# plotting power spectrum density

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Kashish on 21 May 2024 at 8:00
Commented: Kashish on 21 May 2024 at 9:15
I have 2 .dat file with me one of amplitude and one of time and I want to do the powerspectrum analysis of the data. Can anyone please help me in creating a time vector for doing FFT

Hassaan on 21 May 2024 at 8:32
% Load the data from the .dat files
% Check if time data is provided, otherwise create time vector
if isempty(time)
Fs = 1000; % Sampling frequency in Hz
Ts = 1 / Fs; % Sampling interval in seconds
time = (0:length(amplitude)-1) * Ts; % Time vector
end
% Compute FFT
L = length(amplitude); % Length of the signal
Y = fft(amplitude); % Compute the FFT
P2 = abs(Y / L); % Two-sided spectrum
P1 = P2(1:L/2+1); % Single-sided spectrum
P1(2:end-1) = 2 * P1(2:end-1);
f = Fs * (0:(L/2)) / L; % Frequency vector
% Calculate Power Spectrum Density (PSD)
PSD = (1 / (Fs * L)) * (abs(Y(1:L/2+1)).^2);
PSD(2:end-1) = 2 * PSD(2:end-1);
% Plot the PSD
figure;
plot(f, 10 * log10(PSD));
title('Power Spectrum Density');
xlabel('Frequency (Hz)');
ylabel('Power/Frequency (dB/Hz)');
grid on;
Notes
1. Sampling Frequency (Fs): Ensure that you know the correct sampling frequency of your data. If it is not 1000 Hz, replace Fs = 1000 with the correct value.
2. Units: The PSD is plotted in decibels (dB/Hz). The conversion is done using 10 * log10(PSD).
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Hassaan on 21 May 2024 at 8:59
fileinfo = dir('amp-A-016.dat');
num_samples = fileinfo.bytes / 2;
fid = fopen('amp-A-016.dat', 'r');
fclose(fid);
amplitude = amplitude * 0.0000374;
fileinfo = dir('time.dat');
num_samples = fileinfo.bytes / 4; % int32 = 4 bytes
fid = fopen('time.dat', 'r');
fclose(fid);
time = time / 20000; % Adjust according to your sample rate
% Compute the sampling frequency (Fs) from time data
Fs = 1 / mean(diff(time)); % Sampling frequency in Hz
% Compute FFT
L = length(amplitude); % Length of the signal
Y = fft(amplitude); % Compute the FFT
P2 = abs(Y / L); % Two-sided spectrum
P1 = P2(1:L/2+1); % Single-sided spectrum
P1(2:end-1) = 2 * P1(2:end-1);
f = Fs * (0:(L/2)) / L; % Frequency vector
% Calculate Power Spectrum Density (PSD)
PSD = (1 / (Fs * L)) * (abs(Y(1:L/2+1)).^2);
PSD(2:end-1) = 2 * PSD(2:end-1);
% Plot the PSD
figure;
plot(f, 10 * log10(PSD));
title('Power Spectrum Density');
xlabel('Frequency (Hz)');
ylabel('Power/Frequency (dB/Hz)');
grid on;
Kashish on 21 May 2024 at 9:15
thank you the code is working what if I want to do multitaper powerspectrum density method