Power Spectral Density - how can I get a link back to the original signal

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Discussion Overview

The discussion centers on analyzing a biological signal for periodicities using Fourier transforms, specifically focusing on obtaining a frequency distribution plot and marking the positions of certain frequencies that correspond to peaks in the plot.

Discussion Character

  • Exploratory, Technical explanation, Homework-related

Main Points Raised

  • One participant inquires about methods to analyze a biological signal using Fourier transforms to identify periodicities and frequency distributions.
  • Another participant suggests that performing a Fast Fourier Transform (FFT) on the entire signal is not suitable, as each point in the FFT spectrum is influenced by all points in the time domain signal.
  • A suggestion is made to use a "windowed" FFT approach, where the signal is divided into segments for analysis, or to apply a moving window to observe how the spectrum changes over time.
  • A participant acknowledges the idea of using a moving window but expresses uncertainty about its implementation, indicating a potential need to write the code in Matlab.
  • Another participant mentions that the Matlab signal processing toolbox contains necessary functions and provides a reference to the short-time Fourier transform as a relevant concept.

Areas of Agreement / Disagreement

Participants do not reach a consensus on a single method for analysis, as multiple approaches are suggested, and uncertainty remains regarding the implementation of the moving window technique.

Contextual Notes

There are limitations regarding the assumptions made about the signal characteristics and the specific requirements for the analysis, which are not fully detailed in the discussion.

Who May Find This Useful

This discussion may be useful for individuals interested in signal processing, particularly in the context of biological signals and Fourier analysis techniques.

Dr Ingend
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Hi everyone!

I would like to analyze a biological signal for periodicities using a Fourier transform, i.e., I'd like to get a frequency distribution plot based on a long stretch of signal. Additionally, I would like to be able to mark the positions of certain frequencies within the signal that give rise to a peak in the freq distribut plot.

Do you have any suggestions how to perform such an analysis?

Thanks in advance!
 
Last edited:
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If you did FFT of the whole signal, you cannot do this.
Each point of the FFT spectrum depends on all the points of the time domain signal.
You can do the so call "windowed" FFT when you cut your signal in several segments and do FFT transform for each. Or you use a mowing window and see how the spectrum evolves as you move the window.
 
Thank you! I thought about a moving window as well, but wasn't sure how to actually make it work. I think I would have to write it in Matlab from scratch.

Cheers
 

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