Alan Tan

The following reply is given to Agnes over email.

Hi Agnes, The 2 initial plots are the time-frequency plots of the HHT corresponding to the 2 IMFs with of the highest energy. Subsequent plots are the IMFs, plotted against time.

Hi Asim, Ts is a single number (not a column of numbers) denoting the sampling time. If you have samples collected every, say 1 day, then set Ts = 1. Please send me an email if you have other doubts -- do not post your questions here since I do not monitor this site regularly. Thank you.

Please describe me what the plots are exactelly. I suppose that the first is the HHT of the datas, but what is the second?what is the difference between them? And the other plots are the various envelopes?
And if I have a 0.7 KHz sampling rate, than I have to give 700 as the Ts or 1/700?
Thanks for your help!

Would you guys please help me to figure out how does the Hilbert transform work??
function plot_hht(x,Ts)
% Plot the HHT.
% plot_hht(x,Ts)
% :: Syntax
% The array x is the input signal and Ts is the sampling period.
% Example on use: [x,Fs] = wavread('Hum.wav');
% plot_hht(x(1:6000),1/Fs);
% Func : emd

% Get HHT.
imf = emd(x); %emd is a function, it returns the IMF (intrinsic mode functions)

%%%%%%% The following one is to calculate Hilbert transform for each IMFs, but I do no know how it works???????@#$%%

for k = 1:length(imf)
   b(k) = sum(imf{k}.*imf{k});
   th = angle(hilbert(imf{k}));
   d{k} = diff(th)/Ts/(2*pi);
end
[u,v] = sort(-b);
b = 1-b/max(b);

% Set time-frequency plots. I do not how it plot the time-frequency figures too
N = length(x);
c = linspace(0,(N-2)*Ts,N-1);
for k = v(1:2)
   figure, plot(c,d{k},'k.','Color',b([k k k]),'MarkerSize',3);
   set(gca,'FontSize',8,'XLim',[0 c(end)],'YLim',[0 1/2/Ts]); xlabel('Time'), ylabel('Frequency');
end

Thanks for your help.