Difference between fft and pspectrum

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Takashi Fukushima 2020-9-22

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https://ww2.mathworks.cn/matlabcentral/answers/597799-difference-between-fft-and-pspectrum

评论： Takashi Fukushima 2020-9-22

I would like to do frequency analysis of EMG and found 2 different functions: fft and pspectrum. Could anyone tell me the difference between the 2 functions?

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Answer 1

Shantanu Dwivedi 2020-9-22

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https://ww2.mathworks.cn/matlabcentral/answers/597799-difference-between-fft-and-pspectrum#answer_498433

编辑：Shantanu Dwivedi 2020-9-22

The 'fft(x)' function computes the discrete Fourier transform (DFT) of x using a fast Fourier transform (FFT) algorithm.

Please refer the following link for more information about the fft function.

https://in.mathworks.com/help/matlab/ref/fft.html

The 'pspectrum(x)' function returns the power spectrum of x.

Please refer the following link for more information about the 'pspectrum' function.

https://in.mathworks.com/help/signal/ref/pspectrum.html?s_tid=srchtitle

A fast Fourier transform is an algorithm that computes the discrete Fourier transform of a sequence. Fourier Transform changes the domain of the signal from time or space to frequency domain. The DFT is obtained by decomposing a sequence of values into components of different frequencies.

The statistical average of a certain signal or sort of signal (including noise) as analyzed in terms of its frequency content, is called its spectrum. So, the power spectrum refers to the spectral energy distribution that would be found per unit time, since the total energy of such a signal over all time would generally be infinite.

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Takashi Fukushima 2020-9-22

Thank you very much for your answer.

I visited fft function page and saw this ...

Y = fft(X);

Fs = Sample frequency

L = Length of signal

P2 = abs(Y/L);

P1 = P2(1:L/2+1);

P1(2:end-1) = 2*P1(2:end-1);

f = Fs*(0:(L/2))/L;

plot(f,P1);

Could you tell me why I have to compute two-sided spectrum and convert it to single-sided spectrum? I mean I do not know where the formula comes from...

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