# [R] How do I "normalise" a power spectral density analysis?

Spencer Graves spencer.graves at pdf.com
Tue Jan 31 02:45:58 CET 2006

```	  Since I have not seen a reply to this post, I will offer a comment,
even though I have not used spectral analysis myself and therefore have
you intuition about it.  First, from the definitions I read in the
results from, e.g., RSiteSearch("time series power spectral density")
[e.g.,
http://finzi.psych.upenn.edu/R/library/GeneTS/html/periodogram.html] and
"spectral analysis" in Venables and Ripley (2002) Modern Applied
Statistics with S (Springer), I see no reason why you couldn't plot the
spectrum vs. the period rather than the frequency.  Someone else may
help us understand why it is usually plotted vs. the frequency;  I'd
guess that the standard plot looks more like the integrand in the
standard Fourier inversion formula, but I'm not sure.

If you'd like more help from this listserve, you might briefly
describe the problem you are trying to solve, why you think spectral
analysis analysis should help, and include a toy example with some
self-contained R code to illustrate what you tried and what you don't
understand about it.  (And PLEASE do read the posting guide!
"www.R-project.org/posting-guide.html".  Nothing is certain but
following that posting guide will, I believe, tend to increase the speed
and utility of response.)

hope this helps.
spencer graves

Tom C Cameron wrote:

> Hi everyone
>
> Can anyone tell me how I normalise a power spectral density (PSD) plot of a
> periodical time-series. At present I get the graphical output of spectrum VS
> frequency.
>
> What I want to acheive is period VS spectrum? Are these the same things but the
> x-axis scale needs transformed ?
>
> Any help would be greatly appreciated
>
> Tom
> ...........................................................................
> Dr Tom C Cameron                        office: 0113 34 32837 (10.23 Miall)
> Ecology & Evolution Res. Group.         lab: 0113 34 32884 (10.20 Miall)
> School of Biological Sciences           Mobile: 07966160266
> University of Leeds                     email: t.c.cameron at leeds.ac.uk
> Leeds LS2 9JT
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>
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```