I have done the FFT analysis of a real time data. Please check weather am i right or not ?

clc;

clear;

close all;

%%Time Domain Plot

vib1=readtimetable("sing2.txt","SampleRate",1);

tiledlayout(5,1)

nexttile

plot(vib1.Time,vib1.Sing1)

N=length(vib1.Sing1);

xlabel("Time(s)")

ylabel("Ampl(mm/s^2)")

%% FFt

fs=1;%Sampling Frequency

delt=seconds(1/fs); %time step

t=0:1:length(vib1.Sing1)-1;

Totaltime=(length(vib1.Sing1)-1);

my_fft=2/N*(fft(vib1.Sing1));%FFT of Signal

abs_fft=abs(my_fft); %Absolute value of fft

delf=1/Totaltime; %Frequency Resolution

n2=1:1:N/2; %fft results are plotted for N/2 data points

fk=delf*n2;% frequency values

nexttile

plot(fk,abs_fft(1:N/2))

[v,p]=findpeaks(abs_fft(1:N/2),fk,'Threshold',0.03);

findpeaks(abs_fft(1:N/2),fk,'MinPeakHeight',0.03)

xlabel("Frequency (Hz)")

ylabel("Ampl(mm/s^2)")

%%Spectral density

nexttile

pspectrum(vib1.Sing1,vib1.Time,"spectrogram")

Answer 1

[Abderrahim. B]

Hi!

Looks correct to me your spectral analysis!

Screenshot from Signal Analyzer App. This app allows MATLAB script generation.

HTH!

[GOURANG UPADHYAY]

please check fft part of the code is it correct or not.

[Abderrahim. B]

The workflow is correct.

Here is an improved version of your code:

clear;
close all;

%% Read data from sing2.txt file
Fs = 1 ; % Sampling rate 
vib1 = readtimetable("sing2.txt","SampleRate", Fs);
%% Plots - Time Domain
tiledlayout(5,1)
nexttile
plot(vib1, "Sing1") 
xlabel("Time(s)")
ylabel("Ampl(mm/s^2)")

%% Compute FFT
L =length(vib1.Sing1); % Signal length
N = 2^nextpow2(L);     %  FFT length (to improve performance)

my_fft = fft(vib1.Sing1, N) ;% FFT of the Signal
abs_fft = abs(my_fft/N).^2 ; % FFT magnitude
f = Fs*(0:(N/2))/N ; % Frequency vector

%% Plot FFT magnitude
nexttile
plot(f, abs_fft(1: N/2+1))
xlabel("Frequency (Hz)")
ylabel("FFT Magnitude")

%% Find peaks in FFT magnitude
findpeaks(abs_fft(1: N/2+1) ,"MinPeakProminence",0.05*10^-3, "Annotate","extents")

%% Spectrogram
nexttile
pspectrum(vib1.Sing1,vib1.Time,"spectrogram")

[GOURANG UPADHYAY]

please check the first plot command.

and please explain the line number 16.i am new to it.and find peak command. like meannin of "Annotate" and Extents

[Abderrahim. B]

Check these MWs documentation pages:

• fft : https://www.mathworks.com/help/matlab/ref/fft.html#buvwuf3-1
• findpeaks : https://www.mathworks.com/help/signal/ref/findpeaks.html
• pspectrum: https://www.mathworks.com/help/signal/ref/pspectrum.html

GL

[GOURANG UPADHYAY]

why have you squared fft in line 16?

[Abderrahim. B]

To compute the power spectrum. You can just keep like it was in your code if you re only interested in the fft magnitude .

[GOURANG UPADHYAY]

ok thanks bro.means if i want to finad variation of frequency and amplitude then my code is correct.is it right?

[Abderrahim. B]

You re welcome. The workflow is correct.

As you can see the plots you got are the same as the plots after you run the version code that I shared and the same as the plots obtained using Signal Analyzer App.

GL

[GOURANG UPADHYAY]

ok bro

[Abderrahim. B]

If this answer helped you accept it.