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Discrete Fourier Transform (DFT) viewer and/or file format

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  Discrete Fourier Transform (DFT) viewer and/or file format Dan Hitt <dan.hitt@gmail.com> - 2017-11-13 04:50 +0100
    Re: Discrete Fourier Transform (DFT) viewer and/or file format Richard Owlett <rowlett@cloud85.net> - 2017-11-13 06:00 +0100
      Re: Discrete Fourier Transform (DFT) viewer and/or file format Dan Hitt <dan.hitt@gmail.com> - 2017-11-13 07:10 +0100
        Re: Discrete Fourier Transform (DFT) viewer and/or file format Eike Lantzsch <zp6cge@gmx.net> - 2017-11-13 10:00 +0100
          Re: Discrete Fourier Transform (DFT) viewer and/or file format Henning Follmann <hfollmann@itcfollmann.com> - 2017-11-13 15:10 +0100
        Re: Discrete Fourier Transform (DFT) viewer and/or file format Richard Owlett <rowlett@cloud85.net> - 2017-11-13 13:30 +0100
    Re: Discrete Fourier Transform (DFT) viewer and/or file format <tomas@tuxteam.de> - 2017-11-13 10:40 +0100
      Re: Discrete Fourier Transform (DFT) viewer and/or file format Dan Hitt <dan.hitt@gmail.com> - 2017-11-14 06:20 +0100
        Re: Discrete Fourier Transform (DFT) viewer and/or file format tomas@tuxteam.de - 2017-11-14 14:20 +0100
    Re: Discrete Fourier Transform (DFT) viewer and/or file format Henning Follmann <hfollmann@itcfollmann.com> - 2017-11-13 15:20 +0100

#188931 — Discrete Fourier Transform (DFT) viewer and/or file format

I have some DFTs that i wish to inspect.  (Apparently DFT is a common
acronym, but here i mean Discrete Fourier Transform.  And properly
speaking it doesn't make sense to inspect a transform, but only to
inspect transformed data, but i'm speaking colloquially.)

DFTs are a common artifact in digital signal processing.  Lots of
Debian packages are focused on FFTs (Fast Fourier Transforms, a way of
computing DFTs).  Nevertheless i couldn't find either a standard file
format to store one, or software specifically for viewing DFTs.

Of course, lots of software can take data, then transform it, then
display the transform that it created, but i would like something that
can take an already created DFT in some standard format, then display
it.

TIA for any information or pointers or advice from anybody! :)

dan

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#188933

On 11/12/2017 09:45 PM, Dan Hitt wrote:
> I have some DFTs that i wish to inspect.  (Apparently DFT is a common
> acronym, but here i mean Discrete Fourier Transform.  And properly
> speaking it doesn't make sense to inspect a transform, but only to
> inspect transformed data, but i'm speaking colloquially.)
>
> DFTs are a common artifact in digital signal processing.  Lots of
> Debian packages are focused on FFTs (Fast Fourier Transforms, a way of
> computing DFTs).  Nevertheless i couldn't find either a standard file
> format to store one, or software specifically for viewing DFTs.
>
> Of course, lots of software can take data, then transform it, then
> display the transform that it created, but i would like something that
> can take an already created DFT in some standard format, then display
> it.
>
> TIA for any information or pointers or advice from anybody! :)
>
> dan
>
>

A useful set of expertise is available at the USENET group at comp.dsp .
HTH

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#188934

On Sun, Nov 12, 2017 at 8:50 PM, Richard Owlett <rowlett@cloud85.net> wrote:
> On 11/12/2017 09:45 PM, Dan Hitt wrote:
>>
>> I have some DFTs that i wish to inspect.  (Apparently DFT is a common
>> acronym, but here i mean Discrete Fourier Transform.  And properly
>> speaking it doesn't make sense to inspect a transform, but only to
>> inspect transformed data, but i'm speaking colloquially.)
>>
>> DFTs are a common artifact in digital signal processing.  Lots of
>> Debian packages are focused on FFTs (Fast Fourier Transforms, a way of
>> computing DFTs).  Nevertheless i couldn't find either a standard file
>> format to store one, or software specifically for viewing DFTs.
>>
>> Of course, lots of software can take data, then transform it, then
>> display the transform that it created, but i would like something that
>> can take an already created DFT in some standard format, then display
>> it.
>>
>> TIA for any information or pointers or advice from anybody! :)
>>
>> dan
>>
>>
>
> A useful set of expertise is available at the USENET group at comp.dsp .
> HTH

Thanks Richard.

Maybe you're exactly right, because if i can find any free software
that's relevant to what i want, then i can probably get it to Debian.
(If i have something specific, then can bring it up here in fact if i
have trouble installing it.)

How do you normally access usenet?

In the old days (meaning, decades ago) i used to read usenet with rn.

I suppose a modern equivalent would be google groups, but if i do get
back in the usenet scene, i'm wondering if there's a more
command-liney thing or just other alternatives to consider before
walking down the google trail.

Anyhow, whether or not you have an answer about the best way to go to
usenet, i appreciate the suggestion because that group (comp.dsp) is
probably where i can find what i'm looking for if it exists at all.

dan

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#188938

On Sunday, November 12, 2017 10:06:11 PM -03 Dan Hitt wrote:
> On Sun, Nov 12, 2017 at 8:50 PM, Richard Owlett <rowlett@cloud85.net> wrote:
> > On 11/12/2017 09:45 PM, Dan Hitt wrote:
> >> I have some DFTs that i wish to inspect.  (Apparently DFT is a common
> >> acronym, but here i mean Discrete Fourier Transform.  And properly
> >> speaking it doesn't make sense to inspect a transform, but only to
> >> inspect transformed data, but i'm speaking colloquially.)
> >> 
> >> DFTs are a common artifact in digital signal processing.  Lots of
> >> Debian packages are focused on FFTs (Fast Fourier Transforms, a way of
> >> computing DFTs).  Nevertheless i couldn't find either a standard file
> >> format to store one, or software specifically for viewing DFTs.
> >> 
> >> Of course, lots of software can take data, then transform it, then
> >> display the transform that it created, but i would like something that
> >> can take an already created DFT in some standard format, then display
> >> it.
> >> 
> >> TIA for any information or pointers or advice from anybody! :)
> >> 
> >> dan
> > 
> > A useful set of expertise is available at the USENET group at comp.dsp .
> > HTH
> 
> Thanks Richard.
> 
> Maybe you're exactly right, because if i can find any free software
> that's relevant to what i want, then i can probably get it to Debian.
> (If i have something specific, then can bring it up here in fact if i
> have trouble installing it.)
> 
> How do you normally access usenet?
> 
> In the old days (meaning, decades ago) i used to read usenet with rn.
ask for an account on (€10 per year)
http://www.individual.net/
install leafnode and slrn on Debian

[snip]

-- 
Eike Lantzsch ZP6CGE

Hay potentes, impotentes y prepotentes.

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#188947

On Mon, Nov 13, 2017 at 05:49:42AM -0300, Eike Lantzsch wrote:
> On Sunday, November 12, 2017 10:06:11 PM -03 Dan Hitt wrote:
> > On Sun, Nov 12, 2017 at 8:50 PM, Richard Owlett <rowlett@cloud85.net> wrote:
> > > On 11/12/2017 09:45 PM, Dan Hitt wrote:
> > >> I have some DFTs that i wish to inspect.  (Apparently DFT is a common
> > >> acronym, but here i mean Discrete Fourier Transform.  And properly
> > >> speaking it doesn't make sense to inspect a transform, but only to
> > >> inspect transformed data, but i'm speaking colloquially.)
> > >> 
> > >> DFTs are a common artifact in digital signal processing.  Lots of
> > >> Debian packages are focused on FFTs (Fast Fourier Transforms, a way of
> > >> computing DFTs).  Nevertheless i couldn't find either a standard file
> > >> format to store one, or software specifically for viewing DFTs.
> > >> 
> > >> Of course, lots of software can take data, then transform it, then
> > >> display the transform that it created, but i would like something that
> > >> can take an already created DFT in some standard format, then display
> > >> it.
> > >> 
> > >> TIA for any information or pointers or advice from anybody! :)
> > >> 
> > >> dan
> > > 
> > > A useful set of expertise is available at the USENET group at comp.dsp .
> > > HTH
> > 
> > Thanks Richard.
> > 
> > Maybe you're exactly right, because if i can find any free software
> > that's relevant to what i want, then i can probably get it to Debian.
> > (If i have something specific, then can bring it up here in fact if i
> > have trouble installing it.)
> > 
> > How do you normally access usenet?
> > 
> > In the old days (meaning, decades ago) i used to read usenet with rn.
> ask for an account on (€10 per year)
> http://www.individual.net/
> install leafnode and slrn on Debian
> 

aioe.org has free access to usenet (if text only groups suffice).

-H


-- 
Henning Follmann           | hfollmann@itcfollmann.com

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#188944

On 11/13/2017 12:06 AM, Dan Hitt wrote:
> On Sun, Nov 12, 2017 at 8:50 PM, Richard Owlett <rowlett@cloud85.net> wrote:
>> On 11/12/2017 09:45 PM, Dan Hitt wrote:
>>>
>>> I have some DFTs that i wish to inspect.  (Apparently DFT is a common
>>> acronym, but here i mean Discrete Fourier Transform.  And properly
>>> speaking it doesn't make sense to inspect a transform, but only to
>>> inspect transformed data, but i'm speaking colloquially.)
>>>
>>> DFTs are a common artifact in digital signal processing.  Lots of
>>> Debian packages are focused on FFTs (Fast Fourier Transforms, a way of
>>> computing DFTs).  Nevertheless i couldn't find either a standard file
>>> format to store one, or software specifically for viewing DFTs.
>>>
>>> Of course, lots of software can take data, then transform it, then
>>> display the transform that it created, but i would like something that
>>> can take an already created DFT in some standard format, then display
>>> it.
>>>
>>> TIA for any information or pointers or advice from anybody! :)
>>>
>>> dan
>>>
>>>
>>
>> A useful set of expertise is available at the USENET group at comp.dsp .
>> HTH
>
> Thanks Richard.
>
> Maybe you're exactly right, because if i can find any free software
> that's relevant to what i want, then i can probably get it to Debian.
> (If i have something specific, then can bring it up here in fact if i
> have trouble installing it.)

I know there are Ubuntu users on that list as one pointed me in that 
direction when I escaped Windows. That's how I found Debian ;}

>
> How do you normally access usenet?

As a former Netscape user, I find SeaMonkey comfortable 
[http://www.seamonkey-project.org/]

>
> In the old days (meaning, decades ago) i used to read usenet with rn.
>
> I suppose a modern equivalent would be google groups, but if i do get
> back in the usenet scene, i'm wondering if there's a more
> command-liney thing or just other alternatives to consider before
> walking down the google trail.

I avoid Google!
For a free news server I have used http://www.aioe.org/ .
I currently use a paid service, https://www.supernews.com/ .

>
> Anyhow, whether or not you have an answer about the best way to go to
> usenet, i appreciate the suggestion because that group (comp.dsp) is
> probably where i can find what i'm looking for if it exists at all.

The group is composed primarily of those using DSP on a daily basis.

>
> dan
>

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#188941

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On Sun, Nov 12, 2017 at 07:45:13PM -0800, Dan Hitt wrote:
> I have some DFTs that i wish to inspect.  (Apparently DFT is a common
> acronym, but here i mean Discrete Fourier Transform.  And properly
> speaking it doesn't make sense to inspect a transform, but only to
> inspect transformed data, but i'm speaking colloquially.)

Uh, oh. To answer that without getting lost in Hilbert Space means
consulting my (rusty) crystal ball :-)

Now more seriously: what do you mean by "inspecting" a DFT?

A DFT is just a trick to approximate a Fourier transform on an
(approximate) function. Are you talking about one dimensional
functions (e.g. a function of time) or two (three, etc.) dimensional
functions? Their transforms are, correspondingly, one, two (and
so on) dimensional functions, so the visualization techniques
vary, depending on dimensionality and on the conventions current
in the field (engineering, social sciences, maths, whatever).

I'd recommend looking into some of the many (excellent) scientific
packages having a visualization components, each one of which
has a teeming community willing to help you.

For three examples off the top of my head (all three packaged
in Debian):

  GNU Octave   https://www.gnu.org/software/octave/
  NumPy        http://www.numpy.org/
  GNU R        https://www.r-project.org/

The last one is touted as "statistical package", but let me tell
you: all three are not only capable of visualizing (the result of)
a discrete DFT, but all three can calculate one for you :-)

Now if you are trying to visualize the result of a DFT on an image
(a special two dimensional case, where you think of the discrete
elements as of pixels), then perhaps a graphical package (e.g.
The Gimp) is your friend. Also packaged in Debian.

For more of those "scientific computing" packages, browsing this

  https://wiki.debian.org/DebianScience

might be of interest (or just drop "Debian scientific computing"
into your favourite search engine, which hopefully ain't Google).

Enjoy

- -- tomás
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#188972

On Mon, Nov 13, 2017 at 1:31 AM,  <tomas@tuxteam.de> wrote:
> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> On Sun, Nov 12, 2017 at 07:45:13PM -0800, Dan Hitt wrote:
>> I have some DFTs that i wish to inspect.  (Apparently DFT is a common
>> acronym, but here i mean Discrete Fourier Transform.  And properly
>> speaking it doesn't make sense to inspect a transform, but only to
>> inspect transformed data, but i'm speaking colloquially.)
>
> Uh, oh. To answer that without getting lost in Hilbert Space means
> consulting my (rusty) crystal ball :-)
>
> Now more seriously: what do you mean by "inspecting" a DFT?
>
> A DFT is just a trick to approximate a Fourier transform on an
> (approximate) function. Are you talking about one dimensional
> functions (e.g. a function of time) or two (three, etc.) dimensional
> functions? Their transforms are, correspondingly, one, two (and
> so on) dimensional functions, so the visualization techniques
> vary, depending on dimensionality and on the conventions current
> in the field (engineering, social sciences, maths, whatever).
>
> I'd recommend looking into some of the many (excellent) scientific
> packages having a visualization components, each one of which
> has a teeming community willing to help you.
>
> For three examples off the top of my head (all three packaged
> in Debian):
>
>   GNU Octave   https://www.gnu.org/software/octave/
>   NumPy        http://www.numpy.org/
>   GNU R        https://www.r-project.org/
>
> The last one is touted as "statistical package", but let me tell
> you: all three are not only capable of visualizing (the result of)
> a discrete DFT, but all three can calculate one for you :-)
>
> Now if you are trying to visualize the result of a DFT on an image
> (a special two dimensional case, where you think of the discrete
> elements as of pixels), then perhaps a graphical package (e.g.
> The Gimp) is your friend. Also packaged in Debian.
>
> For more of those "scientific computing" packages, browsing this
>
>   https://wiki.debian.org/DebianScience
>
> might be of interest (or just drop "Debian scientific computing"
> into your favourite search engine, which hopefully ain't Google).
>
> Enjoy
>

Thanks Tomás, Richard, Eike, and Henning for your replies! :)

As for usenet, thanks for the leads on the various providers
(aeiou.net, individual.net, supernews.com).  I'm still pondering what
to do about that, but text-only groups are a plus imvho.

Tomás, you are right to question me about the dimension.  How could i
expect anybody to read my mind?

Now, although i'm curious about how multidimensional DFTs might be
stored, what i secretly had in mind was the 1d case.

And although under suitable conditions a DFT can approximate a Fourier
transform or series, i'd be content with just the case of inspecting
the transform of finitely many points without any reference to
limiting behavior.  (More about 'inspecting' below.)

And it is true that it has never been easier to take a DFT, at least a
1d one with packages like FFTW (which presumably is compiled into
numpy and octave, and maybe R?).

The actual problem i faced was that i had a long computation and deep
in the middle somewhere was a DFT, and my results made no sense.
Subsequently it turned out that i goofed on a factor of 2, so my
question is moot now, at least, until i get stuck the same way again.

But before i knew where my mistake was, i thought surely i could emit
the DFT from the midst of the computation and do a sanity check on it.

And i didn't want to reinvent any wheels.

So since so many people deal with DFTs for doing so many things, it
seemed like there might be a standard format lying around somewhere
that i could just use.

Sort of like if you have an image you'd like to see, you can convert
it to jpg or png or some other widely known format, and take a look at
it.  The 'file' program knows exactly what such an image format is,
and there's a universal, unambiguous interpretation.

So i was hoping there was a DFT format of some sort, that would be
recognized by the standard tools, and i could just put the data in the
standard format, and use some standard tool let me inspect it -----
i.e., represent the magnitude and phase somehow, maybe provide some
clues as to where most of the mass was, that sort of thing.  I
wouldn't want to code my own tool for doing it, because i was already
doing it wrong (despite how easy and reliable our modern software
development is).  I wanted to use somebody else's tool as a check
against me repeatedly making the same error of whatever sort.

However, my guess is that Henning is right, and this just doesn't
exist, but if it does exist, i'd like to know about it ! :) :)

And . . . thanks for the reference to DebianScience.

Thanks everybody for all your help!

dan

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#188976

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On Mon, Nov 13, 2017 at 09:15:39PM -0800, Dan Hitt wrote:

[...]

> Thanks Tomás, Richard, Eike, and Henning for your replies! :)

Glad to help :)

> As for usenet, thanks for the leads on the various providers
> (aeiou.net, individual.net, supernews.com).  I'm still pondering what
> to do about that, but text-only groups are a plus imvho.

There's also eternal september <https://www.eternal-september.org/>.

Happy user here.

> Tomás, you are right to question me about the dimension.  How could i
> expect anybody to read my mind?

[...]

Well, all of us try, a bit. It's the essence of communication. But
I disgress...

Glad you found the bug.

Cheers
- -- tomás
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#188948

On Sun, Nov 12, 2017 at 07:45:13PM -0800, Dan Hitt wrote:
> I have some DFTs that i wish to inspect.  (Apparently DFT is a common
> acronym, but here i mean Discrete Fourier Transform.  And properly
> speaking it doesn't make sense to inspect a transform, but only to
> inspect transformed data, but i'm speaking colloquially.)
> 
> DFTs are a common artifact in digital signal processing.  Lots of
> Debian packages are focused on FFTs (Fast Fourier Transforms, a way of
> computing DFTs).  Nevertheless i couldn't find either a standard file
> format to store one, or software specifically for viewing DFTs.
> 
> Of course, lots of software can take data, then transform it, then
> display the transform that it created, but i would like something that
> can take an already created DFT in some standard format, then display
> it.
> 
> TIA for any information or pointers or advice from anybody! :)
> 
> dan
> 

First things first: there is no special format for FT data.
Since mostly you deal with time series/sequential data any format should work.


To display that data any plotting program will do. 
gnuplot,
mathplot...

If you look for a easy integration into your transformation routines, I
suggest numpy/scipy which uses mathplot.

-H

-- 
Henning Follmann           | hfollmann@itcfollmann.com

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