Converting discrete signal to frequency domain

Hi i am new to Matlab. My question is if i have a discrete signal (experiment data) stored in a variable like

onetrial = 1x200;

sampled a frequency of 100hz. How can i convert it into frequency domain and plot it.

Also how can i go about plotting its PSD(power spectral density)?

Thanks in advance.

Answer 1

[Star Strider]

The fft calculation an plotting is straightforward. (You can also use the pspectrum function and others.)

Fs = 100;
Fn = Fs/2;
Ts = 1/Fs;
t = linspace(0, 199, 200)/Fs;                               % Time Vector
onetrial = sin(2*pi*10*t) + randn(1,200)*0.1;               % Signal Vector
L = numel(t);
NFFT = 2^nextpow2(L);                                       % Fourier Transform Length Power-Of-Two For Efficiency
FT_onetrial = fft(onetrial - mean(onetrial), NFFT)/L;       % Fourier Transform
Fv = linspace(0, 1, NFFT/2+1)*Fn;                           % Frequency Vector
Iv = 1:numel(Fv);                                           % Index Vector

figure
plot(Fv, abs(FT_onetrial(Iv))-2)
grid
xlabel('Frequency (Hz)')
ylabel('Amplitude')

To calculate the PSD there are several options, one of which is the pwelch function.

.