a very
long T-C [Sta-Level?] such that the dynamic range was very small and
everything was close to 100% modulation.
I could be wrong, it's happened a few times in the past, but I don't
think my K3 has a clipping stage, I think it is a classic variable-gain
compression stage which linearly reduces the dynamic range of the
modulating audio with increasing amplitude, with the first derivative of
the amplifier gain vs amplitude being adjusted by the CMP knob.
Feel free to correct me, as I said, it was nearly a lifetime ago, and
this really is a poorly worded question. Off the reflector might be a
good idea.
73,
Fred K6DGW
-- K3 #642
-- K2 # 4398
-- KX1 # 897
On 10/5/2010 12:43 PM, Joe Subich, W4TV wrote:
>
> > Now you have K3 users with no clue about how to set the TX eq and
> > clipping level OPTIONS to get the IDENTICAL shape to their
voices on a
> > K3 as the other rigs. There actually is a clarity advantage to the
> > K3's clipping method IF you know where to set all the options.
>
> How very true ...
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