Hello All,
I have had a few reports from customers that the receive audio sounds just
the same as it did before regardless of QRN or impulse noise.
Well, let's look at those "same as before" customers specifically.
This set of customers ran the HW Noise Blanker on all of the time anyway
just because they liked how it sounded with it on.
That is fine, but, remember what the change for AGC and QRN / impulse noise
really fixed.
In the previous release, WHEN there was QRN or Impulse Noise or ignition or
whatever, the AGC would falsely load up bringing audio level way way down
in an instant, and then return after a second or so, making it interesting
to copy or understand when there was QRN or impulse noise.
These customers, by keeping HW NB on all of the time, were taking out the
QRN before it ever made it to the DSP.
So, no QRN to react to, this meant no loading up of the AGC.
So, for them, this change, was almost a "no change".
For others, who never use the Software Noise Blanker or the Hardware Noise
Blanker, the reports are that the audio doesn't load up anymore, but they
hear the QRN or impulse noise.
Well, the answer to that is, in my opinion... turn on the HW Noise Blanker.
Then you won't hear the QRN.
There are other techniques, e.g. Orion and Orion II users have the SAF
feature that they can turnon, which can be dialed up to "boost" the audio
in the "audible tones" area that they want to listen to, and in a lot of
cases, the extra qrn/crap will get attenuated, not always, but some of the
time.
A word about Noise featuring.
They all work on different types of noise differently.
Noise Blanker
This is meant to work on impulse noise, stuff that is very short (VERY
short duration), and sometimes very dramatic in amplitude versus the normal
audio/noise floor. It is very aggressive and things that pop up very
quickly and go away that are dramatic, get removed. The Software Noise
Blanker in the Orion I/II and OMNI-VII are adjustable in their
aggressiveness. The Software Noise Blanker is one of the first things done
to the signal, and works on IF BEFORE AGC is applied. Hence, previous
builds, if SW NB was turned on, AGC would not load up on QRN. Hardware
Noise Blanker in the Orion I/II and Eagle does the same, a much better job
though. Again, before the DSP does AGC, hence, if HW NB was on, it would
not have loaded up the AGC.
Either one do affect the audio though, and it is really recommended that
unless you need it, don't use it. Some use it because it makes the RX sound
smoother, well, it will, but it may be due to the fact that they are
removing a bit of QRN and in previous builds, the QRN would be enough to
load the AGC and cause some RX level changes, which sounded rougher.
My advice with the Orion and Orion II latest releases and the OMNI-VII beta
1.035h, turn them off and see how well the audio now sounds. Again, it is
subjective, if you do hear the QRN now, you should of course pick the NB of
choice. I vote for HW NB, but, aggressiveness and effect is up to your
ears, and your ears only.
Noise Reduction.
Noise Reduction is meant to adaptively over time adjust reception of
broadcasted signals so that noises that are there all of the time get taken
away. May not be a good description, but, the thing to note.... it is an
iterative process over time, so, unlike NB that just "nails" impulses, NR
will adjust the audio until noise that contributes to non-legibility will
slowly go away. The faster you want it to go away is adjustable. This has a
side effect, making it more aggressive can really ramp up/down the
effectiveness. With the previous builds, when you had the NB's turned off,
and you had QRN, well, the NR routine will process that QRN as well, not a
big deal, but the big deal was the processing of the "AGC loaded up" time
as well. So it's effectiveness in a QRN free environment might be
excellent, but in an environment that has occasional QRN, well, not as
good, and then more periodic QRN, well, it should never be used.
Now, with the latest releases for the Orion and the Orion II, this effect
is removed. SEVERAL comments coming in on how we have made such a great
improvement in the NR. Well, we didn't touch the NR, but we did change the
data going to the NR algorithm... before.... garbage in = garbage out...
Now, it is a bit more effective. Probably needs some more attention itself
down the road, but, time will tell.
Noise Reduction works on data later in the DSP chain than the Noise Blanker
does.
It is also performed after AutoNotch and Manual Notch. The reason is to
clean out tones and stuff you don't want to hear before the NR takes
effect. In the case of FM it is done before deemphasis is applied.
The important thing to remember, it is done after NB, and also after AGC
would have loaded up in previous releases. So, in the latest releases of
the Orion and Orion II, and the beta OMNI-VII 1.035h, it has a cleaner
input to the algorithm than it did before.
Now, granted, there are those that say they never have and never will use
any kind of DSP NR/NB/whatever function to act on data.
Their tools are the bandwidth, PBT, and for the Orion / Orion II they may
use SAF, Hi-Cut, Lo-Cut etc to "filter" the edges and boost the internals
of what they are listening for, and their own mind to pull the audio out
they are listening for.
I myself am a big fan of hardware Noise Blankers BUT, only WHEN NEEDED, and
a lesser fan of Software Noise Blankers (but they do perform, just not as
clean as HW does), and not so much a fan of Noise Reduction UNLESS
absolutely necessary. The OMNI-VII for me cuts out 90% of what I'd ever
want with it's software featuring and roofing filters.
Brought up this stuff above because I think it is a good ground for
discussions of experience amongst the group. Don't need to keep this title,
respond with a title that makes sense for the specific area you want to
comment on... or not... up to you.
Thanks, and 73,
John Henry, KI4JPL
TEN-TEC Engineering
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