Gary,
you sure the dsp BW filtering is audio? Seems to me that it is in the 3rd if
at 14KhZ? Is my thinking wrong? Now if you are talking about NR then I agree
with you.
And I agree with your expected DSP explanation...this is what I am
accustomed to.
On 5/3/06, Gary Hoffman <ghoffman@spacetech.com> wrote:
FWIW.....not ALL DSP just narrows bandwidth.
The way it worked when I used to work with audio DSP systems in a previous
life (and the IF of the Orion is at an audio frequency) is that each
sample
of the A to D converter is compared to those around it, and a correlation
level is established. (Excuse me that I've forgotten the correct
technical
language they used). Speech and tones (like CW) are highly correlated, in
that each sample tends to be relatively closely related to those that came
before. Random noise, of course, is not highly correlated.
The noise is reduced by simply deleting those samples not correlated.
Then the remainder go through D to A and come out as sound again.
The NR reduction level control (or whatever its called) simply shifts how
much correlation is required before a sample is either kept or
rejected. A
higher setting requires more correlation before the sample is kept. Of
course if you turn it up too high, then too many samples are rejected, and
you get weird sounding sound after you go back from Digital to Audio.
Has nothing whatsoever to do with a bandwidth limiting filter. That, of
course, is another approach, which works to a certain degree also. But
not
what a real DSP noise reducer does.
Now....how much of each does the Orion do ? That I cannot tell you, not
being privvy to the design details. Perhaps the folks at Ten Tec would
like
to tell us ?
Note - years ago, when I did this, we could do it on the fly with a DSP
processor. I'm sure the processors they have now far outperform the ones
we
had then. So, its doable, and practical, essentially with a single chip.
73 de Gary, AA2IZ
----- Original Message -----
From: "Bill Tippett" <btippett@alum.mit.edu>
To: <tentec@contesting.com>
Sent: Wednesday, May 03, 2006 7:05 AM
Subject: Re: [TenTec] 2.033
> NQ5T:
>
> >the one thing I'm absolutely certain of is that it
> adds nothing to (S+N)/N ratio, and at any BW below
> about 1000 Hz actually degrades it.
>
> Just to clarify Orion's implementation
> of DSP NR, I believe your statement is true for ANY
> DSP rig with real-time processing (i.e the DSP is
> achieving NR simply by BW reduction). To do more
> (e.g. JPL's image enhancements) requires reprocessing
> the recorded signal many times with literally hours of
> latency even using super-computers.
>
> There is no free lunch and DSP is not magic,
> despite what some manufacturers (notably not Ten-Tec)
> would lead you to believe.
>
> 73, Bill W4ZV
>
> _______________________________________________
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> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
>
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