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

From: Spencer Graves <spencer.graves_at_pdf.com>
Date: Tue 31 Jan 2006 - 12:45:58 EST

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)
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