<p>In the cited paper their methodology is explained in the Materials and Methods section on  p.209, where it says:</p>

<blockquote>
  <p>Fig. 4 shows the norm of the CoP during the experiment [...] which are represented by spikes in the norm of the CoP [...] In order to characterize the movement properties of the CoP, we have computed the corresponding spectra over the experiment stages [...]. Fig. 5 shows the spectra of the norm of the CoP [...].</p>
</blockquote>

<p>Spectra, or more appropriately called <strong>frequency spectra</strong> or spectrograms, are typically generated by <strong>Fast Fourier Transformation</strong> (FFT). FFT essentially decomposes a signal into a collection of sine waves. The <strong>x-axis</strong> of a spectrogram (like Fig. 5 in the article) represents the <strong>frequency</strong> of each sine wave, the <strong>y-axis</strong> the magnitude (amplitude or more aptly the '<strong>power</strong>') of each sine wave in the frequency spectrum.</p>

CC BY-SA 3.0
2014-12-30T11:01:50.907Z
2015-01-24T21:55:34.450Z
2015-01-24T21:55:34.450Z
AliceD
<p>Recently, I studied a paper called "What Does Your Chair Know About Your Stress Level?</p>

<p>It can be download at the link below.</p>

<blockquote>
  <p><a href="http://www.barnrich.ch/wiki/data/media/pub/2010_what_does_your_chair_know_about_your_stress_level.pdf" rel="nofollow noreferrer">http://www.barnrich.ch/wiki/data/media/pub/2010_what_does_your_chair_know_about_your_stress_level.pdf</a></p>
</blockquote>

<p>at page 210, Fig.5 (picture 5) mentioned that</p>

<blockquote>
  <p>Spectra of the norm of the CoP vector during the experiment (stages 3–7) for the same subject used in Fig. 4.</p>
</blockquote>

<p>How did they do to transform Fig.4 to Fig.5? And what do x-axis and y-axis mean in Fig.5?</p>

<p>Fig4
<img src="https://i.sstatic.net/Iq7qc.png" alt="Fig4"></p>

<p>Fig5
<img src="https://i.sstatic.net/7HPxu.png" alt="Fig5"></p>

<experimental-psychology><task-analysis>
How to transform data to a frequency spectrum?
JackSie
# How to transform data to a frequency spectrum?

(Asked by: username_0 on 2014-12-30)

Recently, I studied a paper called "What Does Your Chair Know About Your Stress Level?

It can be download at the link below.

> <http://www.barnrich.ch/wiki/data/media/pub/2010_what_does_your_chair_know_about_your_stress_level.pdf>

at page 210, Fig.5 (picture 5) mentioned that

> Spectra of the norm of the CoP vector during the experiment (stages 3–7) for the same subject used in Fig. 4.

How did they do to transform Fig.4 to Fig.5? And what do x-axis and y-axis mean in Fig.5?

Fig4
![Fig4](https://i.sstatic.net/Iq7qc.png)

Fig5
![Fig5](https://i.sstatic.net/7HPxu.png)

**Tags:** experimental-psychology, task-analysis


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## 1 answers

### Answer by username_1 on 2014-12-30. Score: 6 | Accepted answer

In the cited paper their methodology is explained in the Materials and Methods section on p.209, where it says:

> Fig. 4 shows the norm of the CoP during the experiment [...] which are represented by spikes in the norm of the CoP [...] In order to characterize the movement properties of the CoP, we have computed the corresponding spectra over the experiment stages [...]. Fig. 5 shows the spectra of the norm of the CoP [...].

Spectra, or more appropriately called **frequency spectra** or spectrograms, are typically generated by **Fast Fourier Transformation** (FFT). FFT essentially decomposes a signal into a collection of sine waves. The **x-axis** of a spectrogram (like Fig. 5 in the article) represents the **frequency** of each sine wave, the **y-axis** the magnitude (amplitude or more aptly the '**power**') of each sine wave in the frequency spectrum.


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