On 2/3/2013 4:13 PM, Rick - DJ0IP / NJ0IP wrote:
So on a given day, you might
clearly see that a radio with a 3kHz roofing filter
sounds better than ...
You some good points, and this particular comment
raises a different, but closely related, aspect of
comparison testing - namely the very subjective
determination of which radio "sounds better."
Bottom Line Question --
CAN WE REALLY DETERMINE WHICH IS THE BEST
RADIO IN A SIMPLE A-B TEST? Can we really
account for ALL the salient factors which can
affect our decision?
My half-baked notion:
Determining what radio sound best is, at best,
a very subjective matter, turning on many
aspects and factors along the RF and audio
chain. For example, few hams agree on what
sounds "best" - witness the endless hullabaloo
over external speakers. Witness the debate over
the value of DSP filtering vs audio quality.
People, in general, favor "single-factor" analysis,
constantly advocating what is the single "reason"
for whatever they are trying to explain. But I
believe in multiple causation - that much of what
we observe can only be explained by considering
a multitude of causative factors. Focusing on
roofing filters, without considering the "rest of
the story" seems a bit limiting.
Although I am a mere novice concerning radio
design engineering, I presume a 3 kHz filter may
"sound" different from a 1.8 kHz filter in the same
relative point along the signal chain. Moreover,
it seems logical, if not correct, it will make a
material difference exactly where and how you
implement those filters. Merely altering the
audio EQ frequency curve can have a substantial
effect on what we hear - effectively acting as a
high or low cut filter, eliminating some noise and
signal data the RF filtering passed through.
Each radio will be different in these respects,
affecting any A-B testing we might perform.
But wait, ... there is more! I suppose different
audio components, different RF and audio circuit
designs, different audio EQ, different low cut
and high cut filters, different pass band
filters, the different "skirts" on all filters in
question, the differences in the presence and
amount of digital artifact in very different
DSP schemes, and a host of differences all
have a determining impact on what we hear.
I don't expect any two same-make and model
radios will sound exactly the same.
To me the acid test is the most subjective:
Is the other ham easier to understand
on one radio versus another? On which
rig is he more INTELLIGIBLE.
Overall intelligibility is a function of ALL the
circuits, and ALL the filers in the rig... not just
one filter considered in isolation. I wonder if
focusing on front end roofing filter schemes
will tell us enough to determine which is the
better radio. I just want to be able to hear
and understand the guy... will all of this make
him more intelligible on one rig compared to
another - TO ME, across the desk, not to one
or another RF stage in the rig - does it make
it easier to capture and understand his signal?
In a recent thread, a qualified and experienced
operator disparaged Omni VII audio quality. He
was sincere and technically well informed, and
I respect his opinion. In contrast, however, I
LOVE the audio on my Omni VII - for largely the
same reasons he disparaged it ! TO MY EARS,
signals are more INTELLIGIBLE on it, than on
many other radios.
This whole issue of "sounding good" is related
to the debate over DSP artifact and overall audio
quality. The ideal is for DSP to remove noise,
without adversely affecting audio quality. But
that is merely an ideal, which does not occur in
real life, so, ultimately, the debate turns on
whether or not one can accept the inherent
digital artifact and distortion, or not. There is
no free lunch, especially when it come to
digital artifact and DSP filtering... but, for me,
the acid test is, again, whether or not the filter
makes the other guy more intelligible and easier
to understand. Sometimes it is a handy tool
for doing just that... while other times, it
makes it more difficult to understand the bloke.
Another case of having a too much of a good
thing. I can accept the trade off - at times -
while other guys find the artifact and distortion
anathema, and cry foul at any level. And we
are all entitled to our opinion - having paid
our "dues" through the price of the rig.
For me, the best sounding radio is the one that
makes the other ham easier to understand - after
all I figure we are doing "communications grade"
radio, with the emphasis is on communicating
a message clearly, not on how good we sound
doing it.
Therefore, I am a tad skeptical about any proposed
A-B comparison test where all these OTHER factors
are not fully considered, as I doubt few of us are in
a position to perform any test where they are
fully cancelled or neutralized.
How do we cancel all these OTHER factors
out when making any A-B comparison ???
Considering the front-end roofing filter seems
a tad narrow for my taste - whereas one rig may
pass more desired signal through the roofing filter,
it may end up clipping it later in the RF and audio
chain, so the result may be worse than another
rig that passes less through he front filter, but
does a better job processing and preserving the
signal down the line. Only what reaches my
ears matters to me...
(I say all this more as a question, than as statement
of fact. I still need to learn a lot... so I don my
Teflon suit and await my fate...)
;-)
I will repeat what I said earlier: what we witnessed was a pretty
meaningless test, because we have no knowledge of how each radio was set up.
RF Gain? Attenuator? AGC? Bandwidth? Passband tuning? Maybe it was
legitimate and fair, maybe not. We have no way of knowing because the guy
never said squat about the setup.
I agree. My TS-590s is supposed to have
better receiver specifications than my Omni VII,
but I can easily set either rig up to beat the
other one in a side-by side A-B test scenario -
whether using different RF settings or different
audio settings, all using the same antenna,
speaker, etc. And neither will perform its
best using the respective default settings, so
you cannot just set them to factory default
settings and think the comparison is honest
or fair. (Although I like the Omni VII default
settings better than I like the TS-590s default
settings...)
Sidebar... Both are good radios... but just for
the record, I think it is easier to dial in a weak
signal, and hear what he is saying with the
Omni VII - the wider, smoother, more variable
range of the RF-GAIN control is the most
salient difference. I can get the same result
on both rigs, but getting there is quicker and
easier on the Omni VII.)
Remember...
You can only fool yourself... and I highly
recommend it ! ;-)
Just MY take... I still gotta lot to learn!
____________________ K8JHR ______________
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