Computing confidence level in spectrum (after fft).

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Jonah Geils
Jonah Geils 2018-9-10
评论： Jonah Geils 2021-6-4
Hello,
I would like to compute confidence levels after I did a fft. What are the approaches? I tried:
1) to compute the background of the spectrum with a quadratic fit (in log-Power-spec). Afterwards I want to add the confidence interval (calculated with the variance). - Here the fit looks quite bad.
2) to use pwelch. With [pxx,f_C,pxxc] = pwelch(x,[],[],fs,'ConfidenceLevel',0.95) I get some errors:
Error using zeros
Size inputs must be integers.
Error in welch (line 81)
Sxx = zeros(nFreqs,size(x,2),class(x)); %#ok<*ZEROLIKE>
Error in pwelch (line 158)
[varargout{1:nargout}] = welch(x,esttype,varargin{:});
Error in preproc_ngk (line 701)
[pxx,f_C,pxxc] = pwelch(x,hamming(L),noverlap,fs,'ConfidenceLevel',0.95);
Maybe you know a different way to solve the problem? Or maybe there is a mistake with pwelch.
Thanks, Jonah

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