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From: Ibraheem Ali on 23 Jun 2010 12:49
Dear All,

I have FFT plot (Freq. vs. Amp.).

Can I produce same plot but as (Period vs. amplitude). Period is (1/freq.)?

The problem is the plot does not accept values that is in ascending order (high to low) values.

your help is greatly appreciated

Thank you

IA
From: Greg Heath on 23 Jun 2010 14:11
On Jun 23, 12:49 pm, "Ibraheem Ali" <ialhak...(a)hotmail.com> wrote:
> Dear All,
>
> I have FFT plot (Freq. vs. Amp.).

I think you mean Amp vs Freq

> Can  I produce same plot but as (Period vs. amplitude). Period is (1/freq.)?

Except for the zero frequency component.

However, why in the world would you want to do it in the
first place? All of the frequencies are harmonics of the
fundamental are evenly spaced. The spacing of 1/freq
would result in strange looking plots that could only
mean something to you personally.

If you don't like linear/linear plots try log/linear, log/log
or even linear/log. Anything else keep hidden in your
desk or file cabinet.

Hope this deters you,

Greg
From: TideMan on 23 Jun 2010 16:26
On Jun 24, 6:11 am, Greg Heath <he...(a)alumni.brown.edu> wrote:
> On Jun 23, 12:49 pm, "Ibraheem Ali" <ialhak...(a)hotmail.com> wrote:
>
> > Dear All,
>
> > I have FFT plot (Freq. vs. Amp.).
>
> I think you mean Amp vs Freq
>
> > Can  I produce same plot but as (Period vs. amplitude). Period is (1/freq.)?
>
> Except for the zero frequency component.
>
> However, why in the world would you want to do it in the
> first place? All of the frequencies are harmonics of the
> fundamental are evenly spaced. The spacing of 1/freq
> would result in strange looking plots that could only
> mean something to you personally.
>
> If you don't like linear/linear plots try log/linear, log/log
> or even linear/log. Anything else keep hidden in your
> desk or file cabinet.
>
> Hope this deters you,
>
> Greg

Greg:
It depends on the end-user.
For mariners, they are used to wave spectra in seconds, not Hz, so we
plot it that way, as shown here in the bottom plot on this page:
http://www.mulgor.co.nz/MarsPt/TriaxysWaveBuoy.html

But note that the axis is reversed:
set(gca,...
'XDir','reverse')
and the spectrum is plotted log-log.
From: Greg Heath on 23 Jun 2010 19:37
On Jun 23, 4:26 pm, TideMan <mul...(a)gmail.com> wrote:
> On Jun 24, 6:11 am, Greg Heath <he...(a)alumni.brown.edu> wrote:
>
>
>
>
>
> > On Jun 23, 12:49 pm, "Ibraheem Ali" <ialhak...(a)hotmail.com> wrote:
>
> > > Dear All,
>
> > > I have FFT plot (Freq. vs. Amp.).
>
> > I think you mean Amp vs Freq
>
> > > Can  I produce same plot but as (Period vs. amplitude). Period is (1/freq.)?
>
> > Except for the zero frequency component.
>
> > However, why in the world would you want to do it in the
> > first place? All of the frequencies are harmonics of the
> > fundamental are evenly spaced. The spacing of 1/freq
> > would result in strange looking plots that could only
> > mean something to you personally.
>
> > If you don't like linear/linear plots try log/linear, log/log
> > or even linear/log. Anything else keep hidden in your
> > desk or file cabinet.
>
> > Hope this deters you,
>
> > Greg
>
> Greg:
> It depends on the end-user.
> For mariners, they are used to wave spectra in seconds, not Hz, so we
> plot it that way, as shown here in the bottom plot on this page:http://www.mulgor.co.nz/MarsPt/TriaxysWaveBuoy.html
>
> But note that the axis is reversed:
> set(gca,...
> 'XDir','reverse')
> and the spectrum is plotted log-log.- Hide quoted text -
>
> - Show quoted text -

Well, in that case, if IA doesn't mind, I'll retrieve my sarcasm
in the reply to him and save it for a reply to someone else.

Sorry IA.

Greg

From: Ibraheem Ali on 24 Jun 2010 02:20
"Ibraheem Ali" <ialhakeem(a)hotmail.com> wrote in message <hvtdu0$jki$1(a)fred.mathworks.com>...
> Dear All,
>
> I have FFT plot (Freq. vs. Amp.).
>
> Can I produce same plot but as (Period vs. amplitude). Period is (1/freq.)?
>
> The problem is the plot does not accept values that is in ascending order (high to low) values.
>
> your help is greatly appreciated
>
> Thank you
>
> IA

Thank you very much for all the comments,

actually I use this in some geophysical data which I need to present the period of the phenomena. Thanks again
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