[opendtv] Re: Integrated DTV PSIP
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Tue, 6 Dec 2005 15:31:50 -0500
Cliff Benham wrote:
> After 40 plus years in broadcast engineering I can
> assure you it is impossible to judge the performance of
> *anything* by it's spec sheet or sales brochure.
Hmmm.
Since all I have done is quote directly out of CRC test
results, and you quoted my post, am I to conclude that
the Communications Research Centre of Canada in fact
only writes sales brochures?
> Direct comparison under identical test conditions is the
> *only* way to know which device works best.
Not wanting to sound overly pedantic here, but ...
When an engineer designs something, he has to use both
measurements and real-world tests. The measurements are
needed to associate behavior in the real world with
specific aspects of the design. It is only with these
measurements, and associated real-world tests, that an
engineer can go back and tweak the design in a attempt
to affect real-world behavior. Otherwise, he's just
shooting in the dark.
The example of the comparative results of the newer
receivers in Mark Schubin's apartment are a good case in
point. The one which was most successful was one that did
not measure best in equalizer performance, with respect
to both static or dynamic echo. This leads to the
conclusion, at least in *that* site, that equalizer
performance was adequate "as is" with the LG, and that it
must have been other aspects of the design which made it
particularly successful.
This conclusion was further supported by the results with
the LG clones, which used the same equalizer as the LG
prototype and yet got results more similar to those of
the other, less successful contestants. Good, not great.
Furthermore:
The LG did not test as well as A/74 guidelines. Therefore,
one can conclude that A/74 guidelines with respect to
echo tolerance *per se* are probably more than adequate,
but that A/74 guidelines *may* not adequately address other
aspects of receiver design. And that these other aspects
have an important impact on real world performance.
This was the gist of the post you quoted. Sales brochures
have never been the issue in any of this, at least not
from my posts.
Bert
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