# Power Spectra estimation after FFT

5 views (last 30 days)

Show older comments

Hello guys!

I am working on a frequency analysis for skin conductance. The frequencies expected on those kinds of signals are very low (between 0.045 and 0.25 Hz), so I would like to get the PSD in specific low-frequency ranges, i.e. (0 - 0.045), (0.045 - 0.15), (0.15 - 0.25), and the total power of the signal. To do so, I computed the Fast Fourier Transform, but now the problem is computing the power spectrum after the fourier.

The tutorials from Matlab have not been of much help, and also there are so many functions that can be used that I'm feeling a little lost at the moment! Can anyone help me work out this issue? Among the many options, which one do you think works best, in terms of both efficacy and computational time? I'm not looking for anything too fancy really, just an efficacious and standard protocol.

The processing pipeline I am following is:

- 8th order Chebyshev Type I lowpass filter, with 0.8 cutoff
- Downsampling from 4 to 2 Hz (factor = 2)
- 8th order Butterworth highpass filter with 0.01 cutoff (do you think is appropriate, given that I'm mostly interested in low frequencies?)
- Welch's periodogram (50% overlap)
- Blackman window (128 points) applied to each segment
- FFT computer on each windowed segment

I also attached the code because it would be amazing to have examples or suggestions about how to proceed based on real examples! Any advice is always appreciated!

Thank you very much to any of you who is willing to help!

Luca

### Accepted Answer

LO
on 13 Jul 2020

try this example:

sampling_freq = 5000

window = 8192,

noverlap = 4096,

nfft = 8192,

[p,f] = pwelch(your_signal, 8192,4096,8192,5000);

max_power=10*log10(max(p)); % this would be the max power

plot(f,10*log10(p)); % this would be the power plot

##### 4 Comments

LO
on 14 Jul 2020

Edited: LO
on 14 Jul 2020

### More Answers (0)

### See Also

### Categories

### Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!