Power spectrum of short signals

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Discussion Overview

The discussion revolves around calculating the power spectrum of short signals, specifically those with durations between 200 and 500 ms. Participants explore the challenges and potential methods for accurately analyzing these short segments, considering both theoretical and practical aspects.

Discussion Character

  • Exploratory, Technical explanation, Debate/contested

Main Points Raised

  • One participant inquires about methods to calculate the power spectrum for short signals, expressing concerns about the accuracy of standard techniques.
  • Another participant suggests using Matlab's FFT to compute the power spectrum, indicating that it is effective for longer segments but may not perform well for shorter ones.
  • A follow-up response acknowledges the use of FFT in Matlab but emphasizes the need for improved algorithms tailored for short segments, as FFT yields poor results for durations under 500 ms.
  • Another participant argues that the critical factor is not the absolute length of the segment but its length relative to the longest period of the signal being analyzed, suggesting that insufficient sampling of frequency components may be the issue when segments are shorter than 500 ms.

Areas of Agreement / Disagreement

Participants express differing views on the effectiveness of FFT for short signals, with some suggesting it is inadequate while others emphasize the importance of segment length relative to the signal's bandwidth. The discussion remains unresolved regarding the best approach for calculating power spectra of short signals.

Contextual Notes

There are limitations related to the assumptions about signal characteristics and the dependence on the definitions of segment length and frequency components, which remain unresolved.

tct212
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I am looking for a way to calculate the power spectrum of short signals of variable duration (between 200 and 500 ms). Standard methods seem wildly inaccurate. Are there any tricks for short segments?

Thanks anyone for a response.
 
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If you have access to Matlab, you should be able to take the FFt of the signal, square it and get your power spectrum. Do a google search for Power Spectrum and Matlab and you'll get a load of hits.
 
For short signals?

Thank you Dr Transport. Yes I do have access to Matlab and FFT works great for segments longer than 500 ms. When the segments are short, fft does a very bad job. I am looking for some improved algorithm that may be better optimized for short segments. Any insights would be appreciated.
 
The length of the segment in ms does not matter. What matters is the length of the segment relative to the longest period of the signal of interest (i.e. the bandwidth of the signal).
You need at sample at least one entirely cycle of each frequency component you are trying to extract in order to get sensible results; my guess would be that you are hitting that "limit" when you go below 500 ms.
 

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