How to visualize time frequency information of time series signal using continuous wavelet transform

I have time series signal named X with variable Sg. I want to visualize it’s time frequency information by using continuous wavelet transform with the following input parameters:

samplingperiod=0.25;

scale = 24;

Fs = 4;

t = 0:1/Fs:(numel(Sg)-1)/Fs;

t = 0:1/Fs:(numel(Sg)-1)/Fs;

wavelet name = ‘db2’

I have tried the following script and got the following output (time scale information)

clear

load('X.mat')

samplingperiod=0.25;

scale = 24;

Fs = 4;

t = 0:1/Fs:(numel(Sg)-1)/Fs;

ax = newplot;

c = cwt(Sg,scale,'db2','plot');

colormap('jet(227)')

axis tight;

cb = colorbar(ax);

However what I need is a time- frequency information with a frequency range of 0 up to 2 Hz and time in second (4800/4 =1200 second) like the following figure

Thank you for contribution in advance

Answer 1

[Mathieu NOE]

hello

I used this FEX submission as I don't have the Wavelet Toolbox

cmccrimm/Continuous-Wavelet-Transform - File Exchange - MATLAB Central (mathworks.com)

Your code adapted is as follows. Note you can "zoom" the dB scale to better see the small signals rendering - here I choosed 40 dB of max scale.

clear
load('X.mat')
Fs = 4;
t = (0:numel(Sg)-1)/Fs;
ax = newplot;
[y,f,coi] = cwt(Sg,Fs);

% reduction of the dB scale : only display max to min = max - Range_dB
Range_dB = 40; %  dB scale
out_dB = 20*log10(abs(y));
ind = find(out_dB< max(out_dB,[],'all')-Range_dB);
out_dB(ind) = NaN;

imagesc(t,f,out_dB);
xlabel('Time (s)')
ylabel('Frequency (Hz)')
colormap('jet(128)')
axis tight;
cb = colorbar(ax);
set(gca,'YDir','normal');

[Yared Daniel]

Thank you Mr Mathieu for responding but what is the wavelet family? can this applicable for db or sym family? and the does the decible scale related with scale of the wavelet?

[Mathieu NOE]

hello Yared

sorry, I am not expert in wavelet , I am until now using more basic fft tools . I have to learn a bit more myself on wavelet ...