combine spectrogram result in one figure

I have 20 min signal and would like to combine its sepectogram become one spectrogram consecutively. my idea is put index of each S, P, T value and then joining together in one array then using imagesc. But I don't know if this flow is effective, since I have to combine for each 20 minutes into a month.

I write part of coding but I don't know how to looping index for spectogram result.

Please help me.

%% SPECTROGRAM

clc, close all, clear all

set(0,'DefaultFigureWindowStyle','docked')

datafold =  uigetdir(pwd,'Select data Folder');
myfiles=dir([datafold '/*.DAT']);
N = length(myfiles) ;    % total number of files 
data = cell(N,1) 
for i = 1:N
    thisfile = myfiles(i).name ;
    y = importdata(thisfile);
    t=(0:length(y)-1)';
    Nspec=512;
    wspec=hamming(Nspec);
    Noverlap=Nspec/2;
    fs=100;
    [Si,Fi,Ti,P]=spectrogram(y,wspec,Noverlap,Nspec,fs,'xaxis');
%     nexttile
%     imagesc(T/60,F,10*log10(P));  
%     axis xy;
%     axesHandle.YLim = [0.1 10000];
%     colormap default;
%     cbar = colorbar;
%     cbar.Label.String = {'Intensity in dB'};
%     xlabel('Time (s)');
%     ylabel('Freqwency(Hz)');
%     title('Spectrogram with RemInsRes');
end

Answer 1

[Suraj Kumar]

Hi Nirwana,

Based on my understanding, you want to combine the spectrogram results of multiple signal files into a single, continuous spectrogram plot by comprehensively looping through the spectrogram for individual files.

You can refer to the following steps along with the attached code snippets :

1. Initialize two empty arrays “combined_S” and “combined_T”, to store the concatenated spectrogram data and time indices from all files.

% Initialize empty arrays for concatenated results
combined_S = [];
combined_T = [];

2. Loop through the files and calculate the spectrogram of the current file. Then concatenate the power spectral density to “combined_S” and time indices to “combined_T”.

% Calculate the spectrogram
[Si, Fi, Ti, Pi] = spectrogram(y, wspec, Noverlap, Nspec, fs, 'xaxis');
% Concatenate the results
combined_S = [combined_S, Pi];
if isempty(combined_T)
   combined_T = Ti;
else
   combined_T = [combined_T, Ti + combined_T(end)];
end

3. Then plot the combined spectrogram using “imagesc” function and further update the plot in each iteration of the loop to visualise the spectrogram built up gradually.

% Update the plot
imagesc(combined_T / 60, Fi, 10 * log10(combined_S));
axis xy;
drawnow; 

See the output below for better understanding :

For more details on the “spectrogram” and “imagesc” function, kindly refer to the following documentations:

• https://www.mathworks.com/help/signal/ref/spectrogram.html
• https://www.mathworks.com/help/matlab/ref/imagesc.html

Happy Coding!