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K3 - Clipping vs Compression

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k6dgw

K3 - Clipping vs Compression

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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Joe Subich, W4TV-4

Re: K3 - Clipping vs Compression

Fred,

> 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.

I am very aware of the difference between clipping and compression.
I spent the majority of 20 years as a Director of Engineering in the
TV broadcast field and before that my early training was in recording
studios and radio production. I used clipping intentionally in my
posting. But if you don't believe me, please refer to the information
(test results) posted by Jack Smith, W8ZOA on his web site
<http://cliftonlaboratories.com/elecraft_k3_speech_processing.htm>
in which he characterized operation of the K3's audio processing.

Jack's analysis is: "This plot should immediately suggest that normal
audio compression is not used by the K3. The input-output curve slope
does not appreciably change with input signal for compression settings
between 0 and 30, and for compression settings of 35 and 40, extreme
slope changes are present."

Jack further reports information from Lyle Johnson, KK7P: "Lyle Johnson,
KK7P, of Elecraft confirmed in response to my question, that the K3
implements RF clipping, not audio compression. Accordingly, the
input-output transfer function does not appreciably change slope for
different compression setting values."

Thus, while the K3 Owner's Manual may refer to the audio processing
as "compression," in truth the DSP algorithm is really an envelope
(RF) clipper and the K3 behaves that way.

73,

... Joe, W4TV

On 10/5/2010 6:31 PM, Fred Jensen wrote:

> 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 ...
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html