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