Jerry Avins <jya@ieee.org> writes:

> robert bristow-johnson wrote:
>>   ...                                one day, i embarassed myself in
>> the front of a class calling them "holes".  can't imagine what Freudian
>> recesses that came from!
>
> "Poles and holes" has a nice ring to it.

Brings a new meaning to "shut your hole."
-- 
%  Randy Yates                  % "With time with what you've learned, 
%% Fuquay-Varina, NC            %  they'll kiss the ground you walk 
%%% 919-577-9882                %  upon."
%%%% <yates@ieee.org>           % '21st Century Man', *Time*, ELO
http://home.earthlink.net/~yatescr

Jerry Avins wrote:
> Jerry Avins wrote:
> > robert bristow-johnson wrote:
> >>   ...                                one day, i embarassed myself in
> >> the front of a class calling them "holes".  can't imagine what Freudian
> >> recesses that came from!
> >
> > "Poles and holes" has a nice ring to it.
>
> Maybe not. King FM in Seattle streams on MSN Radio - classical
>
> Announced by Ms. Ji Ji Yons (sp) following a certain Saint Saens
> Symphony with a gorgeous final movement:
>
> "A symphony with an organ inserted at just the right place."

i can identify with her.

r b-j

Jerry Avins wrote:
> robert bristow-johnson wrote:
> >   ...                                one day, i embarassed myself in
> > the front of a class calling them "holes".  can't imagine what Freudian
> > recesses that came from!
>
> "Poles and holes" has a nice ring to it.

i think that Larry Flint was making a picture book of that title.

r b-j

Jerry Avins wrote:
> robert bristow-johnson wrote:
>>   ...                                one day, i embarassed myself in
>> the front of a class calling them "holes".  can't imagine what Freudian
>> recesses that came from!
> 
> "Poles and holes" has a nice ring to it.

Maybe not. King FM in Seattle streams on MSN Radio - classical

Announced by Ms. Ji Ji Yons (sp) following a certain Saint Saens 
Symphony with a gorgeous final movement:

"A symphony with an organ inserted at just the right place."

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

robert bristow-johnson wrote:
>   ...                                one day, i embarassed myself in
> the front of a class calling them "holes".  can't imagine what Freudian
> recesses that came from!

"Poles and holes" has a nice ring to it.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

robert bristow-johnson skrev:
> Rune Allnor wrote:
> >
> > Sorry. "Null" means zero in Norwegian. I guess I mixed in some
> > C NULL pointer terminology here...
>
> it usually means "zero" here, too.  sometimes it means "nothing" ("null
> and void" w.r.t. a contract) or similar.  sometimes it means a dip or
> low point (35 years ago, when i was WB0CCA, when tuning the coupling
> capicitor in an antenna coupling circuit, we adjusted to get a "null"
> in the SWR meter - it wasn't always zero but it would be nice if the
> SWR *was* zero).
>
> but i hadn't seen, in any English language textbook about LTI system
> theory, Laplace or Z transforms, etc. those things that were the
> opposite of "poles" called "nulls".

My mastering of the English language is even worse than
my Norwegian...

> one day, i embarassed myself in
> the front of a class calling them "holes".  can't imagine what Freudian
> recesses that came from!

Ouch! "Pole" is very close to the Norwegian "p=E5le", meaning "mast"
or "stick", with the obvious interpretation... better leave it there or

discussing DSP in public will become a criminal offense very soon.

Rune

Rune Allnor wrote:
>
> Sorry. "Null" means zero in Norwegian. I guess I mixed in some
> C NULL pointer terminology here...

it usually means "zero" here, too.  sometimes it means "nothing" ("null
and void" w.r.t. a contract) or similar.  sometimes it means a dip or
low point (35 years ago, when i was WB0CCA, when tuning the coupling
capicitor in an antenna coupling circuit, we adjusted to get a "null"
in the SWR meter - it wasn't always zero but it would be nice if the
SWR *was* zero).

but i hadn't seen, in any English language textbook about LTI system
theory, Laplace or Z transforms, etc. those things that were the
opposite of "poles" called "nulls".  one day, i embarassed myself in
the front of a class calling them "holes".  can't imagine what Freudian
recesses that came from!

r b-j

robert bristow-johnson skrev:
> Rune Allnor wrote:
> > Anton skrev:
> ...
> > > I don't really understand, I thought
> > > if X(w) and Y(w) are fourier transforms for input and output and
> > > H(w) the transfer function of the system.
> > >
> > > H(w) = Y(w) / X(w)
> > >
> > > So couldn't you now just take 1/H(w) as inverse transfer function?
> >
> > No. And you already understand why:
> >
> > > Of course all of that works just for LTI systems, and
> > > you can not reconstruct data where H(w)=0.
> >
> > This is the one, single, tiny detail that throws a spanner in
> > the works: Your approach only works if H(w) has all its nulls
> > well inside the unit circle. Not poles. Nulls.
>
> what we call "zeros" on this side of the pond.
>
> (i had to read this twice to figger out what you meant, Rune.)

Sorry. "Null" means zero in Norwegian. I guess I mixed in some
C NULL pointer terminology here...

Rune

Rune Allnor wrote:
> Anton skrev:
...
> > I don't really understand, I thought
> > if X(w) and Y(w) are fourier transforms for input and output and
> > H(w) the transfer function of the system.
> >
> > H(w) = Y(w) / X(w)
> >
> > So couldn't you now just take 1/H(w) as inverse transfer function?
>
> No. And you already understand why:
>
> > Of course all of that works just for LTI systems, and
> > you can not reconstruct data where H(w)=0.
>
> This is the one, single, tiny detail that throws a spanner in
> the works: Your approach only works if H(w) has all its nulls
> well inside the unit circle. Not poles. Nulls.

what we call "zeros" on this side of the pond.

(i had to read this twice to figger out what you meant, Rune.)

r b-j

Anton wrote:


> I don't really understand, I thought
> if X(w) and Y(w) are fourier transforms for input and output and
> H(w) the transfer function of the system.
> 
> H(w) = Y(w) / X(w)
> 
> So couldn't you now just take 1/H(w) as inverse transfer function?
> Of course all of that works just for LTI systems, and
> you can not reconstruct data where H(w)=0.

Nor can you reasonably reconstruct quantized and possibly noisy data 
when H(w) is small. "Small" can be distressingly large.

> But what other methods are used?

In the online book at http://www.dspguide.com/, pages 179 and 180 
(Chapter 9) lay out the basic idea (which you evidently understand) and 
pages 300 to 305 (Chapter 17) have more discussion and some examples. 
almost always, compromises need to be made, and they depend on the 
original data and the final use.

Pages 407 to 410 (Chapter 24) describe deconvolution of if the 
illumination in an image to flatten brightness and contrast. Just about 
every application is a special case.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������